Tektronix 2182A Primary User

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Model 2182A Nanovoltmeter

User’s Manual

2182A-900-01 Rev. C July 2022

tek.com/keithley

*P2182A-900-01C*

2182A-900-01C

Nanovoltmeter

User's Manual

Model 2182A

Cleveland, Ohio, U.S.A.

Any unauthorized reproduction, photocopy, or use of the information herein, in whole or in part,

without the prior written approval of Keithley Instruments, LLC, is strictly prohibited.

These are the original instructions in English.

All Keithley Instruments product names are trademarks or registered trademarks of Keithley

Instruments, LLC. Other brand names are trademarks or registered trademarks of their respective

holders.

Microsoft, Visual C++, Excel, and Windows are either registered trademarks or trademarks of

Microsoft Corporation in the United States and/or other countries.

Document number: 2182A-900-01 Rev. C July 2022

Safety precautions

The following safety precautions should be observed before using this product and any associated instrumentation. Although some instruments and accessories would normally be used with nonhazardous voltages, there are situations where hazardous conditions may be present.

This product is intended for use by personnel who recognize shock hazards and are familiar with the safety precautions required to avoid possible injury. Read and follow all installation, operation, and maintenance information carefully before using the product. Refer to the user documentation for complete product specifications.

If the product is used in a manner not specified, the protection provided by the product warranty may be impaired. The types of product users are: Responsible body is the individual or group responsible for the use and maintenance of equipment, for ensuring that the

equipment is operated within its specifications and operating limits, and for ensuring that operators are adequately trained. Operators use the product for its intended function. They must be trained in electrical safety procedures and proper use of the

instrument. They must be protected from electric shock and contact with hazardous live circuits. Maintenance personnel perform routine procedures on the product to keep it operating properly, for example, setting the line

voltage or replacing consumable materials. Maintenance procedures are described in the user documentation. The procedures explicitly state if the operator may perform them. Otherwise, they should be performed only by service personnel.

Service personnel are trained to work on live circuits, perform safe installations, and repair products. Only properly trained service personnel may perform installation and service procedures.

Keithley products are designed for use with electrical signals that are measurement, control, and data I/O connections, with low transient overvoltages, and must not be directly connected to mains voltage or to voltage sources with high transient overvoltages. Measurement Category II (as referenced in IEC 60664) connections require protection for high transient overvoltages often associated with local AC mains connections. Certain Keithley measuring instruments may be connected to mains. These instruments will be marked as category II or higher.

Unless explicitly allowed in the specifications, operating manual, and instrument labels, do not connect any instrument to mains. Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable connector jacks or test

fixtures. The American National Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than 30 V RMS, 42.4 V peak, or 60 VDC are present. A good safety practice is to expect that hazardous voltage is present in any unknown circuit before measuring.

Operators of this product must be protected from electric shock at all times. The responsible body must ensure that operators are prevented access and/or insulated from every connection point. In some cases, connections must be exposed to potential human contact. Product operators in these circumstances must be trained to protect themselves from the risk of electric shock. If the circuit is capable of operating at or above 1000 V, no conductive part of the circuit may be exposed.

Do not connect switching cards directly to unlimited power circuits. They are intended to be used with impedance-limited sources. NEVER connect switching cards directly to AC mains. When connecting sources to switching cards, install protective devices to limit fault current and voltage to the card.

Before operating an instrument, ensure that the line cord is connected to a properly-grounded power receptacle. Inspect the connecting cables, test leads, and jumpers for possible wear, cracks, or breaks before each use.

When installing equipment where access to the main power cord is restricted, such as rack mounting, a separate main input power disconnect device must be provided in close proximity to the equipment and within easy reach of the operator.

For maximum safety, do not touch the product, test cables, or any other instruments while power is applied to the circuit under test. ALWAYS remove power from the entire test system and discharge any capacitors before connecting or disconnecting cables or jumpers, installing or removing switching cards, or making internal changes, such as installing or removing jumpers.

Do not touch any object that could provide a current path to the common side of the circuit under test or power line (earth) ground. Always make measurements with dry hands while standing on a dry, insulated surface capable of withstanding the voltage being measured.

For safety, instruments and accessories must be used in accordance with the operating instructions. If the instruments or accessories are used in a manner not specified in the operating instructions, the protection provided by the equipment may be impaired.

Do not exceed the maximum signal levels of the instruments and accessories. Maximum signal levels are defined in the specifications and operating information and shown on the instrument panels, test fixture panels, and switching cards.

When fuses are used in a product, replace with the same type and rating for continued protection against fire hazard. Chassis connections must only be used as shield connections for measuring circuits, NOT as protective earth (safety ground)

connections. If you are using a test fixture, keep the lid closed while power is applied to the device under test. Safe operation requires the use

of a lid interlock.

If a screw is present, connect it to protective earth (safety ground) using the wire recommended in the user documentation.

The symbol on an instrument means caution, risk of hazard. The user must refer to the operating instructions located in the user documentation in all cases where the symbol is marked on the instrument.

The symbol on an instrument means warning, risk of electric shock. Use standard safety precautions to avoid personal contact with these voltages.

The symbol on an instrument shows that the surface may be hot. Avoid personal contact to prevent burns.

The symbol indicates a connection terminal to the equipment frame.

If this symbol is on a product, it indicates that mercury is present in the display lamp. Please note that the lamp must be properly disposed of according to federal, state, and local laws.

The WARNING heading in the user documentation explains hazards that might result in personal injury or death. Always read the associated information very carefully before performing the indicated procedure.

The CAUTION heading in the user documentation explains hazards that could damage the instrument. Such damage may invalidate the warranty.

The CAUTION heading with the symbol in the user documentation explains hazards that could result in moderate or minor injury or damage the instrument. Always read the associated information very carefully before performing the indicated procedure. Damage to the instrument may invalidate the warranty.

Instrumentation and accessories shall not be connected to humans. Before performing any maintenance, disconnect the line cord and all test cables. To maintain protection from electric shock and fire, replacement components in mains circuits — including the power

transformer, test leads, and input jacks — must be purchased from Keithley. Standard fuses with applicable national safety approvals may be used if the rating and type are the same. The detachable mains power cord provided with the instrument may only be replaced with a similarly rated power cord. Other components that are not safety-related may be purchased from other suppliers as long as they are equivalent to the original component (note that selected parts should be purchased only through Keithley to maintain accuracy and functionality of the product). If you are unsure about the applicability of a replacement component, call a Keithley office for information.

Unless otherwise noted in product-specific literature, Keithley instruments are designed to operate indoors only, in the following environment: Altitude at or below 2,000 m (6,562 ft); temperature 0 °C to 50 °C (32 °F to 122 °F); and pollution degree 1 or 2.

To clean an instrument, use a cloth dampened with deionized water or mild, water-based cleaner. Clean the exterior of the instrument only. Do not apply cleaner directly to the instrument or allow liquids to enter or spill on the instrument. Products that consist of a circuit board with no case or chassis (e.g., a data acquisition board for installation into a computer) should never require cleaning if handled according to instructions. If the board becomes contaminated and operation is affected, the board should be returned to the factory for proper cleaning/servicing.

Safety precaution revision as of June 2018.

Introduction ............................................................................................................... 1-1

Welcome .............................................................................................................................. 1-1

Extended warranty ............................................................................................................... 1-2

Contact information .............................................................................................................. 1-2

Organization of manual sections .......................................................................................... 1-2

General ratings ..................................................................................................................... 1-3

Installation ................................................................................................................. 2-1

Instrument power ................................................................................................................. 2-1

Changing the line voltage .......................................................................................................... 2-2

Line power connection .............................................................................................................. 2-3

Power-up sequence .................................................................................................................. 2-4

Remote communications interfaces ..................................................................................... 2-4

Programming languages ........................................................................................................... 2-4

RS-232 connections ............................................................................................................. 2-5

RS-232 interface selection and configuration ...................................................................... 2-6

Flow control (signal handshaking) ............................................................................................. 2-7

GPIB setup ........................................................................................................................... 2-8

Install the GPIB driver software ................................................................................................. 2-8

Install the GPIB cards in your computer .................................................................................... 2-8

GPIB bus connections ............................................................................................................... 2-8

GPIB interface selection and configuration ............................................................................. 2-11

Front-panel GPIB operation ............................................................................................... 2-12

GPIB status indicators ............................................................................................................. 2-12

LOCAL key .............................................................................................................................. 2-12

General bus commands ..................................................................................................... 2-13

DCL (device clear) .................................................................................................................. 2-13

GET (group execute trigger).................................................................................................... 2-13

GTL (go to local) ..................................................................................................................... 2-14

IFC (interface clear) ................................................................................................................ 2-14

LLO (local lockout) .................................................................................................................. 2-15

REN (remote enable) .............................................................................................................. 2-15

SDC (selective device clear) ................................................................................................... 2-15

SPE, SPD (serial polling) ........................................................................................................ 2-16

Transmit routines .................................................................................................................... 2-16

Instrument description ............................................................................................. 3-1

Front-panel overview ............................................................................................................ 3-1

1 Display annunciators .............................................................................................................. 3-2

2 SHIFT key, LOCAL key, and POWER switch ......................................................................... 3-3

3 Function keys ......................................................................................................................... 3-3

4 Range keys ............................................................................................................................ 3-5

5 Handle .................................................................................................................................... 3-5

6 Input connector ...................................................................................................................... 3-5

Rear-panel overview ............................................................................................................ 3-5

1 ANALOG OUTPUT ................................................................................................................ 3-5

Table of contents Model 2182A Nanovoltmeter User's Manual

2 TRIGGER LINK ...................................................................................................................... 3-6

3 RS-232 ................................................................................................................................... 3-6

4 IEEE-488 ................................ ................................................................ ................................ 3-6

5 Power module ........................................................................................................................ 3-6

Error and status messages .................................................................................................. 3-6

Default settings .................................................................................................................... 3-7

Reset the instrument ............................................................................................................ 3-9

Setting the number of displayed digits ................................................................................. 3-9

Making measurements ............................................................................................. 4-1

Measurement overview ........................................................................................................ 4-1

Using the front-panel display ..................................................................................................... 4-2

Voltage measurements ............................................................................................................. 4-2

Temperature measurements ..................................................................................................... 4-2

Warm-up .............................................................................................................................. 4-3

ACAL (calibration) ................................................................................................................ 4-3

Measuring internal temperature ................................................................................................ 4-4

Checking TCAL temperature ..................................................................................................... 4-4

Test connections .................................................................................................................. 4-5

Connection techniques .............................................................................................................. 4-5

Measurement techniques ........................................................................................................ 4-10

Temperature-only connections ................................................................................................ 4-11

Voltage and temperature connections ..................................................................................... 4-12

Cleaning test circuit connectors .............................................................................................. 4-13

Measuring voltage and temperature .................................................................................. 4-14

Temperature configuration ...................................................................................................... 4-14

SCPI commands - voltage and temperature measurements ................................................... 4-15

Range ................................................................................................................................. 4-15

Maximum range readings ........................................................................................................ 4-16

Manual ranging ....................................................................................................................... 4-16

Autoranging ............................................................................................................................. 4-17

SCPI programming - range ..................................................................................................... 4-17

Autozero modes ................................................................................................................. 4-17

Front Autozero ........................................................................................................................ 4-17

Autozero .................................................................................................................................. 4-18

Rate .................................................................................................................................... 4-19

SCPI programming - rate ........................................................................................................ 4-20

Filters.................................................................................................................................. 4-20

Analog filter ............................................................................................................................. 4-21

Digital filter .............................................................................................................................. 4-21

SCPI programming - filter ........................................................................................................ 4-25

Relative offset .................................................................................................................... 4-25

SCPI programming - relative offset ......................................................................................... 4-26

Pumpout current (low charge injection mode) ................................................................... 4-27

Line cycle synchronization ................................................................................................. 4-27

SCPI programming - Line cycle synchronization ..................................................................... 4-28

Calculations that you can apply to measurements ............................................................ 4-28

Model 2182A Nanovoltmeter User's Manual Table of contents

mx+b ....................................................................................................................................... 4-29

Percent (%) ............................................................................................................................. 4-30

SCPI programming - mx+b and percent .................................................................................. 4-30

Ratio ................................................................................................................................... 4-31

SCPI command - ratio ............................................................................................................. 4-32

Range settings when using ratio ............................................................................................. 4-32

Relative offset when using ratio .............................................................................................. 4-33

Analog output ..................................................................................................................... 4-34

Temperature ............................................................................................................................ 4-35

Ratio ........................................................................................................................................ 4-35

Analog output connections ...................................................................................................... 4-35

Configure the analog output .................................................................................................... 4-36

Analog output relative offset .................................................................................................... 4-36

SCPI programming - analog output ......................................................................................... 4-36

Applications ........................................................................................................................ 4-37

Heated Zener reference and Josephson Junction Array comparisons .................................... 4-37

Calibrating resistor network dividers ....................................................................................... 4-37

Testing superconductor materials ........................................................................................... 4-39

Low-resistance measurements ............................................................................................... 4-45

Measurement considerations .................................................................................. 5-1

Introduction .......................................................................................................................... 5-1

Thermoelectric potentials ..................................................................................................... 5-2

Thermoelectric coefficients........................................................................................................ 5-2

Thermoelectric generation ................................................................................................... 5-3

Minimizing thermal EMFs .......................................................................................................... 5-4

Canceling residual thermal offsets ............................................................................................ 5-4

AC pick-up noise .................................................................................................................. 5-5

Source resistance noise ....................................................................................................... 5-5

Johnson noise equation ............................................................................................................ 5-5

Minimizing source resistance noise ........................................................................................... 5-6

Magnetic fields ..................................................................................................................... 5-6

Radio frequency interference ............................................................................................... 5-7

Ground loops ........................................................................................................................ 5-7

Shielding .............................................................................................................................. 5-9

Meter loading ..................................................................................................................... 5-10

Delta, pulse delta, and differential conductance .................................................... 6-1

Overview .............................................................................................................................. 6-1

Enabling the Delta measurement mode .................................................................................... 6-4

Filter considerations for delta measurements............................................................................ 6-5

Delta measurement procedure using a SourceMeter ................................................................ 6-5

Delta measurement procedure using a Model 622x .......................................................... 6-10

Keithley instrumentation requirements .................................................................................... 6-10

Operation overview ................................................................................................................. 6-11

Test system configurations...................................................................................................... 6-14

Delta measurement process ................................................................................................... 6-15

Pulse delta measurements ...................................................................................................... 6-17

Table of contents Model 2182A Nanovoltmeter User's Manual

Pulse delta outputs .................................................................................................................. 6-19

Differential conductance measurement process ..................................................................... 6-22

Stepping and scanning ............................................................................................ 7-1

Step and scan overview ....................................................................................................... 7-1

SCPI programming - stepping and scanning ....................................................................... 7-1

Internal stepping and scanning ............................................................................................ 7-2

Other stepping and scanning operations ................................................................................... 7-3

Stepping and scanning controls ................................................................................................ 7-4

Internal stepping and scanning settings .................................................................................... 7-4

Internal scanning example ........................................................................................................ 7-5

Internal stepping example ......................................................................................................... 7-6

External stepping and scanning (channel 1) ........................................................................ 7-7

External stepping and scanning settings ................................................................................... 7-7

Constant magnetic field or temperature example ................................................................ 7-8

Set up the 2182A ...................................................................................................................... 7-9

Set up the 2400 ....................................................................................................................... 7-10

Run the scan from the front panel ........................................................................................... 7-10

Run the scan using code ......................................................................................................... 7-11

Code to calculate the dc current reversal data ........................................................................ 7-12

Reading buffers ........................................................................................................ 8-1

Buffer operations .................................................................................................................. 8-1

Store ..................................................................................................................................... 8-1

Recall ................................................................................................................................... 8-2

Buffer statistics ..................................................................................................................... 8-3

SCPI programming - buffer .................................................................................................. 8-4

Triggering .................................................................................................................. 9-1

Trigger model ....................................................................................................................... 9-1

Front-panel trigger model ..................................................................................................... 9-2

Idle ............................................................................................................................................ 9-2

Trigger model (remote operation) ........................................................................................ 9-2

Idle and initiate .......................................................................................................................... 9-4

Control source and event detection ..................................................................................... 9-5

Delay .................................................................................................................................... 9-5

Device action ........................................................................................................................ 9-6

Output trigger ....................................................................................................................... 9-7

Reading hold (autosettle) ..................................................................................................... 9-7

Enable or disable the reading hold beeper ................................................................................ 9-8

External triggering ................................................................................................................ 9-8

External trigger .......................................................................................................................... 9-9

Voltmeter complete ................................................................................................................... 9-9

External triggering example..................................................................................................... 9-10

Model 2182A Nanovoltmeter User's Manual Table of contents

External triggering with BNC connections ............................................................................... 9-14

Trigger model operation ..................................................................................................... 9-15

Triggering commands ........................................................................................................ 9-16

Programming example ....................................................................................................... 9-16

Limits ....................................................................................................................... 10-1

Limit operations .................................................................................................................. 10-1

Setting limit values ............................................................................................................. 10-2

Enabling limits .................................................................................................................... 10-2

SCPI programming - limits ................................................................................................. 10-3

Application for sorting resistors .......................................................................................... 10-3

Maintenance ................................ ............................................................................ 11-1

Introduction ........................................................................................................................ 11-1

Cleaning input connectors ................................................................................................. 11-1

Line fuse replacement ........................................................................................................ 11-2

Upgrading the firmware ...................................................................................................... 11-4

Status and error messages ................................................................................................ 11-4

Error messages ....................................................................................................................... 11-4

Status messages ..................................................................................................................... 11-6

Calibration messages .............................................................................................................. 11-6

DDC Status Model messages ................................................................................................. 11-7

Keithley 182 Serial Poll Byte Events ....................................................................................... 11-8

Introduction to SCPI commands ............................................................................ 12-1

Programming syntax .......................................................................................................... 12-1

Command words ..................................................................................................................... 12-1

Query commands .................................................................................................................... 12-3

Program messages ................................................................................................................. 12-3

Response messages ............................................................................................................... 12-5

Multiple response messages ................................................................................................... 12-5

Message exchange protocol ................................................................................................... 12-6

Using the SCPI command reference ................................................................................. 12-6

Command name and summary table ...................................................................................... 12-7

Command usage ..................................................................................................................... 12-8

Command details .................................................................................................................... 12-8

Example section ...................................................................................................................... 12-9

Related commands list ............................................................................................................ 12-9

QuickBASIC programming ............................................................................................... 12-10

About program fragments...................................................................................................... 12-10

SCPI command reference ....................................................................................... 13-1

:CONFigure:<function> ........................................................................................................... 13-1

:FETCh? .................................................................................................................................. 13-3

Table of contents Model 2182A Nanovoltmeter User's Manual

:MEASure? .............................................................................................................................. 13-4

:READ? ................................................................................................................................... 13-5

CALCulate[1] subsystem.................................................................................................... 13-6

:CALCulate[1]:DATA? ............................................................................................................. 13-7

:CALCulate[1]:FORMat ........................................................................................................... 13-7

:CALCulate[1]:KMATh:MBFactor ............................................................................................ 13-8

:CALCulate[1]:KMATh:MMFactor ............................................................................................ 13-9

:CALCulate[1]:KMATh:MUNits .............................................................................................. 13-10

:CALCulate[1]:KMATh:PERCent ........................................................................................... 13-11

:CALCulate[1]:KMATh:PERCent:ACQuire ............................................................................ 13-12

:CALCulate[1]:STATe ............................................................................................................ 13-12

CALCulate2 subsystem.................................................................................................... 13-13

:CALCulate2:DATA? ............................................................................................................. 13-13

:CALCulate2:FORMat ........................................................................................................... 13-13

:CALCulate2:IMMediate ........................................................................................................ 13-14

:CALCulate2:STATe .............................................................................................................. 13-15

CALCulate3 subsystem.................................................................................................... 13-16

:CALCulate3:IMMediate ........................................................................................................ 13-16

:CALCulate3:LIMit2:CLEar:AUTO ......................................................................................... 13-17

:CALCulate3:LIMit2:CLEar[:IMMediate] ................................................................................ 13-17

:CALCulate3:LIMit2:FAIL?..................................................................................................... 13-18

:CALCulate3:LIMit2:LOWer[:DATA] ...................................................................................... 13-18

:CALCulate3:LIMit2:STATe ................................................................................................... 13-19

:CALCulate3:LIMit2:UPPer[:DATA] ....................................................................................... 13-20

:CALCulate3:LIMit[1]:CLEar:AUTO ....................................................................................... 13-21

:CALCulate3:LIMit[1]:CLEar[:IMMediate] .............................................................................. 13-21

:CALCulate3:LIMit[1]:FAIL?................................................................................................... 13-22

:CALCulate3:LIMit[1]:LOWer[:DATA] .................................................................................... 13-22

:CALCulate3:LIMit[1]:STATe ................................................................................................. 13-24

:CALCulate3:LIMit[1]:UPPer[:DATA] ..................................................................................... 13-25

CALibration subsystem .................................................................................................... 13-26

:CALibration:UNPRotected:ACALibration:INITiate ................................................................ 13-26

:CALibration:UNPRotected:ACALibration:STEP1 ................................................................. 13-27

:CALibration:UNPRotected:ACALibration:STEP2 ................................................................. 13-27

:CALibration:UNPRotected:ACALibration:DONE .................................................................. 13-28

:CALibration:UNPRotected:ACALibration:TEMPerature? ..................................................... 13-28

DISPlay subsystem .......................................................................................................... 13-29

:DISPlay:ENABle ................................................................................................................... 13-29

:DISPlay[:WINDow[1]]:TEXT:DATA ...................................................................................... 13-29

:DISPlay[:WINDow[1]]:TEXT:STATe ..................................................................................... 13-30

FORMat subsystem ......................................................................................................... 13-30

:FORMat:BORDer ................................................................................................................. 13-31

:FORMat[:DATA] ................................................................................................................... 13-32

:FORMat:ELEMents .............................................................................................................. 13-35

OUTPut subsystem .......................................................................................................... 13-36

:OUTPut:GAIN ...................................................................................................................... 13-36

:OUTPut:OFFSet ................................................................................................................... 13-37

:OUTPut:RELative ................................................................................................................. 13-37

:OUTPut[:STATe] .................................................................................................................. 13-38

ROUTe subsystem ........................................................................................................... 13-39

:ROUTe:SCAN:INTernal:CCOunt ......................................................................................... 13-39

:ROUTe:SCAN:LSELect ....................................................................................................... 13-40

:ROUTe:SCAN[:EXTernal] .................................................................................................... 13-41

SENSe[1] subsystem ....................................................................................................... 13-41

Model 2182A Nanovoltmeter User's Manual Table of contents

:SENSe[1]:<function>:DIGits ................................................................................................. 13-41

:SENSe[1]:<function>:APERture ........................................................................................... 13-42

:SENSe[1]:<function>:NPLCycles ......................................................................................... 13-43

:SENSe[1]:<function>[:CHANnel<X>]:DFILter:COUNt .......................................................... 13-45

:SENSe[1]:<function>[:CHANnel<X>]:DFILter:TCONtrol ...................................................... 13-46

:SENSe[1]:<function>[:CHANnel<X>]:DFILter:WINDow ....................................................... 13-47

:SENSe[1]:<function>[:CHANnel<X>]:DFILter[:STATe] ........................................................ 13-48

:SENSe[1]:<function>[:CHANnel<X>]:LPASs[:STATe] ......................................................... 13-49

:SENSe[1]:<function>[:CHANnel<X>]:REFerence ................................................................ 13-50

:SENSe[1]:<function>[:CHANnel<X>]:REFerence:ACQuire.................................................. 13-51

:SENSe[1]:<function>[:CHANnel<X>]:REFerence:STATe .................................................... 13-52

:SENSe[1]:CHANnel ............................................................................................................. 13-53

:SENSe[1]:DATA:FRESh? .................................................................................................... 13-54

:SENSe[1]:DATA[:LATest]?................................................................................................... 13-54

:SENSe[1]:FUNCtion ............................................................................................................. 13-55

:SENSe[1]:HOLD:COUNt ...................................................................................................... 13-55

:SENSe[1]:HOLD:STATe ...................................................................................................... 13-56

:SENSe[1]:HOLD:WINDow ................................................................................................... 13-56

:SENSe[1]:TEMPerature:RJUNction:RSELect ...................................................................... 13-57

:SENSe[1]:TEMPerature:RJUNction:SIMulated .................................................................... 13-58

:SENSe[1]:TEMPerature:RTEMperature? ............................................................................. 13-58

:SENSe[1]:TEMPerature:TCouple[:TYPE] ............................................................................ 13-59

:SENSe[1]:TEMPerature:TRANsducer .................................................................................. 13-60

:SENSe[1]:VOLTage[:DC]:CHANnel2:LQMode .................................................................... 13-61

:SENSe[1]:VOLTage[:DC]:DELTa ......................................................................................... 13-61

:SENSe[1]:VOLTage[:DC]:RATio .......................................................................................... 13-63

:SENSe[1]:VOLTage[:DC][:CHANnel<X>]:RANGe[:UPPer] .................................................. 13-64

:SENSe[1]:VOLTage[:DC][:CHANnel<X>]:RANGe:AUTO .................................................... 13-65

STATus subsystem .......................................................................................................... 13-66

:STATus:MEASurement:CONDition? .................................................................................... 13-66

:STATus:MEASurement:ENABle .......................................................................................... 13-66

:STATus:MEASurement[:EVENt]? ........................................................................................ 13-68

:STATus:OPERation:CONDition? ......................................................................................... 13-70

:STATus:OPERation:ENABle ................................................................................................ 13-70

:STATus:OPERation[:EVENt]? .............................................................................................. 13-71

:STATus:PRESet .................................................................................................................. 13-73

:STATus:QUEStionable:CONDition? .................................................................................... 13-73

:STATus:QUEStionable:ENABle ........................................................................................... 13-74

:STATus:QUEStionable[:EVENt]? ......................................................................................... 13-75

:STATus:QUEue:CLEar ........................................................................................................ 13-76

:STATus:QUEue:DISable ...................................................................................................... 13-77

:STATus:QUEue:ENABle ...................................................................................................... 13-78

:STATus:QUEue[:NEXT]? ..................................................................................................... 13-79

SYSTem subsystem ......................................................................................................... 13-80

:SYSTem:AZERo[:STATe] .................................................................................................... 13-80

:SYSTem:BEEPer[:STATe] ................................................................................................... 13-81

:SYSTem:CLEar .................................................................................................................... 13-81

:SYSTem:ERRor? ................................................................................................................. 13-82

:SYSTem:FAZero[:STATe] .................................................................................................... 13-83

:SYSTem:KCLick .................................................................................................................. 13-84

:SYSTem:KEY ....................................................................................................................... 13-84

:SYSTem:LFRequency? ....................................................................................................... 13-86

:SYSTem:LSYNc[:STATe]..................................................................................................... 13-86

:SYSTem:POSetup ............................................................................................................... 13-87

:SYSTem:PRESet ................................................................................................................. 13-88

:SYSTem:TSTamp:RESet ..................................................................................................... 13-88

:SYSTem:VERSion? ............................................................................................................. 13-88

TRACe subsystem ........................................................................................................... 13-89

Table of contents Model 2182A Nanovoltmeter User's Manual

:TRACe:CLEar ...................................................................................................................... 13-89

:TRACe:DATA? ..................................................................................................................... 13-90

:TRACe:FEED ....................................................................................................................... 13-91

:TRACe:FEED:CONTrol ........................................................................................................ 13-92

:TRACe:FREE? ..................................................................................................................... 13-93

:TRACe:POINts ..................................................................................................................... 13-93

TRIGger subsystem ......................................................................................................... 13-94

:ABORt .................................................................................................................................. 13-94

:INITiate:CONTinuous ........................................................................................................... 13-94

:INITiate[:IMMediate] ............................................................................................................. 13-95

:SAMPle:COUNt .................................................................................................................... 13-96

:TRIGger[:SEQuence[1]]:COUNt ........................................................................................... 13-97

:TRIGger[:SEQuence[1]]:DELay ........................................................................................... 13-97

:TRIGger[:SEQuence[1]]:DELay:AUTO ................................................................................ 13-98

:TRIGger[:SEQuence[1]]:SIGNal ........................................................................................... 13-99

:TRIGger[:SEQuence[1]]:SOURce ........................................................................................ 13-99

:TRIGger[:SEQuence[1]] :TIMer .......................................................................................... 13-101

UNIT subsystem ............................................................................................................. 13-102

:UNIT:TEMPerature ............................................................................................................ 13-102

Common commands .............................................................................................. 14-1

Introduction ........................................................................................................................ 14-1

*CLS ........................................................................................................................................ 14-1

*ESE ....................................................................................................................................... 14-2

*ESR? ..................................................................................................................................... 14-4

*IDN? ...................................................................................................................................... 14-6

*OPC ....................................................................................................................................... 14-7

*OPC? ..................................................................................................................................... 14-8

*RCL ..................................................................................................................................... 14-10

*RST ..................................................................................................................................... 14-10

*SAV ..................................................................................................................................... 14-11

*SRE ..................................................................................................................................... 14-12

*STB? .................................................................................................................................... 14-13

*TRG ..................................................................................................................................... 14-15

*TST? .................................................................................................................................... 14-16

*WAI ...................................................................................................................................... 14-16

Program examples .................................................................................................. 15-1

Introduction ........................................................................................................................ 15-1

Changing function and range ............................................................................................. 15-1

One-shot triggering ............................................................................................................ 15-2

Generating SRQ on buffer full ............................................................................................ 15-3

Storing readings in the buffer ............................................................................................. 15-4

Controlling the 2182A using the RS-232 COM2 port ......................................................... 15-6

Status model ................................................................ ........................................... 16-1

Status structure .................................................................................................................. 16-1

Status byte register overview .................................................................................................. 16-2

Queues ............................................................................................................................... 16-6

Model 2182A Nanovoltmeter User's Manual Table of contents

Condition registers ............................................................................................................. 16-7

Event registers ................................................................................................................... 16-7

Enable registers ................................................................................................................. 16-8

Status byte and service request (SRQ) ............................................................................. 16-9

Status byte register ............................................................................................................... 16-10

Service request enable register ............................................................................................. 16-11

Serial poll and SRQ ............................................................................................................... 16-11

Model 182 emulation commands ........................................................................... 17-1

Introduction ........................................................................................................................ 17-1

182 device-dependent command summary ....................................................................... 17-1

IEEE-488 bus overview ........................................................................................... 18-1

Introduction ........................................................................................................................ 18-1

Bus description ................................................................................................................... 18-2

Bus lines ............................................................................................................................. 18-3

Data lines ................................................................................................................................ 18-3

Bus management lines ............................................................................................................ 18-4

Handshake lines ...................................................................................................................... 18-4

Bus commands .................................................................................................................. 18-5

Uniline commands ................................................................................................................... 18-6

Universal multiline commands ................................................................................................. 18-6

Addressed multiline commands .............................................................................................. 18-7

Addressed commands ............................................................................................................ 18-7

Unaddressed commands ........................................................................................................ 18-7

Common commands ............................................................................................................... 18-8

SCPI commands ..................................................................................................................... 18-8

Command codes ..................................................................................................................... 18-8

Hexadecimal and decimal values for the common commands................................................ 18-9

Typical command sequences ................................................................................................ 18-10

IEEE command groups ......................................................................................................... 18-11

Interface function codes ................................................................................................... 18-11

In this section:

Welcome ...................................................................................1-1

Extended warranty ....................................................................1-2

Contact information ...................................................................1-2

Organization of manual sections ...............................................1-2

General ratings .........................................................................1-3

Welcome

The two-channel Model 2182A Nanovoltmeter is optimized for making stable, low noise voltage measurements and for characterizing low resistance materials and devices reliably and repeatably.

Features of the 2182A Nanovoltmeter include:

• 1 nV sensitivity to provide accurate ultra-low voltage measurements.

• Typically just 15 nV peak-to-peak noise at 1 s response time, with 40 nV to 50 nV peak-to-peak

noise at 60 ms, which ensures low noise levels over a wide range of useful response times.

• Dual channels support measuring voltage, temperature, or the ratio of an unknown resistance to

a reference resistor.

• Measurement cycle is synchronized to the power line ac cycle to minimize variations due to

readings that begin at different phases of the line cycle. The result is exceptionally high immunity to line interference with little or no shielding and filtering required.

• Built-in thermocouple linearization and cold junction compensation to simplify making accurate

temperature measurements.

• Internal polarity reversal measurement technique to eliminate thermal error sources.

• Optimized for use with the Keithley Model 6220 and 6221 current sources, which allows both

instruments to be operated like a single instrument when making differential conductance, pulsed, and resistance measurements.

• Delta mode current reversal measurement technique when combined with the 6220 or 6221 to

enable resistance measurements down to 10 nΩ.

Section 1

Introduction

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1-2 2182A-900-01 Rev. C July 2022

Extended warranty

Additional years of warranty coverage are available on many products. These valuable contracts protect you from unbudgeted service expenses and provide additional years of protection at a fraction of the price of a repair. Extended warranties are available on new and existing products. Contact your local Keithley Instruments office, sales partner, or distributor for details.

Contact information

If you have any questions after you review the information in this documentation, please contact your local Keithley Instruments office, sales partner, or distributor. You can also call the Tektronix corporate headquarters (toll-free inside the U.S. and Canada only) at 1-800-833-9200. For worldwide contact numbers, visit tek.com/en/contact-tek.

Organization of manual sections

The information in this manual is organized into the following major categories:

• Installation: Describes how to turn on the instrument and set up remote communications

interfaces.

• Instrument description: Describes the front-panel and rear-panel components, error and status

messages, and reset.

• Making measurements: Describes how to make test connections and how to make

measurements.

• Measure considerations: Describes how to minimize noise and other unwanted signals that can

adversely affect low-level measurements.

• Delta, pulse delta, and differential conductance: Describes how to use the delta, pulse delta,

and differential conductance features.

• Stepping and scanning: Describes how to use the 2182A for stepping and scanning.

• Reading buffers: Describes how to use the reading buffers.

• Triggering: Describes the front panel and remote triggering options.

• Limits: Describes how to use limits and provides a resistor-sorting application example.

• Maintenance: Contains information about instrument maintenance, including line fuse

replacement and firmware upgrades.

• Introduction to SCPI commands: Describes how to control the instrument using SCPI

commands.

• SCPI command reference: Contains programming notes and an alphabetical listing of all SCPI

commands available for the 2182A.

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• Common commands: Contains descriptions of IEEE Std 488.2 common commands.

• Program examples: Provides code samples.

• Status model: Describes the 2182A status model.

• Model 182 emulation commands: Provides a list of commands for 182 emulation.

• IEEE-488 bus overview: Describes the IEEE-488 bus.

General ratings

The general ratings of the 2182A are listed in the following table.

Instrument power

The 2182A operates from a line voltage of 100 V ac, 120 V ac, 220 V ac, or 240 V ac at line frequencies of 45 Hz to 66 Hz or 360 Hz to 440 Hz.

On power-up, the 2182A detects the line-power frequency and automatically selects the correct frequency setting. You can check the line-power frequency setting by sending the line frequency query:

:SYSTem:LFRequency?

The response message is 50 or 60. The 50 indicates that the line frequency is set for 50 Hz or 400 Hz. 60 indicates that it is set for 60 Hz.

Operating the instrument on an incorrect line voltage may cause damage to the instrument, possibly voiding the warranty.

You must turn on the 2182A and allow it to warm up for at least 2½ hours to achieve rated accuracies.

Section 2

Installation

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2-2 2182A-900-01 Rev. C July 2022

The power cord supplied with the 2182A contains a separate protective earth (safety ground) wire for use with grounded outlets. When proper connections are made, the instrument chassis is connected to power-line ground through the ground wire in the power cord. In the event of a failure, not using a properly grounded protective earth and grounded outlet may result in personal injury or death due to electric shock.

Do not replace detachable mains supply cords with inadequately rated cords. Failure to use properly rated cords may result in personal injury or death due to electric shock.

Changing the line voltage

In most cases, the line voltage is set for the area to which the instrument is shipped and does not need to be changed.

To verify the line voltage setting, look at the window of the fuse holder assembly, as shown in the following figure.

If you need to change the line voltage, use the following instructions.

To change the line voltage:

1. Power off the instrument.

2. Remove all test leads connected to the instrument.

3. Remove the line cord.

4. Place the tip of a flat-blade screwdriver into the power module by the fuse holder assembly.

5. Gently push in and move to the left. Release pressure on the assembly. Its internal spring pushes it out of the power module, as shown in the following figure.

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Figure 1: Fuse and line voltage selector

6. Remove the line voltage selector from the assembly and rotate it to the proper position. When the selector is installed into the fuse holder assembly, the correct line voltage appears in the window.

7. Install the fuse holder assembly into the power module by pushing it in until it locks in place.

Line power connection

To connect the 2182A to line power and turn on the instrument:

1. Check the line voltage setting on the power module. Make sure it is correct for the operating voltage in your area. If not, refer to Changing the line voltage (on page 2-2).

2. Make sure the front-panel power switch is in the off (0) position.

3. Connect the supplied power cord to the ac receptacle on the rear panel.

4. Connect the other end of the power cord to a grounded ac outlet.

5. Turn on the instrument by pressing the front-panel power switch to the on (|) position.

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Power-up sequence

On power-up, the 2182A performs self-tests on its EPROM and RAM, and momentarily lights all digit segments and annunciators. If a failure is detected, the instrument momentarily displays an error message and the ERR annunciator turns on. For a list of error messages, refer to Error messages (on page 11-4).

When the instrument passes the self-tests, the firmware revision levels are displayed. For example:

REV: A01 A02

Where A01 is the main board ROM revision and A02 is the display board ROM revision. After the power-up sequence, the instrument begins to display readings.

Remote communications interfaces

The 2182A supports the following built-in remote interfaces:

• GPIB (IEEE-488) interface

• RS-232 interface

You can use only one interface at a time. At the factory, the GPIB bus is selected. You can select the interface from the front panel. The interface selection is stored in nonvolatile memory, so it does not change if power was off or after a remote interface reset. When you enable the GPIB interface, the RS-232 interface is disabled. Conversely, when you enable the RS-232 interface, the GPIB interface is disabled.

When the interface is changed, all data in the buffer clears.

Programming languages

The 2182A supports the Standard Commands for Programmable Instrument (SCPI) programming language or the 182 programming language.

SCPI is fully supported by the GPIB and RS-232 interfaces. Always calibrate the 2182A using the SCPI language.

The 182 language is only available with GPIB communications. It implements most commands (DDCs) that are available in the Keithley Model 182 Sensitive Digital Voltmeter. The commands and the programming limitations are provided in Model 182 emulation commands (on page 17-1).

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RS-232 connections

The RS-232 serial port is connected to the serial port of a computer using a straight-through RS-232 cable terminated with DB-9 connectors. The serial port uses the transmit (TXD), receive (RXD), and signal ground (GND) lines of the RS-232 standard. It does not use the hardware handshaking lines CTS and RTS.

If your computer uses a DB-25 connector for the RS-232 interface, you need a cable or adapter with a DB-25 connector on one end and a DB-9 connector on the other, wired straight through. Do not use a null modem cable. The following figure shows the pins and the following tables provide pinout identification for the 9-pin (DB-9) connector or 25-pin (DB-25) serial port connector on the computer.

Figure 2: RS-232 interface connector

Pinouts for the RS-232 connector

Description

No connection

TXD, transmit data

RXD, receive data

No connection

GND, signal ground

No connection

RTS, ready to send

CTS, clear to send

No connection

Pinouts for the DB-25 computer serial port

Signal

DB-9 pin number

DB-25 pin number

DCD, data carrier detect

1 8 RXD, receive data

2 3 TXD, transmit data

3 2 DTR, data terminal ready

GND, signal ground

DSR, data set ready

6 6 RTS, request to send

7 4 CTS, clear to send

8 5 RI, ring indicator

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The following figure shows the rear-panel connections for the RS-232 interface.

Figure 3: RS-232 connections

RS-232 interface selection and configuration

The RS-232 interface is selected and configured from the RS-232 menu. From this menu, you can enable or disable the RS-232 interface, and check or change the following settings:

• Baud rate (192,000, 9600, 4800, 2400, 1200, 600, or 300)

• Flow control (none or Xon/Xoff)

• Terminator (CR, LF, CRLF, or LFCR)

The RS-232 interface transfers data using eight data bits, one stop bit, and no parity. Make sure the controller you connect to the 2182A also uses these settings.

Make sure that the terminal that you are connecting to the 2182A can support the baud rate you select. Both the 2182A and the other device must be configured for the same baud rate.

You can break data transmissions by sending a ^C or ^X character string to the controller. This clears any pending operation and discards any pending output.

For the RS-232 interface, you can only use the SCPI language to program the instrument. The instrument automatically switches to the SCPI language when the RS-232 interface is enabled.

To retain a present RS-232 setting, press ENTER with the setting displayed. You can exit from the menu structure at any time by pressing EXIT.

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To select and configure the RS-232 interface:

1. Press SHIFT and then RS232 to access the RS-232 menu. The present state (ON or OFF) of the RS-232 is displayed.

2. To enable the RS-232 interface, place the cursor on the on/off selection by pressing the ► key.

3. Press the ▲ or ▼ key to toggle the selection to ON.

4. Press ENTER. The present baud rate is displayed.

5. To change baud rate, place the cursor on the baud rate value.

6. Use the ▲ and ▼ keys to display the correct baud rate value.

7. Press ENTER. The present flow control setting is displayed.

8. To change flow control setting, place the cursor on the present flow control selection.

9. Press the ▲ or ▼ key to toggle the selection.

10. Press ENTER. The present terminator is displayed.

11. To change the terminator, place the cursor on the present terminator selection.

12. Press the ▲ or ▼ key to display the correct terminator. You can select:

▪ LF: Line feed ▪ CR: Carriage return ▪ LFCR: Line feed, carriage return ▪ CRLF: Carriage return, line feed

13. Press ENTER. The instrument returns to the normal display.

Flow control (signal handshaking)

Signal handshaking between the controller and the instrument allows the two devices to indicate being ready or not ready to receive data. The 2182A does not support hardware flow control.

Software flow control is in the form of X_ON and X_OFF characters and is enabled when XonXoFF is selected from the RS232 FLOW menu. When the input queue of the 2182A becomes more than 3/4 full, the instrument issues an X_OFF command. The control program responds to this and stops sending characters until the 2182A issues the X_ON, which it does when its input buffer has dropped below half-full.

The 2182A recognizes X_ON and X_OFF sent from the controller. An X_OFF causes the 2182A to stop outputting characters until it sees an X_ON. Incoming commands are processed after the <CR> character is received from the controller.

If NONE is the selected flow control, there is no signal handshaking between the controller and the 2182A. Data will be lost if it is transmitted before the receiving device is ready.

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For RS-232 operation, use *OPC or *OPC? with commands that respond slowly. Refer to *OPC (on page 14-7) for detail on the command and a list of the slowest responding commands.

GPIB setup

The following topics contain information about GPIB standards, bus connections, and primary address selection.

The 2182A GPIB interface is IEEE Std 488.1 compliant and supports IEEE Std 488.2 common commands and status model topology.

You can have up to 15 devices connected to a GPIB interface, including the controller. The maximum cable length is the lesser of either:

• The number of devices multiplied by 2 m (6.5 ft)

• 20 m (65.6 ft)

You may see erratic bus operation if you ignore these limits.

Install the GPIB driver software

Check the documentation for your GPIB controller for information about where to acquire drivers. Keithley Instruments also recommends that you check with the manufacturer of the GPIB controller for the latest version of drivers or software.

It is important that you install the drivers before you connect the hardware. This prevents associating the incorrect driver to the hardware.

Install the GPIB cards in your computer

Refer to the documentation from the GPIB controller manufacturer for information about installing the GPIB controllers.

GPIB bus connections

To connect a 2182A to the GPIB interface, use a cable equipped with standard GPIB connectors, as shown in the following figure.

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Figure 4: GPIB connector

To allow many parallel connections to one instrument, stack the connectors. Each connector has two screws on it to ensure that connections remain secure. The following figure shows a typical connection diagram for a test system with multiple instruments.

The 2182A GPIB connector has metric threads. Do not use GPIB connectors with non-metric screws.

To avoid possible mechanical damage, stack no more than three connectors on any one instrument.

Figure 5: Typical connection diagram for a test system with multiple instruments

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To minimize interference caused by electromagnetic radiation, use only shielded IEEE-488 cables, such as the Keithley Instruments Model 7007-1 Shielded GPIB Cable.

To connect the 2182A to the IEEE-488 bus:

1. Line up the cable connector with the connector on the rear panel. The rear-panel connection is shown in the following figure.

Figure 6: IEEE-488 connector location

2. Tighten the screws securely, making sure not to overtighten them.

3. Make sure that the other end of the cable is properly connected to the controller. See the instruction manual for your controller for information about properly connecting to the IEEE-488 bus.

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GPIB interface selection and configuration

The GPIB interface is selected and configured from the GPIB menu structure. From this menu, you can enable or disable the GPIB interface, and check or change the following settings:

• Primary address (0 to 30)

• Language (SCPI or 182)

The default GPIB address is 07. You can set the address from 1 to 30 if it is unique in the system. This address cannot conflict with an address that is assigned to another instrument or to the GPIB controller.

GPIB controllers are usually set to 0 or 21. To be safe, do not configure any instrument to have an address of 21.

The instrument saves the address in nonvolatile memory. It does not change when you send a reset command or when you turn the power off and on again.

You can use either the SCPI or 182 language to program the instrument when using a GPIB connection.

To retain a present GPIB setting, press ENTER with the setting displayed. You can exit from the menu structure at any time by pressing EXIT.

To enable the GPIB interface, change the GPIB address, and change the programming language:

1. Press SHIFT and then GPIB to access the GPIB menu. The present state (on or off) of the GPIB is displayed.

2. Place the cursor on the on/off selection by pressing the ► key.

3. Press the ▲ or ▼ key to toggle the selection to ON.

4. Press ENTER. The present GPIB address is displayed.

5. Use the ◄, ►, ▲, and ▼ keys to display a valid address value.

6. Press ENTER. The present programming language selection is displayed.

7. Place the cursor on the present language selection.

8. Press the ▲ and ▼ key to toggle the selection.

9. Press ENTER. The instrument returns to the normal display state.

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Front-panel GPIB operation

The following paragraphs describe aspects of the front panel that are part of GPIB operation, including messages, status indicators, and the LOCAL key.

GPIB status indicators

The REM (remote), TALK (talk), LSTN (listen), and SRQ (service request) annunciators show the GPIB bus status.

The REM indicator is on when the instrument is in the remote state. The instrument must be addressed to listen with REM true before the REM indicator turns on. When the instrument is in the remote state, all front-panel keys except for the LOCAL key are locked out. When REM is turned off, the instrument is in the local state, and front-panel operation is restored.

The TALK indicator is on when the instrument is in the talker active state. To place the instrument in the talk state, address it to talk with the correct MTA (My Talk Address) command. TALK is off when the instrument is in the talker idle state. To place the instrument in the talker idle state, send an UNT (Untalk) command, address it to listen, or send the IFC (Interface Clear) command.

The LSTN indicator is on when the 2182A is in the listener active state, which is activated by addressing the instrument to listen with the correct MLA (My Listen Address) command. LSTN is off when the instrument is in the listener idle state. To place the instrument in the listener idle state, send UNL (Unlisten), address it to talk, or send the IFC (Interface Clear) command over the bus.

When the SRQ indicator is on, a service request was generated. You can program the instrument to generate a service request (SRQ) when one or more errors or conditions occur. This indicator stays on until the serial poll byte is read or all the conditions that caused the SRQ have ended.

LOCAL key

The LOCAL key cancels the remote state and restores local operation of the instrument. Pressing the LOCAL key also turns off the REM indicator and returns the display to normal if a user-defined message was displayed.

If the LLO (Local Lockout) command is in effect, the LOCAL key is inoperative. Refer to LLO (on page 2-15) for additional information.

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General bus commands

General commands are commands that have the same general meaning, regardless of the instrument. The following table lists the general bus commands.

Command

Effect on 2182A

DCL

Device clear. Returns the 2182A and all devices on the GPIB to known conditions. See DCL (on page 2-13) for details.

GET

Group execute trigger. Initiates a trigger. See GET (on page 2-13) for details.

GTL

Go to local. Cancel remote; restore 2182A front-panel operation. See GTL (on page 2-14) for details.

IFC

Interface clear. Goes into talker and listener idle states. See IFC (on page 2-14) for details.

LLO

Local lockout. LOCAL key locked out. See LLO (on page 2-15) for details.

REN

Remote enable. Goes into remote operation when next addressed to listen. See REN (on page 2-15) for details.

SDC

Selective device clear. Returns the 2182A to known conditions. See SDC (on page 2-15) for details.

SPE, SPD

Serial polling. Serial polls the 2182A. See SPE, SPD (on page 2-16) for details.

DCL (device clear)

Use the device clear (DCL) command to clear the GPIB interface and return it to a known state. The DCL command is not an addressed command, so all instruments equipped to implement DCL are returned to a known state simultaneously.

When the 2182A receives a DCL command, it:

• Clears the input buffer, output queue, and command queue

• Cancels deferred commands

• Clears any command that prevents the processing of any other device command

The DCL command does not affect instrument settings and stored data. Program fragment

CALL TRANSMIT ("DCL", status%) ' Clears all devices.

GET (group execute trigger)

The group execute trigger (GET) command is a GPIB trigger that triggers the instrument to make readings from a remote interface. The 2182A reacts to this trigger if it is the programmed control source. The control source is programmed from the SCPI TRIGger subsystem.

With the instrument programmed and waiting for a GPIB trigger, the following program fragment provides the GET.

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Program fragment

CALL TRANSMIT ("UNL LISTEN 7 GET", status%) ' Trigger 2182A over

the bus.

When the command is executed, the trigger event for the 2182A occurs. Any other listeners ignore the trigger.

GTL (go to local)

Use the go to local (GTL) command to put an instrument that is in remote mode instrument into local mode. Leaving the remote state also restores operation of all front-panel controls. The following program fragment demonstrates how to use GTL.

Program fragment

CALL TRANSMIT ("UNL LISTEN 7 GTL", status%)' Place 2182A in local mode.

IFC (interface clear)

The controller sends the interface clear (IFC) command to place the 2182A in the talker idle state and the listener idle state. The instrument responds to the IFC command by canceling illumination of the front-panel TALK or LSTN lights if the instrument was previously placed in one of these states.

Transfer of command messages to the instrument and transfer of response messages from the instrument are not interrupted by the IFC command. If transfer of a response message from the instrument was suspended by IFC, transfer of the message resumes when the instrument is addressed to talk. If transfer of a command message to the instrument was suspended by the IFC command, the rest of the message can be sent when the instrument is addressed to listen.

This command does not affect the status of the instrument. Settings, data, and event registers are not changed.

To send the IFC command, the controller needs to set the IFC line true for a minimum of 100 μs. The initialize routine (CALL INITIALIZE) uses this command internally. This command does not

affect the status of the instrument. Settings, data, and event registers are not changed. To send the IFC command, the controller must set the IFC line true for a minimum of 100. Program fragment

CALL INITIALIZE (21, 0) ' Initialize GPIB system (sends IFC) and set ' interface card address to 21.

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LLO (local lockout)

Use the LLO command to prevent local operation of the instrument. After the 2182A receives LLO, all its front-panel controls except the POWER switch are inoperative. In this state, pressing LOCAL does not restore control to the front panel. The GTL command restores control to the front panel.

Program fragment

CALL TRANSMIT ("UNL LISTEN 7 LLO", status%)' Lock out front panel. CALL TRANSMIT ("UNL LISTEN 7 GTL", status%)' Restore front panel.

REN (remote enable)

When the instrument detects the remote enable (REN) event, it is set up for remote operation. The instrument is not placed in remote mode when it detects the REN event. The instrument must be addressed to listen after the REN event before it goes into remote mode.

You should place the instrument into remote mode before you attempt to program it using a remote interface.

The instrument does not have to be in remote to be a talker.

All front-panel controls except for LOCAL and POWER are inoperative while the instrument is in remote. To restore normal front-panel operation, press the LOCAL key.

Program fragment

CALL TRANSMIT ("MTA LISTEN 7 REN", status%) ' Place 2182A in remote;

' turn on REM annunciator.

SDC (selective device clear)

The selective device clear (SDC) command is an addressed command that performs essentially the same function as the device clear (DCL) command. However, because each device must be individually addressed, the SDC command provides a method to clear only selected instruments, instead of clearing all instruments simultaneously with the DCL command.

When the 2182A receives an SDC command, it:

• Clears the input buffer, output queue, and command queue

• Cancels deferred commands

• Clears any command that prevents the processing of any other device command

An SDC call does not affect instrument settings and stored data. Program fragment

CALL TRANSMIT ("UNL LISTEN 7 SDC", status%) ' Clears 2182A.

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SPE, SPD (serial polling)

Use the serial polling sequence to obtain the 2182A serial poll byte. The serial poll byte contains important information about internal functions. Generally, the serial polling sequence is used by the controller to determine which of several instruments has requested service with the SRQ line. The serial polling sequence may be performed at any time to obtain the status byte from the 2182A. For more information, see Status Byte Register overview (on page 16-2).

Program fragment

WaitSRQ: CALL SPOLL (7, poll%, status%) ' Serial poll the 2182A. IF (poll% AND 64) = 0 THEN GOTO WaitSRQ ' Loop back if no SRQ.

Transmit routines

A transmit routine sends general bus commands. It contains a series of GPIB commands to be carried out. In addition to the general bus commands, there are other commands used in the transmit command string. For detail on all the commands, refer to the documentation for the interface card. Some of the more frequently used commands are:

• UNL: Unlisten disables any listeners that may exist.

• UNT: Untalk disables the current talker, if any.

• LISTEN 7: Listen assigns the device at address 7 (2182A) to be a listener.

• MTA: My Talk Address assigns the computer as the talker.

In this section:

Front-panel overview ................................................................3-1

Rear-panel overview .................................................................3-5

Error and status messages .......................................................3-6

Default settings .........................................................................3-7

Reset the instrument .................................................................3-9

Setting the number of displayed digits ......................................3-9

Front-panel overview

The front panel of the 2182A is shown in the following figure.

Figure 7: Model 2182A front panel

Most keys perform two functions. The label on a key indicates its normal function, which is selected by pressing the key. The label above a key indicates its shifted function. A shifted function is selected by pressing the SHIFT key and then the function key.

Section 3

Instrument description

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1 Display annunciators

The display of the 2182A is primarily used to display readings with the units and type of measurement. Annunciators are at the top, bottom, left, and right of the reading or display message. The annunciators indicate various states of operation, as described in the following table.

Readings are being stored in the buffer

Additional selections are available

Beeper is on for limit testing

AUTO

Autorange is enabled

BUFFER

Readings that are stored in the buffer are being recalled

CH1

Channel 1 input is displayed

CH2

Channel 2 input is displayed

CH1 and CH2

Ratio (V1/V2) reading is displayed

ERR

Questionable reading or invalid calibration step

FAST

Fast (0.1 PLC) reading rate is selected

FILT

Filter is enabled

HOLD

Instrument is in hold mode

LSTN

Instrument is addressed to listen over GPIB

MATH

Calculation (mx+b or percent (%)) is enabled

MED

Medium (1 PLC) reading rate is selected

REAR

Analog output is on

REL

Relative offset is enabled for the present measurement function

REM

Instrument is in GPIB remote mode

SCAN

Scan mode is selected

SHIFT

SHIFT is selected

SLOW

Slow (5 PLC) reading rate is selected

SRQ

Service request over GPIB

STAT

Buffer statistics are displayed

STEP

Step mode is selected

TALK

Instrument addressed to talk over GPIB bus

TIMER

Timer controlled scans are in use

TRIG

External triggering (front panel, bus, or Trigger Link) is selected

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2 SHIFT key, LOCAL key, and POWER switch

SHIFT

Use to select a shifted function or operation

LOCAL

Cancels GPIB remote mode Controls keyclicks; press SHIFT then LOCAL to enable or disable keyclicks

POWER

Power switch; when pressed in, 2182A is on; when out, 2182A is off

3 Function keys

Top row of keys

Unshifted

DCV1

Selects the Channel 1 voltage measurement function

DCV2

Selects the Channel 2 voltage measurement function

V1/V2

Selects ratio (Channel 1 voltage reading / Channel 2 voltage reading)

ACAL

Selects automatic gain calibration

FILT

Enables or disables the filter for the selected measurement function

REL

Enables or disables the relative offset for the selected measurement function

TEMP 1

Selects the Channel 1 temperature measurement function; when the internal sensor is selected, TEMP 1 measures and displays the internal temperature of the 2182A

TEMP 2

Selects the Channel 2 temperature measurement function; when the internal sensor is selected, TEMP 2 measures and displays the internal temperature of the 2182A

Shifted

MX+B

Multiplies a scale factor (M) to the reading (X) and then adds an offset (B)

Calculates the percent deviation from a specified reference

1 − V2

Selects the delta; (V

t1 − V

t2)/2

LSYNC

Enables or disables line cycle synchronization; when enabled, noise induced by the power line is reduced at the expense of speed

TYPE

Selects the filter (analog or digital) and configures the digital filter (window, count and type)

OUTPUT

Enables or disables the relative offset for the analog output

OUT

Enables or disables the analog output

TCOUPL

Configure the temperature measurement (units, junction type, thermocouple type, and sensor type)

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Middle row of keys

Unshifted

EX TRIG

Selects an external trigger source (front panel, bus, or Trigger Link)

TRIG

Triggers a measurement from the front panel

STORE

Sets the reading count for the buffer and enables the buffer

RECALL

Displays the stored readings (including maximum, minimum, peak-to-peak, average, and standard deviation)

The ▲ and ▼ range keys scroll through the buffer and the ◄ | ► key toggles

between reading number and reading

VALUE

Sets the upper and lower limits for limit testing

ON/OFF

Enables or disables limit testing and selects the beeper mode for limit testing

◄ | ►

Controls the cursor position for making selections or editing values

Shifted

DELAY

Sets the user delay between the trigger and the measurement

HOLD

Holds reading when the specified number of samples is in the selected tolerance

Bottom row of keys

Unshifted

STEP

Steps through the channels; sends a trigger after each channel

SCAN

Scans through the channels; sends a trigger after last channel

SAVE

Saves the present configuration for the power-on user default

RESTR

Restores the factory or user default configuration

DIGITS

Changes the number of digits of reading resolution

RATE

Changes the reading rate (the number of power line cycles (PLC))

EXIT

Cancels the selection or returns to the measurement display

ENTER

Accepts the selection, moves to the next choice, or returns to the measurement display

Shifted

CONFIG

Configures a scan (type, timer, channel count, and reading count)

HALT

Turns off step/scan operation

GPIB

Enables or disables the GPIB interface, sets the GPIB address, and selects the language

RS232

Enables or disables the RS-232 interface and selects the baud rate, flow control, and terminator

CAL

Accesses calibration

TEST

Tests the display annunciators, display digit segments, and front-panel keys. For

more detail on these options, refer to “Front panel tests” in the Model 2182A Service Manual.

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4 Range keys

▲

Selects the next higher voltage measurement range

▼

Selects the next lower voltage measurement range

AUTO

Enables or disables autorange

5 Handle

Pull out and rotate to new position.

6 Input connector

CHANNEL 1

Measure voltage or temperature; voltage ranges are 10 mV, 100 mV, 1 V, 10 V, and 100 V

CHANNEL 2

Measure voltage or temperature; voltage ranges are 100 mV, 1 V, and 10 V

Rear-panel overview

The rear panel of the 2182A is shown in the following figure.

Figure 8: 2182A rear panel

1 ANALOG OUTPUT

The analog output provides a scaled non-inverting dc voltage that is typically used to drive a chart recorder. With analog output gain set to one, a full range input results in a 1.2 V analog output. For additional detail on using the analog output, refer to Analog output overview (on page 4-34).

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2 TRIGGER LINK

An eight-pin micro-DIN connector for sending and receiving trigger pulses among connected instruments. Use a trigger link cable or adapter, such as Keithley Models 8501-1, 8502, or 8503.

The pinouts for the TRIGGER LINK connector are shown in the following figure.

Figure 9: TRIGGER LINK pinouts

3 RS-232

Connector for RS-232 operation. Use a straight-through (not null modem) DB-9 shielded cable.

4 IEEE-488

Connector for IEEE-488 (GPIB) operation. Use a shielded cable, such as the Model 7007-1.

5 Power module

Contains the ac line receptacle, power-line fuse, and the line-voltage setting. You can configure the instrument for line voltages of 100 V ac, 120 V ac, 220 V ac, or 240 V ac at line frequencies of 45 Hz to 66 Hz or 360 Hz to 440 Hz. If you need to change the line voltage, refer to Changing the line

voltage (on page 2-2).

Error and status messages

See Status and error messages (on page 11-4) for a list of error and status messages. You can program the instrument to generate an SRQ and send command queries to check for

specific error conditions. Refer to Program examples (on page 15-1).

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Default settings

The default setup configurations are factory and user. As shipped from the factory, the 2182A powers up to the factory default settings listed in the following table. You can also set the 2182A to power up to a user default setup. The user default setup contains the last configuration you saved. The SAVE key saves the present configuration as the user default setup. The RESTR key restores the instrument to the factory defaults or the user-saved defaults.

To assure that the proper filter state is recalled, set the analog and digital filters before saving the user setup. Refer to Filters (on page 4-20) for more information.

To save the present setup as the power-on default:

1. Configure the instrument for your measurement application.

2. Press the SAVE key.

3. Press the ▼ and ▲ keys to display YES or NO.

4. Press the ENTER key to store the settings.

To restore factory or user settings:

1. Press the RESTR key.

2. Press the ▼ and ▲ keys to select FACT (factory) or USER.

3. Press the ENTER key to restore the settings.

Default settings

Setting

Factory Default

Measure function

Voltage

Analog output

Gain (M)

1.0

Offset (B)

Relative (REL)

Off

Front Autozero

Autozero

LSYNC

Off

Buffer

No effect

Delta

Off

Function

DCV1

GPIB

No effect (On at factory)

Address

No effect (7 at factory)

Language

No effect (SCPI at factory)

Key click

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Default settings

Setting

Factory Default

Limits

Off

Beeper

Never

High limit 1

Low limit 1

−1

High limit 2

Low limit 2

−2

mx+b

Off

Scale factor (M)

1.0

Offset (B)

0.0

Percent (%)

Off

Reference

1.0

Ratio (V1/V2)

Off

RS-232

Off

Baud rate

No effect

Flow control

No effect

Terminator (Tx)

No effect

Scanning

Off

Type

Internal

Timer

Off

Channel 1 count

Reading count

TEMP 1 and TEMP 2

Digits

Filter

Analog filter

Off

Digital filter

Count

Mode

Moving average

Window

0.01%

Rate

5 PLC (Slow)

Reference junction

Internal

Relative (REL)

Off

Sensor

Thermocouple

Thermocouple type

Type J

Units

Triggers

Continuous

Delay

Auto

Control Source

Immediate

DCV1 and DCV2

Digits

7.5

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Default settings

Setting

Factory Default

Filter

Analog filter

Off

Digital filter

Count

Mode

Moving average

Window

0.01%

Hold

Off

Count

Window

Range

Auto

Rate

5 PLC (Slow)

Relative (REL)

Off

Reset the instrument

You can reset many of the instrument settings to their default values. For detail on what gets reset, see Default settings (on page 3-7) and the descriptions in SCPI command reference (on page 13-1).

To reset the instrument using a remote interface, send the command *RST.

Setting the number of displayed digits

You can change the number of digits that are displayed for voltage and temperature measurement readings on the display. For voltage readings, you can display 3½, 4½, 5½, 6½, or 7½ digits. For temperature readings, you can display 4 to 7 digits.

The number of displayed digits does not affect accuracy or speed of the measurements. It also does not affect the format of readings that are returned from a remote command.

The digits setting for a voltage function applies to the other voltage function. For example, if you set DCV1 for 5½ digits, DCV2 is also set for 5½ digits. Similarly, the digits setting for a temperature function applies to the other temperature function. Setting TEMP 1 for 6 digits also sets TEMP 2 for 6 digits.

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To set the number of displayed digits from the front panel:

1. Press the DCV1, DCV2, TEMP 1, or TEMP 2 key.

2. Press the DIGITS key until the correct number of digits is displayed.

This setting takes effect the next time you make a measurement.

From a remote interface:

Refer to :SENSe:<function>:DIGits (on page 13-41).

In this section:

Measurement overview .............................................................4-1

Warm-up ...................................................................................4-3

ACAL (calibration) .....................................................................4-3

Test connections .......................................................................4-5

Measuring voltage and temperature .......................................4-14

Range .....................................................................................4-15

Autozero modes ......................................................................4-17

Rate ........................................................................................4-19

Filters ......................................................................................4-20

Relative offset .........................................................................4-25

Pumpout current (low charge injection mode) .........................4-27

Line cycle synchronization ......................................................4-27

Calculations that you can apply to measurements ..................4-28

Ratio .......................................................................................4-31

Analog output ..........................................................................4-34

Applications .............................................................................4-37

Measurement overview

The 2182A provides two input channels for dc voltage and temperature measurements, as shown in the following table.

Measurement

Input Channels to Use

Voltage

Channel 1

Temperature

Channel 1

Voltage and Voltage

Channel 1 and Channel 2

Voltage and Temperature

Channel 1 and Channel 2

Channel 1 is used as the fundamental measurement channel, while Channel 2 provides sense measurements. Because of this operational relationship between the two channels, Channel 2 cannot be used as an independent, stand-alone measurement channel. Its inputs must be referenced to Channel 1 LO.

Section 4

Making measurements

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Using the front-panel display

Guidelines for making menu selections:

• The display shows the presently selected option with each menu item. For example, if °C is the

present units option, then UNITS: C is displayed.

• Blinking characters indicate cursor position. The cursor can be on a menu item name (for

example, UNITS is blinking) or on a menu item option (for example, C is blinking). Cursor position is controlled by the ◄ and ► keys.

• With the cursor on a menu item name, you can use the ▲ or ▼ key to scroll through the other

menu items. Press ENTER to select the displayed option and move on to the next menu item or exit if you are at the end of the menu.

• With the cursor on a menu item option, you can use the ▲ or ▼ key to display one of the other

options for that menu item. Press ENTER to select the displayed option and move to the next menu item or exit if you are at the end of the menu.

• Press EXIT to leave the menu and return to the normal display state.

Voltage measurements

The 2182A has the voltage measurement functions DCV1 and DCV2. DCV1 is available for input Channel 1 and DCV2 is available for Channel 2.

DCV1 has five measurement ranges (10 mV, 100 mV, 1 V, 10 V, and 100 V) and can measure voltage from 1 nV to 120 V. DCV2 (Channel 2) has three measurement ranges (100 mV, 1 V, and 10 V) and can measure voltage from 10 nV to 12 V. Accuracy for each channel is listed in the specifications, available at tek.com/keithley.

Temperature measurements

The 2182A has the temperature measurement functions TEMP 1 and TEMP 2. TEMP 1 is available for input Channel 1 and TEMP 2 is available for Channel 2.

Depending on which thermocouple type is used (B, E, J, K, N, R, S, or T), the 2182A can measure temperature from −200 °C to 1820 °C. Refer to the 2182A specifications for the measurement range for each thermocouple type. The specifications are available at tek.com/keithley.

To make accurate temperature measurements, the thermocouple connections (reference junctions) must be maintained at a known temperature. You can use the internal reference junction or an external simulated reference junction.

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The internal reference junction of the 2182A is the input connector. A temperature sensor is inside the instrument, adjacent to the input connector. The sensor is measured continuously to maintain accuracy. To use the internal reference junction, the thermocouple wires must be soldered directly to a connector that mates to the input connector. A disadvantage of using the internal reference junction is the connection requirement. You cannot use the supplied 2107 input cable as is. You must modify the cable or use a separate connector.

You can use a simulated reference junction, which is an external apparatus, such as an ice bath, as the reference junction. The thermocouple wires are connected to the copper lugs of the supplied input cable. The connection points are then immersed in the ice bath. The temperature of the ice bath must be entered into the 2182A as the simulated reference temperature.

Warm-up

After the 2182A is turned on, it must be allowed to warm up for at least 2½ hours to allow the internal temperature to stabilize. After the warm-up period, an automatic calibration (ACAL) must be performed if the present internal temperature and the last internal temperature reading differ by more than 1°C.

ACAL (calibration)

Autocalibration (ACAL) is a special front-end gain calibration for the 10 mV and 100 V ranges. It needs to be performed whenever the internal temperature and TCAL vary by more than 1 °C. TCAL is the internal temperature reading at the time of the last ACAL. For example, if ACAL was performed at 28 °C and the internal temperature changes to 29.1 °C, another ACAL is required to maintain the specified accuracy.

When the internal temperature and TCAL differ by more than 1 °C, bit 9 in the Questionable Event Condition Register is set to indicate a questionable ACAL. See Status model (on page 16-1) for more information.

You can perform a full or low-level ACAL. FULL ACAL calibrates the 10 mV and 100 V ranges, while LOW-LVL (low-level) ACAL only calibrates the 10 mV range. If you are not going to use the 100 V range, it is recommended that you perform LOW-LVL ACAL.

FULL ACAL requires that no connectors or cables are connected to the input connector on the front panel of the 2182A. Whenever input connections are broken for an extended time, the contacts must be cleaned before reconnecting. See Cleaning input connectors (on page 11-1).

For LOW-LVL ACAL, you do not need to remove the input cable, break any connections, or remove power.

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ACAL is a partial calibration that can be performed by the user. For complete instrument calibration, which must be performed by a qualified service technician, refer to the Model 2182A Service Manual.

It takes about five minutes to complete low-level ACAL and a little more than five minutes to complete full ACAL. When finished, the instrument returns to the normal display state.

To perform LOW-LVL or FULL ACAL from the front panel:

1. Press the ACAL key to access the menu.

2. Use the ▼ or ▲ key to display the type of ACAL (LOW-LVL or FULL).

3. Press ENTER. The message ACAL is displayed while calibration is in process.

To perform LOW-LVL or FULL ACAL using remote commands:

Refer to the CALibration subsystem (on page 13-26) for command descriptions and examples.

Measuring internal temperature

To measure the internal temperature of the 2182A:

1. Press SHIFT and then TCOUPL to display the present units designator (C, F, or K) for temperature measurements.

2. To change the units designator, press the ► key to place the blinking cursor on the units designator, and press the ▼ or ▲ key to display the units.

3. Press ENTER. The present sensor selection (TCOUPLE or INTERNL) is displayed.

4. To change the sensor selection, press the ► key to place the blinking cursor on TCOUPLE and press the ▼ or ▲ key to display INTERNL.

5. Press ENTER to return to the normal display state.

6. Press TEMP 1 or TEMP 2 to measure and display the internal temperature of the 2182A. When the internal temperature is displayed, the CH1 and CH2 annunciators are off.

Checking TCAL temperature

To determine the internal temperature at the time of the last ACAL:

1. Press SHIFT and then CAL to access the calibration menu.

2. Use ▼ or ▲ key to display CAL: TEMP.

3. Press ENTER. The temperature (in °C) at the time of the last ACAL is displayed.

4. Use the EXIT key to return to the measurement display.

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Test connections

A hazardous voltage condition exists at or above 42 V

PEAK

. To prevent electric shock that could result in injury or death, never make or break connections while hazardous voltage is present.

Exceeding the following limits may cause instrument damage that will void the warranty:

▪

Channel 1 HI and LO inputs have a maximum measurement capability of 120 V

PEAK

. These

inputs are protected to 150 V

PEAK

to any terminal or 350 V

PEAK

to chassis.

▪

Channel 2 HI and LO inputs have a maximum measurement capability of 12 V

PEAK

Channel 2 HI is protected to 150 V

PEAK

to any terminal. Channel 2 LO is protected to

70 V

PEAK

to Channel 1 LO. Both inputs are protected to 350 V

PEAK

to chassis.

As a general rule, use Channel 1 whenever possible to measure voltages below 1 V. If you are using Channel 2 to measure voltages below 1 V and the impedance between Channel 2 LO and Channel 1 LO is ≥100 kΩ, pumpout current may be high enough to corrupt measurements. In this case, you can enable the low charge injection mode to reduce pumpout current. Refer to Pumpout current (low

charge injection mode) (on page 4-27) for details.

Connection techniques

Use copper-to-copper connections wherever possible in the test circuit to minimize thermal EMFs that could corrupt measurements.

Any solder connections to your test circuit require the use of silver solder to minimize thermal EMFs.

Silver solder has a high melting point. Take care not to damage a CHANNEL connector (or any other device) by applying excessive heat.

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Model 2107 input cable

The Model 2107 Input Cable, shown in the following figure, is terminated with a CHANNEL connector on one end and copper lugs on the other end. The cable is shielded to chassis ground when connected to the 2182A. You can use this cable to make voltage measurements and temperature measurements that use an external simulated reference junction.

Figure 10: Model 2107 input cable

To make voltage connections, clamp the cleaned copper lugs of the cable to the cleaned copper connectors of the test circuit. For the test circuit, use clean #10 copper bus wire wherever possible. Clean copper-to-copper connections minimize thermal EMFs, which could corrupt a measurement. See Cleaning test circuit connectors (on page 4-13).

If necessary, you can cut the copper lugs off the Model 2107 and connect the wires directly to your test circuit, as described in Customized connections (on page 4-7).

To make temperature (simulated reference) measurements using an external simulated reference junction, wrap or clamp the thermocouple wires around the copper lugs or bare wires of the input cable.

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Customized connections

Temperature measurements using the internal reference junction require that the thermocouple wires be soldered directly to a connector that mates to the input of the 2182A. Use silver solder to minimize thermal EMFs. The following figure shows terminal identification for a connector.

Figure 11: CHANNEL connector - terminal identification

To make these customized connections, you can modify the supplied input cable.

Silver solder has a high melting point. Do not apply excessive heat to the connector. Excessive heat can damage the connector.

Voltage only connections

You can perform single or dual channel voltage measurements. The dual channel feature of the 2182A allows you to make comparison measurements in a test circuit. The connections for voltage measurements are described in the following topics.

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Single channel measurement connections

The following figures show typical connections to measure a DUT using a single channel.

Figure 12: Single-channel voltage connections for Channel 1

When using Channel 2, its inputs must be referenced to Channel 1 LO, as shown in the following figure.

Figure 13: Single-channel voltage connections for Channel 2

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Dual-channel measurement connections

The following figure shows typical connections to make comparison measurements of two devices in a test circuit. For this measurement configuration, there is no voltage differential between the two measurement channels. Channel 2 HI is connected directly to Channel 1 LO.

Figure 14: Typical dual-channel voltage connections

The following figure shows a measurement configuration that has a voltage differential between two channels. The differential is the 2 V drop across R. Channel 1 measures voltage across DUT 1. Channel 2 measures voltage across DUT 2. Internally, the A/D converter references the Channel 2 measurements to Channel 1 LO. For example, if 1 V is being input to Channel 2 and there is a 2 V differential between the two channels, 3 V is applied to the A/D converter. Therefore, if Channel 2 is on the 1 V range, the 3 V applied to the A/D converter causes it to overflow. The 1 V measurement on Channel 2 can only be made on the 10 V range.

Figure 15: Differential dual-channel voltage connections

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When measuring with a voltage differential between two channels, Channel 2 HI or LO cannot be more than 12 V

PEAK

from Channel 1 LO.

Channel voltage differential reduces the maximum measurement capability of Channel 2. Normally, Channel 2 can measure up to 12 V. However, a 2 V differential reduces the maximum measurement capability of Channel 2 to 10 V. In the “Typical dual-channel voltage connections” figure above, a >10 V input to Channel 2 causes an overflow condition.

Measurement techniques

Techniques used to measure resistances in the normal range are not generally suitable for making low-resistance measurements because of errors caused by voltage drops across the test leads. To overcome these limitations, low resistance measurements are usually made using the 4-wire (Kelvin) connections shown in the following figure.

Figure 16: 4-wire low-resistance measurement technique

A current source forces the current (I) through an unknown resistance, developing a voltage across that device. Even though the test lead resistance, R

LEAD

, is present, it does not affect the current

through R

DUT

because I is assumed to be a constant current source with high output impedance. Also, since the voltmeter has a very high input resistance (very low leakage current), the current through the sense leads is negligible and the voltage drop across R

LEAD

is essentially zero. Thus, the voltage

measured by the meter is essentially the same as the voltage across the unknown resistance, R

DUT

Since the current through the measured resistance and the voltage across the device are both known, the value of that resistance can be determined from Ohm's law:

DUT

= VM/I

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Although the 4-wire measurement method minimizes the effects of lead resistances, other factors can affect low-resistance measurement accuracy. Thermal EMFs and other effects can add an extraneous dc offset voltage (V

OFFSET

) to the measured voltage. Refer to Minimizing thermal EMFs

(on page 5-4) for additional information.

Temperature-only connections

You can use Channel 1 of the 2182A to make temperature measurements. The following figure shows connections using the internal reference junction. The thermocouple wires must be soldered directly to the CHANNEL connector as described in Customized connections (on page 4-7).

Figure 17: Temperature connections (internal reference)

The following figure shows temperature-only connections using an ice bath as a simulated reference junction. The connection points for the input cable and the thermocouple wires are immersed in the ice bath.

Figure 18: Temperature connections (simulated reference)

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Voltage and temperature connections

Use Channel 1 for voltage measurements because it supports a wider range of measurements. Use Channel 2 to measure temperature.

A connection example using the internal reference junction for temperature measurements is shown in the following figure. In this example, Channel 1 measures the voltage drop across the DUT and Channel 2 measures the temperature of the DUT.

The jumper wire from the thermocouple to test circuit low is not needed in some test setups, such as:

• If the case of the DUT is metal and is connected to test circuit low.

• If there is enough thermal bonding between the DUT and test circuit low. In this setup, you can

connect the thermocouple directly to low.

Figure 19: Voltage and temperature connections (internal reference)

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The following figure shows the same test with a simulated reference junction (ice bath).

Figure 20: Voltage and temperature connections (simulated reference)

Cleaning test circuit connectors

Wherever possible, use copper-to-copper connections throughout your test circuits to minimize thermal EMFs. However, exposed copper is susceptible to oxidation, which can corrupt the measurement. Make sure that the copper contact surfaces are free of oxidation before making the connection. DeoxIT can be used to clean copper connectors. A small bottle of DeoxIT is supplied with the 2182A.

The Model 2107 Input Cable is terminated with copper lugs.

To clean the copper connectors used in your test circuit:

1. Using a lint-free foam swab (or other applicator), soak up a small amount of DeoxIT.

2. Apply the DeoxIT sparingly to the connectors. Only a thin coating is required.

After cleaning, make your test circuit connections in a timely manner to prevent oxidation from forming on exposed connector surfaces.

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Measuring voltage and temperature

Any time the internal temperature of the 2182A changes by 1 °C or more, the 10 mV and 100 V ranges need to be calibrated. Refer to ACAL (calibration) (on page 4-3) for details.

Whenever the connector of the Model 2107 Input Cable (or customized cable) is disconnected from the input of the 2182A for a long period, the input connectors must be cleaned to remove oxidation. Refer to Cleaning input connectors (on page 11-1) for details.

Do not use both channels to measure temperature. The electrical connection between the two thermocouples will cause erratic temperature readings.

Clean copper-to-copper connections minimize thermal EMFs. However, when measuring very low voltages, there may still be enough thermal EMFs to corrupt the measurement. In this case, use the relative offset feature of the 2182A to null out that offset. See Minimizing thermal EMFs (on page 5-4) for more information.

Temperature configuration

To make temperature measurements, you must configure the 2182A.

To configure temperature measurements using the front panel:

1. Press SHIFT and then TCOUP to open the temperature measurement menu.

2. Select UNITS to set the temperature units (°C, °F, or K).

3. Select SENS.

▪ To measure the internal temperature of the 2182A: Select INTERNL. ▪ To measure temperature at the thermocouple: Select TCOUPLE.

4. Select TYPE and select the thermocouple type that you are using to measure temperature (B, E,

J, K, N, R, S, or T).

5. Select JUNC and select the type of reference measurement:

▪ To reference measurements to the internal reference junction: Select INTRNL. ▪ To reference measurements to an external simulated reference: Select SIM. You are

prompted to enter the simulated reference temperature. Use the arrow keys to display the value and press ENTER.

The following basic measurement procedure assumes factory defaults. Reset the instrument to the factory default settings when following this step-by-step procedure. Refer to Default settings (on page 3-7) for detail on the defaults.

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To measure voltage and temperature:

1. Connect the test circuit to the input of the 2182A. Refer to Test connections (on page 4-5) for

details and drawings.

2. For temperature measurements, configure temperature settings as described in Temperature

configuration (on page 4-14).

3. Channel 1 is connected to measure voltage, so select DCV1.

4. Observe the reading on the display. The CH1 annunciator indicates that Channel 1 is selected.

Channel 2 inputs must be referenced to Channel 1 LO.

5. Channel 2 is connected to measure temperature, so select TEMP 2.

6. Observe the reading on the display. The CH2 annunciator indicates that Channel 2 is selected.

SCPI commands - voltage and temperature measurements

See the following SCPI command descriptions for descriptions and programming examples:

:SENSe[1]:FUNCtion (on page 13-55) :SENSe[1]:CHANnel (on page 13-53) :SENSe[1]:DATA:FRESh? (on page 13-54) :SENSe[1]:DATA[:LATest]? (on page 13-54) :SENSe[1]:TEMPerature:RJUNction:RSELect (on page 13-57) :SENSe[1]:TEMPerature:RJUNction:SIMulated (on page 13-58) :SENSe[1]:TEMPerature:TCouple[:TYPE] (on page 13-59) :SENSe[1]:TEMPerature:TRANsducer (on page 13-60) :UNIT:TEMPerature (on page 13-102)

Range

The voltage measurement range determines the full-scale value of the measurement range. The range also affects the accuracy of the measurements and the maximum voltage that can be measured.

You can allow the 2182A to choose the range automatically or you can select a specific range.

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The DCV1 function has five measurement ranges: 10 mV, 100 mV, 1 V, 10 V, and 100 V. The DCV2 function has three measurement ranges: 100 mV, 1 V, and 10 V. The range setting (fixed or automatic) is stored for each voltage function.

The available voltage ranges for ratio (V1/V2) depend on which channel is selected when ratio is enabled. If Channel 1 is selected, DCV1 ranges are available when ratio is enabled. If Channel 2 is selected, DCV2 ranges are available when ratio is enabled. Refer to Range settings when using ratio (on page 4-32) for complete information on ranging for ratio.

There is no range selection for temperature (TEMP 1 and TEMP 2) measurements. Temperature measurements are made on a single fixed range. You can change the reading resolution using the DIGITS key.

Maximum range readings

The full scale readings for every voltage range are 20% overrange. For example, on the 10 V range, the maximum input voltage is ±12 V.

The reading ranges for temperature depend on the type of thermocouple that is selected, as shown in the following table.

Thermocouple reading ranges

Type

Range

−200 °C to +760 °C

−200 °C to +1372 °C

−200 °C to +1300 °C

−200 °C to +400 °C

−200 °C to +1000 °C

0 °C to +1768 °C

+350 °C to +1820 °C

If an input value exceeds the maximum reading, the overflow message (OVRFLW) is displayed.

Manual ranging

To select a range, press the RANGE ▲ or ▼ key. The instrument changes one range for each key

press. The selected range is displayed for one second. The manual range keys have no effect on temperature readings. If the instrument displays OVRFLW when a range is selected, select a higher range until an on-range

reading is displayed. Use the lowest range possible without causing an overflow to ensure best accuracy and resolution.

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Autoranging

To enable autoranging, press the AUTO key. The AUTO annunciator turns on when autoranging is selected. While autoranging is enabled, the instrument automatically selects the best range to measure the applied signal. Each increase in range occurs at 120% of range. Each decrease occurs at 10% of nominal range.

If you require optimum speed, do not use autoranging. The AUTO key has no effect on temperature (TEMP 1 and TEMP 2).

To disable autoranging, press AUTO, then select the RANGE ▲ or ▼ key. If you press AUTO without

selecting another range, the instrument remains on the last range selected by autoranging.

SCPI programming - range

For information on the range SCPI commands, refer to:

• :SENSe[1]:VOLTage[:DC][:CHANnel<X>]:RANGe:AUTO (on page 13-65)

• :SENSe[1]:VOLTage[:DC][:CHANnel<X>]:RANGe[:UPPer] (on page 13-64)

Autozero modes

To ensure the accuracy of readings, the instrument must periodically get new measurements of its internal ground and voltage reference. The time interval between updates to these reference measurements is determined by the integration aperture. The 2182A uses separate reference and zero measurements for each aperture.

An A/D measurement cycle measures the input signal and periodically measures internal voltages that correspond to offsets (zero) and amplifier gains and the internal reference temperature. These measurements help maintain stability and accuracy over time and changes in temperature. The signal, offset, gain, and temperature measurements are then used in an algorithm to calculate the reading of the input signal. This process is called autozeroing.

Internally, the 2182A has two amplifiers that have an impact on speed, noise, drift, and offset. You can control these aspects to some degree by controlling the autozero modes. The front-end amplifier is controlled by Front Autozero, and the second amplifier is controlled by autozero.

Front Autozero

When Front Autozero is enabled, the 2182A performs two A/D measurement cycles for each reading. The first one is a normal measurement cycle, and the second one is performed with the polarity of the front-end amplifier reversed. This two-cycle, polarity-reversal measurement technique cancels internal offsets in the amplifier.

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When Front Autozero is disabled, the second A/D measurement cycle is not performed. Measurements are twice as fast and there is lower pumpout current noise. However, there is also high drift (20 µV/°C) and high offset voltage (±500 µV) in normal voltage mode.

To increase the speed of delta measurements, disable Front Autozero. The two-measurement cycle, polarity-reversal technique used by Front Autozero is not required for delta. Delta uses its own polarity-reversal technique to cancel offsets. Refer to Delta (on page 6-1) for more detail.

Autozero

When autozero for the second amplifier is disabled, the measurements for offset, gain, and internal reference temperature are not made. This increases measurement speed by a few percentage points at 1 power line cycle (PLC). However, disabling autozero can cause the zero, gain, and temperature reference points to drift, resulting in inaccurate readings for the input signal. It is recommended that autozero only be disabled for short periods.

When autozero is enabled after being off for a long time, the internal reference points are not updated immediately. This initially results in inaccurate measurements, especially if the ambient temperature has changed by several degrees. To force a single rapid update of the internal reference points when autozero is enabled, set the integration rate to FAST (or 0.01 PLC for remote programming), and then return it to the normal rate (such as MED; 1.0 PLC). For more information on integration rates, refer to

Rate (on page 4-19).

When autozero is disabled, pressing the front-panel RATE key changes the speed setting and enables autozero. If the rate is changed using remote programming, there is no change to the state of autozero.

To set the autozero mode from the front panel:

1. Press SHIFT and then CONFIG to display the present state of Front Autozero. Y is enabled; N is

disabled.

2. Press the ► key to display the present state of autozero: YES (enabled), NO (disabled).

3. To change the AUTOZERO setting, use the ▼ or ▲ key to display YES or NO.

4. Press ENTER to save the settings and exit from the menu structure.

To set the autozero mode using remote commands:

Refer to :SYSTem:AZERo[:STATe] (on page 13-80).

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Rate

The RATE key selects the integration time of the A/D converter. This is the time the input signal is measured and is also known as aperture. The integration time affects the amount of reading noise and the reading rate of the instrument. The integration time is specified in parameters based on the number of power line cycles (PLCs), where 1 PLC for 60 Hz is 16.67 ms (1/60) and 1 PLC for 50 Hz and 400 Hz is 20 ms (1/50).

The shortest amount of time, or lowest NPLC value, results in the fastest reading rate but increases the reading noise and decreases the number of usable digits.

The longest amount of time, or highest NPLC value, provides the lowest reading noise and more usable digits, but has the slowest reading rate.

The 2182A speed versus noise characteristics are shown in the following figure. The 2182A is optimized for the 1 PLC to 5 PLC reading rate. At these speeds, which are shown in the lowest noise region in the graph, the 2182A makes corrections for its own internal drift and is still fast enough to settle a step response of less than 100 ms.

Figure 21: Speed versus noise characteristics

You can have a separate rate setting for voltage and temperature functions. The rating that is set applies to both functions of that type (DCV1 and DCV2 or TEMP 1 and TEMP 2). For example, if you set DCV1 for 0.1 PLC, DCV2 is also set for 0.1 PLC.

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To set the rate from the front panel, select RATE and select one of the following options:

• 0.1 PLC: Selects the fastest front-panel integration time. Select 0.1 PLC if speed is most

important.

• 1 PLC: Selects a medium integration time. Select 1 PLC when a compromise between noise

performance and speed is acceptable.

• 5 PLC: Selects the slowest front-panel integration time. Selecting 5 PLC provides better noise

performance at the expense of speed.

Pressing the front-panel RATE key enables autozero if it was off. For remote programming, the rate commands have no effect on the state of autozero. For more information, see Autozeroing modes (on page 4-17).

To set the integration rate from the front panel:

1. Select the function.

2. Press the RATE key until the number of power line cycles (PLC) is displayed. The appropriate

annunciator turns on (FAST, MED, or SLOW).

SCPI programming - rate

For the SCPI commands that control the rate, refer to:

• :SENSe[1]:<function>:APERture (on page 13-42)

• :SENSe[1]:<function>:NPLCycles (on page 13-43)

If you are using remote commands, you can set the integration time from 0.01 PLC to 60 PLC (50 PLC for 50 Hz line power). You can also set integration time as an aperture time from 166.67 µs (200 µs for 50 Hz) to 1 second.

Filters

The 2182A has an analog filter and a digital filter. When the filter is enabled, the settings for the analog and digital filters are applied to the present measurement function (DCV1, DCV2, TEMP 1, or TEMP 2).

To enable the filter, press the FILT key. When the filter is enabled, the FILT annunciator is on. The filter state and configuration are saved for each measurement function.

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Analog filter

When you enable the low-pass analog filter, the normal-mode noise rejection ratio of the instrument is increased at 60 Hz. This filters out noise induced by the power line. The analog filter attenuates frequency at 20 dB/decade starting at 18 Hz.

A primary use of the analog filter is to keep the high-gain input stage of the 2182A from saturating due to the presence of high ac and dc voltage.

The filter only attenuates ac voltages for the 10 mV range of the 2182A.

The analog filter adds approximately 125 ms of settling time between A/D conversions. The additional settling time may be required when using a high-impedance (≥100 kΩ) source in the test circuit. The increased settling time causes the reading rate of the 2182A to be greatly reduced. Therefore, if the analog filter is not needed, turn it off.

Digital filter

The digital filter stabilizes noisy measurements. The displayed, stored, or transmitted reading is a windowed-average of a number of reading conversions (from 1 to 100).

In general, the digital filter places a specified number of consecutive A/D conversions (filter count) into a memory stack. The readings in the stack are then averaged to yield a single filtered reading. You can set the filter to use a moving or repeating average.

When the moving average filter is selected, the measurements are added to the stack continuously on a first-in, first-out basis. As each measurement is made, the oldest measurement is removed from the stack. A new averaged sample is produced using the new measurement and the data that is now in the stack.

When the moving average filter is first selected, the stack is empty. When the first measurement is made, it is copied into all the stack locations to fill the stack. A true average is not produced until the stack is filled with new measurements. See the following figure for an example of a moving average filter.

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Figure 22: Moving average filter

When the repeating average filter is selected, a set of measurements are made. These measurements are stored in a measurement stack and averaged together to produce the averaged sample. Once the averaged sample is produced, the stack is flushed, and the next set of data is used to produce the next averaged sample. This type of filter is the slowest, since the stack must be completely filled before an averaged sample can be produced, but it provides more stable results. See the following figure for an example of a repeating average filter.

Figure 23: Repeating average filter

For either method, the greater the number of measurements that are averaged, the slower the averaged sample rate, but the lower the noise error. Trade-offs between speed and noise are normally required to tailor the instrumentation to your measurement application.

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Digital filter characteristics

You can set the filter type, filter count, and filter window for the digital filter. You can set the filter type to moving or repeating, as described in Digital filter (on page 4-21). If you are using delta measurements, you must use the moving filter. When delta measurements are

selected, if filters are enabled, the 2182A uses a moving filter regardless of the filter type setting. Refer to Delta (on page 6-1) for more information on delta measurements.

If you are stepping or scanning, you must use the repeating filter. When the instrument is stepping or scanning and filters are enabled, the 2182A uses a repeating filter regardless of the filter type setting. Refer to Stepping and scanning (on page 7-1) for more information.

The filter count specifies how many consecutive A/D conversions in the filter window to place in the memory stack. When the stack is full, the A/D conversions are averaged to calculate the final filtered reading. The filter count can be set from 1 to 100. If the filter count is 1, no averaging is done. Only readings in the filter window are displayed, stored, or transmitted.

The digital filter uses a window to control the filter threshold. While the input signal remains in the selected window, A/D conversions continue to be placed in the stack. If the signal changes to a value outside the window, the filter resets, and the filter starts processing again, starting with a new initial conversion value from the A/D converter.

From the front panel, you can select a window of 0.01%, 0.1%, 1%, or 10% of range, or NONE (no window). With remote commands, you can set the window to any value from 0% to 10% or NONE.

For the voltage function, the filter window is expressed as a percent of range. For example, on the 10 V range, a 10% window means that the filter window is ±1 V. For temperature, the filter window is expressed as a percent of the maximum temperature reading. The maximum temperature depends on which thermocouple is used. For example, for a Type J thermocouple, the maximum reading is 760 °C, so a 10% window creates a filter window of ±76 °C.

Filter control and configuration

The FILT key toggles the state of filters. When filter is enabled, the FILT annunciator is on. You can configure the analog and digital filters while filter is enabled or disabled. If filter is enabled, changes to the configuration take effect as soon as they are made. With filter disabled (FILT annunciator off), changes to the configuration take effect the next time the filter is enabled.

If both the analog and digital filters are configured to be off and filter is enabled, the digital filter automatically turns on. This ensures that some type of filtering is applied when the FILT annunciator is on.

While the filtering operation is in progress, the FILT annunciator blinks. Readings continue to be processed, but they may be questionable. When the FILT annunciator stops blinking, the filter has settled.

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Filters are reset when the function or range changes. The filter settings change to the state (enabled or disabled) and configuration for that function or range.

When both channels are being measured for ratio, the filter state (enabled or disabled) and configuration for DCV1 is used.

To configure the filter using the front panel:

1. Select the function (DCV1, DCV2, TEMP 1, or TEMP 2).

2. Press SHIFT and then TYPE. The present state of the analog filter is displayed.

3. To enable or disable the analog filter, use the ◄ and ► keys to move the cursor to ON or OFF.

Press the RANGE ▲ or ▼ key to change the setting.

4. Press ENTER. The present state of the digital filter (on or off) is displayed.

5. To change the state of the digital filter, use the ◄ and ► keys to move the cursor to ON or OFF.

Press the RANGE ▲ or ▼ key to change the setting.

6. Press ENTER. The present digital filter window setting is displayed.

7. Use the RANGE ▲ or ▼ key to display the window setting.

8. Press ENTER. The present digital filter count is displayed.

9. To change the count, use the ◄ and ► keys and ▲ and ▼ keys to display the count setting.

10. Press ENTER. The present digital filter type is displayed.

11. To change the digital filter type, place the cursor on the type name and press the RANGE

▲ or ▼ key.

12. Press ENTER. The instrument returns to the normal measurement display state.

Digital filter example

Filter Count = 10 Filter Window = 0.01% of range Filter Type = Moving

Ten readings fill the stack to yield a filtered reading. Now assume the next reading (which is the 11th) is outside the window. A reading is processed and displayed; however, the stack is loaded with that same reading. Each subsequent valid reading then displaces one of the loaded readings in the stack. The FILT annunciator flashes until 10 new readings fill the stack.

Bit 8 of the Operation Event Status Register sets when the filter window has settled. See Status

structure (on page 16-1) for details.

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SCPI programming - filter

See the following SCPI command descriptions for descriptions and programming examples:

:SENSe[1]:<function>[:CHANnel<X>]:DFILter:COUNt (on page 13-45) :SENSe[1]:<function>[:CHANnel<X>]:DFILter:TCONtrol (on page 13-46) :SENSe[1]:<function>[:CHANnel<X>]:DFILter:WINDow (on page 13-47) :SENSe[1]:<function>[:CHANnel<X>]:DFILter[:STATe] (on page 13-48)

Relative offset

When making measurements, you may need to subtract an offset value from a measurement. The relative offset feature subtracts a set value or a baseline reading from measurement readings.

When you enable relative offset, all measurements are recorded as the difference between the actual measured value and the relative offset value. The formula to calculate the offset value is:

Displayed value = Actual measured value − Relative offset value

When a relative offset value is established for a measure function, the value is the same for all ranges for that measure function. For example, if 5 V is set as the relative value on the 10 V range for DCV1, the relative value is also 5 V on the 100 V, 1 V, 100 mV, and 10 mV ranges.

On the front panel, when relative offset is enabled, the REL indicator is displayed. When a relative value is larger than the selected range, the display is formatted to accommodate the

reading with the offset applied. However, this does not increase the maximum allowable input for that range. An overrange input signal still causes the display to overflow. For example, on the 10 V range, the 2182A overflows for a 12 V input.

For information on using readings with offset applied in ratio calculations. See Ratio (on page 4-31) for more information.

For information on canceling residual thermal offsets, see Canceling residual thermal offsets (on page 5-4).

For information on setting a relative offset value for the analog output, see Analog output (on page 4-34).

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For offsets that vary, use the dc current-reversal technique instead of relative offset. This technique uses the delta measurement mode of the 2182A to cancel offsets. Refer to Delta, pulse delta, and

differential conductance (on page 6-1) for more information.

You can use the mx+b function to manually establish a relative offset value. To do this, set the scale factor (m) to 1 and set the offset (b) to the offset value. Each subsequent reading is the difference between the actual input and the offset value.

The relative offset value is set for the selected function (DCV1, DCV2, TEMP 1, or TEMP 2). You can set a unique relative offset value for each measurement function and for each channel.

To set a relative offset value from the front panel:

1. Connect the test circuit.

2. Turn on the instrument and leave the source (voltage or current) disconnected or in stand-by.

3. Select the channel.

4. Select the function.

5. Display the reading you want to use for the relative offset value, such as a zero offset reading that

you want to null out or an applied level that you want to use as a baseline.

6. If you are not using autorange, select the lowest possible measurement range to display the

voltage offset.

7. Press the REL key to zero the display. The REL annunciator turns on and subsequent readings

are the difference between the actual input and the relative offset value.

8. To disable the relative offset, press the REL key again. The REL annunciator turns off.

SCPI programming - relative offset

For information on setting relative offset using SCPI commands, refer to:

:SENSe:<function>[:CHANnel<X>]:REFerence (on page 13-50) :SENSe:<function>[:CHANnel<X>]:REFerence:ACQuire (on page 13-51) :SENSe:<function>[:CHANnel<X>]:REFerence:STATe (on page 13-52)

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Pumpout current (low charge injection mode)

Pumpout current is a small discharge of current at the meter input. Pumpout current can sometimes be a problem for low-level signals. A symptom of a pumpout current problem is when there appears to be noise injections in the measurement results. This current discharge results from the switching the instrument does between measurements of the input signal and the background measurements made by the analog to digital (A/D) converters, which include measurement of reference and zero points.

Pumpout current for Channel 1 is very low (0.5 µA peak-to-peak) and therefore does not adversely affect instrument performance. The pumpout current for Channel 2 is also very low if Channel 2 LO is connected to Channel 1 LO.

Settling for the transition occurs on the next A/D conversion. Whenever the impedance between Channel 2 LO and Channel 1 LO is >100 kΩ, pumpout current could be high enough to corrupt measurements below 1 V. Above 1 V measurements, pumpout current is not significant.

If you must use Channel 2 for measurements below 1 V and the impedance between Channel 2 LO and Channel 1 LO is >100 kΩ, you can enable the low charge injection mode to reduce the pumpout current. However, this mode increases measurement noise by up to eight times.

Low charge injection mode is only available through a remote interface. To enable low charge injection mode, send the command:

CALL SEND(7,":SENS:VOLT:CHAN2:LQM ON",status%)

Refer to :SENSe[1]:VOLTage[:DC]:CHANnel2:LQMode (on page 13-61) for more information on low charge injection mode.

Line cycle synchronization

Using line synchronization helps increase common-mode and normal-mode noise rejection. When line cycle synchronization is enabled, measurements are initiated at the first positive-going zero crossing of the power line cycle after the trigger.

The following figure shows the measurement process, which consists of two A/D conversions. If the trigger occurs during the positive cycle of the power line (as shown in the figure), the first A/D conversion starts with the negative-going zero crossing of the power line cycle. If the next trigger (Trigger #2) occurs during the negative cycle, the measurement process starts with the positive-going zero crossing.

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Figure 24: Line cycle synchronization

Line cycle synchronization is not available for integration rates <1 PLC, regardless of the LSYNC setting.

To enable or disable line cycle synchronization from the front panel:

1. Press SHIFT and then LSYNC to display the present state of line synchronization (OFF or ON).

2. Use ▼ or ▲ key to display ON or OFF.

3. Press ENTER. The instrument returns to the normal display state.

SCPI programming - Line cycle synchronization

Refer to :SYSTem:LSYNc[:STATe] (on page 13-86).

Calculations that you can apply to measurements

The 2182A allows you to apply the following math operations to the measurement:

• mx+b

• percent

The calculations are applied to all measurement functions.

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mx+b

The mx+b math operation lets you manipulate normal display readings (x) mathematically based on the following calculation:

mx + b = y Where:

• m is a user-defined constant for the scale factor

• x is the measurement reading (if you are using a relative offset, this is the measurement with

relative offset applied)

• b is a user-defined constant for the offset factor

• y is the displayed result

The mx+b function does not affect the analog output. Analog output has its own gain and offset settings. Refer to Analog output (on page 4-34) for more information.

To configure the mx+b calculation from the front panel:

1. Press the SHIFT key and the MX+B key to display the present scale factor. The default is 1.

2. Enter the m factor. Use ◄ and ► to move the cursor and ▲ and ▼ to increase or decrease the

value.

3. To change the range, place the cursor on the multiplier and use the ▲ and ▼ keys to display the

range (m = ×0.001, ^ = ×1, K = ×1000, and M = ×1,000,000). With the cursor on the polarity sign, the ▲ and ▼ keys toggle polarity.

4. Press ENTER to enter the m value and display the b value:

B: +00.000000 m (factory default)

5. Enter the offset value.

6. Press ENTER to enter the b value and display the two-character UNITS designator:

UNITS: MX (factory default)

7. Use the cursor keys and the ▲ and ▼ key to change the units designator. Each character can be

any letter in the alphabet (A through Z), the degrees symbol (°), or the ohms symbol (Ω).

8. Press ENTER. The MATH annunciator turns on, and the result of the calculation is displayed.

9. To disable mx+b, press SHIFT and then MX+B. The MATH annunciator turns off.

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Percent (%)

The percent math function determines the percent deviation from a specified reference value. The percent calculation is made as follows.

Where:

• Percent is the displayed result

• Input is the normal display reading

• Reference is the user-entered constant

The result of the percent calculation is positive when the input exceeds the reference and negative when the input is less than the reference. The result of the percent calculation may be displayed in exponential notation. For example, a displayed reading of + 2.500E+03% is equivalent to 2500%.

To configure and control the percent calculation:

1. Press SHIFT and then % to display the present reference value.

REF: +1.000000 ^ (factory default)

2. To change the range, place the cursor on the multiplier and use the ▲ and ▼ keys (m = ×0.001,

^ = ×1, K = ×1000, and M = ×1,000,000). With the cursor on the polarity sign, the ▲ and ▼ keys toggle polarity.

3. Enter a reference value. The ◄ and ► keys control cursor position and the ▲ and ▼ range keys

increment and decrement the digit value.

4. Press ENTER. The MATH annunciator turns on and the result of the calculation is displayed.

5. To disable percent, press SHIFT and then %. The MATH annunciator turns off.

SCPI programming - mx+b and percent

Refer to CALCulate[1] subsystem (on page 13-6) for detail on programming mx+b and percent.

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Ratio

Ratio (V1/V2) displays the proportional relationship between the two voltage input channels (DCV1 and DCV2). Ratio is calculated as follows:

Ratio = V1/V2 Where:

• V1 is the voltage reading for Channel 1 (DCV1)

• V2 is the voltage reading for Channel 2 (DCV2)

When the ratio feature is selected, one of the channel annunciators (CH1 or CH2) turns on briefly. This indicates the channel that you can control with the manual range key. After the brief display, the CH1 and CH2 annunciators are active. You can press the AUTO range key to either enable autorange for both channels or disable autorange for both channels. Refer to Range settings when

using ratio (on page 4-32) for additional information.

Line cycle integration (LSYNC) must be enabled when ratio is selected. LSYNC turns on automatically when ratio is enabled and turns off automatically when ratio is disabled.

If an overflow condition (OVRFLW) occurs, the range that overflowed formats the display. Ratio readings can be stored in the buffer.

You cannot use reading hold with ratio. Selecting ratio disables reading hold.

A hazardous voltage condition exists at or above 42 V

PEAK

. To prevent electric shock that could result in injury or death, never make or break connections while hazardous voltage is present.

Channel 1 HI and LO terminals have a maximum measurement capability of 120 V

PEAK

. These

inputs are protected to 150 V

PEAK

to any terminal or 350 V

PEAK

to chassis. Exceeding these

limits may cause instrument damage not covered by the warranty.

Channel 2 HI and LO terminals have a maximum measurement capability of 12 V

PEAK

Channel 1 LO. Channel 2 HI is protected to 150 V

PEAK

to any terminal. Channel 2 LO is

protected to 70 V

PEAK

to Channel 1 LO. Both inputs are protected to 350 V

PEAK

to chassis.

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To set ratio from the front panel:

1. Connect the 2182A for voltage as described in Test connections (on page 4-5).

2. Configure each channel (DCV1 and DCV2) for the voltage measurement.

3. Verify that DCV1 and DCV2 are displaying on-scale readings. If an OVRFLW message is displayed

for any channel, select a higher range until an on-scale reading is displayed. You can also press AUTO to enable the autorange feature.

4. If you want the manual range keys to control Channel 1 ranges, press DCV1. If you want the

manual range keys to control Channel 2 ranges, select DCV2.

5. To enable ratio, press the V1/V2 key. While in ratio, the RA message is displayed.

6. Make ratio readings from the display.

7. To disable ratio, select a single measurement function (DCV1, DCV2, TEMP 1, or TEMP 2)

or Delta.

SCPI command - ratio

Refer to :SENSe:VOLTage[:DC]:RATio (on page 13-63) for the command description.

Range settings when using ratio

You can use a separate range setting (fixed or automatic) for each voltage channel. When ratio is enabled, the range setting for each channel is retained. For example, you can set Channel 1 to autorange and you can set Channel 2 to the 10 V range.

The manual range keys can only control one of the two channels. If the instrument is on DCV1, TEMP 1, or TEMP 2 when ratio is enabled, the manual range keys control Channel 1 (DCV1). If the instrument is on DCV2 (Channel 2) when ratio is enabled, range control applies to Channel 2 (DCV2). When a range key is pressed, the channel number annunciator for the range-controlled channel remains on. The other channel annunciator turns off for a moment.

The state (on or off) of the AUTO range annunciator indicates the state of autorange for the voltage channel that is under range control. When ratio is enabled, pressing the AUTO range key either disables autorange for both channels or enables autorange for both channels (AUTO annunciator turns on).

When ratio is enabled, the range control channel is displayed while the CH1 / CH2 message is displayed.

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Relative offset when using ratio

You can set a separate relative offset value for each voltage channel. When ratio is enabled, the relative offset values are applied to the respective channels before the calculation is made.

Ratio with relative off set applied is calculated as follows: Ratio = (Filt V1 − V1 Rel) / (Filt V2 − V2 Rel) Where:

• Filt V1 is the filtered reading for Channel 1 voltage input

• V1 Rel is the relative offset value established for Channel 1

• Filt V2 is the filtered reading for Channel 2 voltage input

• V2 Rel is the relative offset value established for Channel 2

The previous calculation shows Filter enabled. If Filter is not used, remove the "Filt" component from the calculation.

When ratio is enabled, the state (on or off) of the REL annunciator depends on which measurement function was last selected. If the function is DCV1 when ratio is enabled, the REL annunciator indicates the state for DCV1. If the function is DCV2 when ratio is enabled, the REL annunciator indicates the state of relative offset for DCV2.

The REL key is operational while in ratio. When you press REL, it either disables relative offset for both channels or enables relative offset for both channels. When relative offset is enabled, the instrument acquires the input signal from each of the two channels as relative offset values. Each relative offset value is then applied to the respective channel.

Relative offset operations are performed on the input channels, not on the result of ratio.

For more information on relative offset, see Relative offset (on page 4-25).

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Analog output

The analog output is a scaled, non-inverting voltage output up to ±1.2 V. It is typically used to drive a chart recorder. The analog output voltage is calculated as follows:

Analog output = (Gain × Reading/Range) − Offset Where:

• Gain is the user-entered gain factor

• Reading is the reading on the 2182A

• Range is the measurement range

• Offset is a user-entered offset value

Gain and offset for the analog output are not related to gain and offset for the mx+b calculation.

Gain provides amplification for small analog output voltage signals, while offset allows you to adjust the analog output to keep it between the maximum output of ±1.2 V or reference the voltage output to a specific value, such as zero.

For example, assume you are measuring 100 mV on the 1 V range. With gain set to 1, the analog output is 100 mV. You can increase analog output sensitivity by setting the gain to 10. This increases the analog output to 1 V. You can then set the offset to 1 V to reference the 1 V analog output to zero. The analog output calculation for this example is:

Analog output = (10 × 100 mV/1 V) − 1 V = 0 V The factory default for gain is 1 and the factory default for offset is 0. Therefore, when using the

factory defaults, gain and offset drop out of the equation: Analog Output = Reading/Range The following table shows analog output examples with the gain set to 1 and offset set to 0.

Reading

Range

Analog output voltage

1 V

+1 V

−1 V

1 V

−1 V

1 V

10 V

0.1 V

12 V

10 V

1.2 V

50 mV

100 mV

0.5 V

−1 mV

1 V

−1 mV

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Temperature

The analog output voltage for temperature measurements depends on thermocouple type and the selected units (°C, °F, or K). The 1.2 V analog output is scaled to the maximum positive temperature reading. For example, the measurement range for the type J thermocouple is −200°C to +760°C. For a 760°C reading, the analog output voltage is 1.2 V. For a −200°C reading, the analog output voltage is −0.316 V. The measurement ranges (in °C) for the various thermocouple types are listed in the specifications, available at tek.com/keithley.

With the gain set to 1 and offset set to 0, analog output voltage for temperature measurements is calculated as follows:

Analog output = 1.2 × Reading/Range In this formula, range is a magnitude, so it is always a positive value. Example calculations:

Type J, 100°C reading

Type J, –100°C reading

Analog output

= 1.2 × 100/760

Analog output

= 1.2 × (−100/760)

= 158 mV

= −158 mV

When using gain and offset, the calculation is expanded as follows: Analog output = (Gain × 1.2 × Reading/Range) – Offset

Ratio

You can use analog output with the ratio feature. When enabled, the analog output voltage is scaled to a ratio value of 1. That is, the analog output is 1 V for a ratio result of 1. If, for example, the ratio is

0.4, the analog output voltage is 0.4 V. You can also use gain, offset, and analog output relative offset.

The maximum analog output is ±1.2 V. Refer to Ratio (on page 4-31) for more information on using the ratio feature.

Analog output connections

The analog output is accessed from the rear-panel BNC connector labeled ANALOG OUTPUT. This connector requires a cable that is terminated with a standard male BNC connector.

The output resistance of the analog output is 1 kΩ ±5%. To minimize the effects of loading, the input resistance of the device connected to ANALOG OUTPUT should be as high as possible. For example, for a device with an input resistance of 10 MΩ, the error due to loading is approximately 0.01%.

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Configure the analog output

To configure the analog output:

1. Press SHIFT and then AOUT to display the Gain (M) factor. The default is 1, with a range of

−100e6 to 100e6.

2. Use the ◄ and ► keys to move the cursor position and the ▲ and ▼ range keys to increment

and decrement the digit value. To change the range, place the cursor on the multiplier and use

the ▲ and ▼ keys (m = ×0.001, ^ = ×1, K = ×1000, and M = ×1,000,000). With the cursor on the polarity sign, the ▲ and ▼ keys toggle polarity.

3. Press ENTER to enter the gain value and display the Offset value B. The default is 0.

4. Enter the offset value.

5. Press ENTER to enter the offset value and enable the analog output. The instrument returns to

the normal display state.

6. To disable the analog output, press SHIFT and then AOUT.

Analog output relative offset

When analog output is enabled, the analog output relative offset automatically references the analog output voltage to zero.

If you enable relative offset when the analog output is enabled, the present analog output voltage is used as the relative offset value. This sets the analog output voltage to zero. Subsequent analog output readings are the difference between the actual analog output and the relative offset value.

To enable the analog output relative offset from the front panel, press SHIFT and then OUTPUT. The message AOUT REL ON is displayed briefly. To disable the analog output relative offset, press SHIFT and then OUTPUT again. The message AOUT REL OFF is displayed briefly.

You can establish a new relative offset value for the analog output by disabling the analog output relative offset and enabling it again.

SCPI programming - analog output

Commands and programming examples for analog output are described in OUTPut subsystem (on page 13-36).

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Applications

The following examples demonstrate common 2182A applications.

Heated Zener reference and Josephson Junction Array

comparisons

You can analyze the performance of a heated Zener reference by comparing it to a Josephson Junction (JJ) Array using both channels of the 2182A. In a cryogenic environment, the JJ Array provides an output voltage in precise, stable 175 µV steps.

The test circuit for this application is shown in the following figure. The JJ Array is adjusted until Channel 1 of the 2182A measures 0 V ±10 µV. The null condition indicates that the heated Zener reference voltage is the same as the JJ Array voltage. Channel 2 of the 2182A determines the exact step that the JJ Array is on. You can then monitor Channel 1 to study noise and drift characteristics of the heated Zener reference.

Figure 25: Heated Zener characterization

Calibrating resistor network dividers

You can use the ratio feature to calibrate resistor network dividers. The 1:10 divider network in the following figure is made up of nominal resistances of 1 kΩ and 10 kΩ. The 1 kΩ resistance is the result of the parallel combination of the 2 kΩ pot and the 2 kΩ resistor. The pot provides fine-tuning of the network.

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Figure 26: Calibrating 1:10 divider

Use the Keithley Model 6220 to source a constant current of 1 mA. Channel 1 is set to the 1 V range (1 kΩ × 1 mA = 1 V) or autorange. Channel 1 measures the 1 kΩ resistance component of the network. Channel 2 is set to the 10 V range or autorange. Channel 2 measures the 10 kΩ resistance component.

When ratio is enabled, the 2182A displays the result of V1 (approximately 1 V) divided by V2 (approximately 10 V):

Ratio =

FiltV1

≈1 V

= ≈0.1

FiltV2

≈10 V

This calculation includes the Channel 1 Filter. If a filter is not used, remove the Filt component from the calculation.

The network can then be calibrated by adjusting the network pot until a reading of 0.10000 is displayed.

For even greater precision, you can use the relative offset feature of the 2182A to cancel thermal EMFs, which can corrupt low voltage measurements.

To use relative offset with ratio:

1. While displaying the ratio result, disconnect the current source from the network.

2. Press the REL key on the 2182A. The voltages at each input, which are thermal EMFs, are

cancelled.

3. Reconnect the current source and take the result of ratio from the display. When using relative offset, the ratio is calculated as follows:

Ratio =

Filt V1 − V1 Rel

Filt V2 − V2 Rel

This calculation includes the Channel 1 Filter. If a filter is not used, remove the Filt component from the calculation.

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Testing superconductor materials

A superconductor sample is typically tested by either varying the current through it or varying the magnetic field that surrounds it.

The following applications use magnetic field (H) as one of the test parameters. You can modify the applications to substitute temperature (T) for H as a test parameter.

When varying the magnetic field, the current (I) that flows through the DUT is fixed. When varying the current through the superconductor material (DUT), the magnetic field that surrounds it is held constant.

For the following applications, the 2182A measures voltage and a Keithley SourceMeter Model 2400, 2410, or 2420 sources a known current. The actual resistance of the DUT can be calculated using Ohm’s Law.

Test leads that connect the 2182A to the superconductor sample (DUT) in a cryostat are typically 30 feet or longer. The test lead connections and the wide temperature range (from ~0 K at the DUT to the ambient temperature of the lab) create substantial thermal EMFs in the test leads. The effects of these thermal EMFs must be canceled to achieve accurate voltage measurements.

Superconductor Application 1: Fixed current

A typical test on a superconductor sample (DUT) is to vary the magnetic field (H) while maintaining a fixed current (I) through the DUT, as shown in the following figure. The current source of the SourceMeter is a constant current source. Therefore, the current through the DUT remains constant as the resistance of the DUT increases.

Figure 27: Test fixture with fixed current (Vary H)

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After measuring the DUT voltage (V) at a series of increasing magnetic field values, you can graph H versus V. The example H-V curve in the following figure shows that the measured voltage across the DUT remains at ~0 V in low magnetic fields. This is the flat portion of the curve where the DUT remains at 0 Ω. At some point, the voltage drop across the DUT starts to increase as the magnetic field increases. The actual resistance of the DUT can be calculated at any magnetic field point using Ohm’s law:

R = V/I where:

• R is actual resistance of the DUT.

• V is the measured voltage across the DUT.

• I is the known current that flows through the DUT.

Figure 28: H-V curve (fixed current)

To cancel the effects of thermal EMFs in the test leads, you must use the dc current reversal measurement technique. By configuring a custom sweep, the SourceMeter can function as a fixed bipolar amplitude source. For example, if the test requires a fixed current of 1 mA, the custom sweep can be configured to alternate between +1 mA and −1 mA, as shown in the following figure. By enabling delta measurements on the 2182A, the effects of thermal EMFs in the test leads are automatically canceled during the source-measure process.

Figure 29: SourceMeter output: Two-point custom sweep

The procedure to use the SourceMeter and 2182A to perform delta measurements is provided in

Delta measurement procedure using a SourceMeter (on page 6-5). That procedure uses a 2-point

custom sweep, which is required for this application.

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Superconductor Application 2: Fixed magnetic field

Another typical test on a superconductor sample (DUT) is to source an increasing-amplitude current (I) through the DUT, while maintaining the magnetic field (H) at a fixed level. The I-V curve in the following figure shows that the measured voltage across the DUT remains at ~0V for low currents. This is the flat portion of the curve where the DUT remains at 0 Ω. At some point, the voltage drop across the DUT starts increasing as current through the DUT increases. The actual resistance of the DUT can be calculated at any current source point using Ohm’s law:

R = V/I where:

• R is actual resistance of the DUT.

• V is the measured voltage across the DUT.

• I is the known current that flows through the DUT.

Figure 30: Current-voltage curve (fixed H)

An example of this test system is shown in the following figure. A Keithley SourceMeter (Model 2400, 2410, or 2420) sources current through the DUT and two 2182As provide simultaneous voltage measurements.

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Figure 31: Test circuit: Fixed H (Vary I)

2182A 1 measures the voltage across a precision reference resistor (R

REF

) and stores the readings in its buffer. These stored readings allow you to reference current amplitudes to the voltage measurements of the DUT. 2182A 2 measures voltage across the DUT and stores the readings in its buffer.

For example, assume you want to measure DUT voltage at current sweep values of 10 µA, 20 µA, and 50 µA. When the sweep is started (10 µA output), 2182A 1 measures 1 mV (10 µA × 100 Ω = 1 mV) and stores the reading in its buffer at location 1. At the same time, 2182A 2 measures the DUT and stores that reading in its buffer at location 1. At the next sweep point (20 µA), 2182A 1 measures 2 mV and stores the reading in its buffer at location 2, and 2182A 2 measures the DUT and stores the reading in its buffer at location 2. At the last sweep point (50 µA), 2182A 1 measures 5 mV and stores the reading in its buffer at location 3, and 2182A 2 measures the DUT and stores the reading in its buffer at location 3.

The readings in the buffer of 2182A 1 correspond to the current sweep values. You can use the buffer location numbers to reference DUT readings to current amplitudes, shown in the following table.

2182A 1 buffer

2182A 2 buffer

RDG NO. 1 = 1 mV: 10 µA

RDG NO. 1 = DUT measurement

RDG NO. 2 = 2 mV: 20 µA

RDG NO. 2 = DUT measurement

RDG NO. 3 = 5 mV: 50 µA

RDG NO. 3 = DUT measurement

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To cancel the effects of thermal EMFs in the test leads, the dc current reversal measurement technique must be used. By configuring a custom sweep, the SourceMeter can function as a bipolar growing amplitude source.

For example, if the test requires current steps of 10 µA, 20 µA, and 50 µA, the 6-point custom sweep would be configured as follows:

P0000 = +10 µA

P0001 = −10 µA

P0002 = +20 µA

P0003 = −20 µA

P0004 = +50 µA

P0005 = −50 µA

By enabling delta measurements on the 2182A, the effects of thermal EMFs in the test leads are automatically canceled during the source-measure process.

To check measurement repeatability, you can make more than one delta measurement at each current amplitude. In the following figure, the SourceMeter outputs five bipolar steps for each amplitude. The result is five delta measurements for each amplitude. When configuring the custom sweep, ±10 µA is assigned to the first 10 points of the sweep, ±20 µA is assigned to the next 10 points, and ±50 µA is assigned to the last 10 points. Therefore, the custom sweep is made up of 30 points (P0 through P29).

Figure 32: SourceMeter output: 30-point custom sweep

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The procedure to use a SourceMeter and 2182A to make delta measurements is provided in Delta

measurement procedure using a SourceMeter (on page 6-5). That procedure uses a 2-point custom

sweep and must be modified for this application as follows:

• This application uses two 2182As that must be configured exactly the same.

• Change the trigger count to equal the number of points in the custom sweep. For example, if

using the 30-point custom sweep, set the trigger count to 30.

• Assign current values to the sweep points. For the example 30-point sweep, the current values

for points P0 through P29 are shown in the figure above.

• Set the buffers of both 2182As to store the delta readings. If performing a 30-point sweep, set

both buffers to store 30 delta readings.

• Enable line synchronization on both 2182As. To access control, press SHIFT and then LSYNC.

Optimum synchronization among all instruments is achieved when 2182A line synchronization is enabled and autozero is disabled. Autozero cannot be disabled from the front panel of the 2182A. When controlling this application over the bus, use the following commands for the 2182As:

:SYSTem:LSYNc:STATe ON 'Enable 2182A Line Synchronization :SYSTem:AZERo:STATe OFF 'Disable 2182A Autozero

Autozero should only be disabled for short periods. After performing a sweep, re-enable Autozero. Refer to Autozero modes (on page 4-17) for details.

If your test requires currents that span two or more decades, you can configure the SourceMeter to output a log sweep. The 30-point sweep in the figure above is confined to the 10 µA to 100 µA decade. If you want to expand the sweep to span three current decades, use the next 30 sweep points for the 100 µA, 200 µA, and 500 µA amplitudes. The last 30 sweep points are used for the 1 mA, 2 mA, and 5 mA amplitudes. The I-V data points can then be graphed using a logarithmic/linear scale.

External triggering synchronizes source-measure operations among the instruments. The SourceMeter must trigger both 2182As to achieve simultaneous measurements. In turn, only one of the 2182As must trigger the SourceMeter to output the next source value.

The trigger link connections required for this application are shown in the following figure. The output trigger (VMC) is provided by 2182A 1. Do not use VMC from 2182A 2.

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Figure 33: Trigger Link connections using two 2182A instruments

Low-resistance measurements

You can use the 2182A with a current source to measure resistances at levels below the capabilities of most conventional instruments. The following paragraphs discuss low-resistance measurement techniques and include some applications to test switches.

Low power switches

The following figure shows how to use the 2182A to measure the resistance of a switch contact. The constant current is provided by the current source, which can source up to 100 mA. To avoid oxide puncture, the voltage across the switch contact should be ≤20 mV. Voltage is limited by choosing a current that will not result in a voltage drop that is larger than 20 mV. For example, with a contact resistance specified at 500 mΩ, the current should be no larger than 40 mA.

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Figure 34: Measuring switch contact resistance

With current known and voltage measured, you can calculate resistance using Ohm's Law:

R = V/I

High power switches

Heat is a factor in high power switching. As the temperature of the switch increases, so does the contact resistance. In the following figure, heat is generated in the switch by sourcing a constant high current, such as 10 A, through it.

Figure 35: Measuring switch contact resistance and temperature

The 2182A measures both the voltage across the switch contact and the temperature. These measurements allow you to develop a resistance versus temperature profile. With current known and voltage measured, you can calculate resistance using Ohm's Law:

R = V/I

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Standard cell comparisons

Standard cell comparisons are conducted by measuring the potential difference between a reference and an unknown standard cell. All cell differences are determined in series opposition configuration. The positive terminals of the standard cells (V1 and V2) are connected to the HI and LO inputs of the nanovoltmeter, as shown in the following figure. Use the Model 2107 Input Cable to connect the cells to the nanovoltmeter to minimize errors caused by thermal EMFs (V

EMF

Figure 36: Standard cell comparison measurements - Reading 1

Once the measurement connections are made, care must be taken to avoid errors from thermally generated potentials. To minimize the effects of thermal EMFs, a second measurement is made with the nanovoltmeter leads reversed, as shown in the following figure. The small voltage difference is calculated by averaging the absolute values of the two readings. Calculation of standard deviation across several redundant readings helps provide this assurance.

Figure 37: Standard cell comparison measurements - Reading 2

Once stability is achieved, the actual voltage difference between the cells is measured. For each comparison, several readings are usually averaged. This process of comparing is then repeated each week, month, or year, depending upon the standards laboratory. The results can then be plotted and compared over time.

In this section:

Introduction ...............................................................................5-1

Thermoelectric potentials ..........................................................5-2

Thermoelectric generation ........................................................5-3

AC pick-up noise .......................................................................5-5

Source resistance noise ............................................................5-5

Magnetic fields ..........................................................................5-6

Radio frequency interference ....................................................5-7

Ground loops ............................................................................5-7

Shielding ...................................................................................5-9

Meter loading ..........................................................................5-10

Introduction

For sensitive measurements, external considerations affect accuracy. Effects that are not noticeable when working with higher voltages are significant in nanovolt signals.

The 2182A reads only the signal received at its input. Therefore, it is important that this signal be properly transmitted from the source.

Some of the phenomena that can cause unwanted noise include thermoelectric effects (thermocouple action), source resistance noise, magnetic fields, and radio frequency interference. The following paragraphs discuss the most important of these effects and ways to minimize them.

For comprehensive information on low-level measurements, see the Low Level Measurements Handbook, which is available from tek.com/keithley.

Section 5

Measurement considerations

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Thermoelectric potentials

Thermoelectric potentials, or thermoelectric EMFs, are the most common source of errors in low-voltage measurements. These small electric potentials are generated when different parts of the circuit are at different temperatures and when conductors made of dissimilar metals are joined.

Thermoelectric EMFs can cause the following conditions:

• Instability or zero offset is much higher than expected.

• The reading is sensitive to and responds to temperature changes. This effect can be

demonstrated by placing a heat source near the circuit or by observing changes because of sunlight or the activation of heating and air conditioning systems.

The following paragraphs discuss how thermoelectric potentials are generated and ways to minimize their effects.

Thermoelectric coefficients

The following table shows the magnitude of thermoelectric EMFs that are generated for different materials.

Material thermoelectric coefficients

Material

Thermoelectric potential

Copper-to-copper

0.2 µV/°C

Copper-to-silver

0.3 µV/°C

Copper-to-gold

0.3 µV/°C

Copper-to-cadmium/tin

0.3 µV/°C

Copper-to-lead/tin

1 µV/°C to 3 µV/°C

Copper-to-Kovar®

40 µV/°C to 75 µV/°C

Copper-to-silicon

400 µV/°C

Copper-to-copper oxide

1000 µV/°C

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Thermoelectric generation

The following figure shows a representation of how thermal EMFs are generated. The test leads are made of the A material, while the source under test is the B material. The temperatures between the junctions are shown as T1 and T2. To determine the thermal EMF generated, the following relationship may be used:

ET = QAB (T1 − T2) Where:

• E

= Generated thermal EMF

• Q

= Thermoelectric coefficient of material A with respect to material B (µV/°C)

• T

= Temperature of B junction (°C or K)

• T

= Temperature of A junction (°C or K)

In the unlikely event that the two junction temperatures are identical, no thermal EMFs are generated. More often, the two junction temperatures differ and considerable thermal EMFs are generated.

A typical test setup may have several copper-to-copper junctions. Each junction can have a thermoelectric coefficient as high as 0.2 µV/°C. Since the two materials frequently have a several degree temperature differential, several microvolts of thermal potentials can be generated even if reasonable precautions are taken.

Figure 38: Thermal EMF generation

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Minimizing thermal EMFs

To minimize thermal EMFs, use only copper wires, lugs, and test leads for the entire test setup. Also, it is imperative that all connecting surfaces are kept clean and free of oxides. As noted in

Thermoelectric generation (on page 5-3), copper-to-copper oxide junctions can result in thermal

EMFs as high as 1 mV/°C. Even when low-thermal cables and connections are used, thermal EMFs can still be a problem in

some cases. It is especially important to keep the materials that form the junction at the same temperature. One way to minimize thermal problems is to keep the two junctions close together. Also, keep all junctions away from air currents; in some cases, it may be necessary to thermally insulate sensitive junctions to minimize temperature variations. When a copper-to-copper connection is made, sufficient pressure must be applied to ensure the connection is gastight to prevent future oxidation.

In some cases, connecting the two thermal junctions together with good thermal contact to a common heat sink may be required. Unfortunately, most good electrical insulators are poor conductors of heat. In cases where such low thermal conductivity may be a problem, special insulators that combine high electrical insulating properties with high thermal conductivity may be used. Some examples of these materials include hard anodized aluminum, sapphire, and diamond.

Canceling residual thermal offsets

Even if all reasonable precautions are taken, some residual thermal offsets may still be present. These offsets can be minimized by using the 2182A relative offset feature to cancel them out. For additional information on using the relative offset feature, refer to Relative offset (on page 4-25).

If the offset voltage varies, use the dc current-reversal technique instead of relative offset. The dc current-reversal technique requires a source that can output currents equal in magnitude but opposite in polarity. In general, a voltage measurement is made on the positive and negative alternations of the current source. The averaged difference of those two readings cancels the thermal EMF component of the measurements. The 2182A can automatically make the measurements and calculate and display the result by using the delta measurement mode.

For more information on using relative offset, refer to Relative offset (on page 4-25). For information on using the dc current-reversal technique, refer to Delta (on page 6-1).

To use relative offset to cancel the residual thermal offsets:

1. Place the instrument on the 3 mV range.

2. Disconnect the cable from the source to avoid shorting out the source.

3. Short the end of the connecting cable nearest the measured source.

4. Allow the reading to settle.

5. Press the REL key.

6. Select the appropriate range and make your measurement as usual.

Model 2182A Nanovoltmeter User's Manual Section 5: Measurement considerations

2182A-900-01 Rev. C July 2022 5-5

AC pick-up noise

AC voltages that are extremely large compared with the dc signal to be measured may be induced into the input of the 2182A and corrupt the measurement. AC interference can cause the 2182A to behave in one or more of the following ways:

• Unexpected offset voltages

• Inconsistent readings between ranges

• Sudden shifts in a reading

To minimize ac pick-up, keep the test circuit source and the 2182A away from strong ac magnetic sources. The voltage induced due to magnetic flux is proportional to the area of the loop formed by the input leads. Therefore, minimize the loop area of the input leads and connect each signal at only one point.

Shielding also helps minimize ac interference. Refer to Shielding (on page 5-9) for more information.

Source resistance noise

Noise present in the source resistance is often the limiting factor in the ultimate resolution and accuracy of 2182A measurements. The following topics discuss the generation of Johnson noise and ways to minimize such noise.

Johnson noise equation

The amount of noise present in a given resistance is defined by the Johnson noise equation as follows:

Where:

• E

RMS

= The RMS value of the noise voltage

• k = Boltzmann constant (1.38 × 10

−23

joules/Kelvin)

• T = Temperature (K)

• R = Source resistance (ohms)

• F = Noise bandwidth (Hz)

At a room temperature of 293 K (20 °C), the equation simplifies to:

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5-6 2182A-900-01 Rev. C July 2022

Since the peak-to-peak noise is five times the RMS value 99% of the time, the peak-to-peak noise can be equated as follows:

For example, with a source resistance of 10 kΩ, the noise over a 0.5 Hz bandwidth at room temperature is:

Minimizing source resistance noise

You can reduce the noise in several ways:

• Reduce the source resistance

• Lower the temperature

• Narrow the bandwidth

Of these, lowering the resistance is the least practical because the signal voltage is reduced more than the noise. For example, decreasing the resistance of a current shunt by a factor of 100 also reduces the voltage by a factor of 100, but the noise is decreased only by a factor of 10.

Cooling the source is often the only practical method available to reduce noise. Again, however, the available reduction is not as large as it might seem because the reduction is related to the square root of the change in temperature. For example, to cut the noise in half, the temperature must be decreased from 293 K to 73.25 K.

Magnetic fields

When a conductor loop cuts through magnetic lines of force, a very small current is generated. This phenomenon can cause unwanted signals to occur in the test leads of a test system. If the conductor has sufficient length or cross-sectional area, even weak magnetic fields can create signals that affect low-level measurements.

To reduce these effects:

• Reduce the lengths of the connecting cables.

• Minimize the exposed circuit area.

• Change the orientation of the leads or cables.

• Minimize cable loop area or introduce cable twisting.

In extreme cases, you may require magnetic shielding. Special metal with high permeability at low flux densities (such as mu metal) is effective at reducing these effects.

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Even when the conductor is stationary, you may have problems with magnetically-induced signals. Fields can be produced by sources such as the ac power line voltage and large inductors, such as power transformers. Keep the 2182A voltage source and connecting cables away from these potential noise sources.

Radio frequency interference

Radio frequency interference (RFI) is a general term used to describe electromagnetic interference over a wide range of frequencies. RFI can be particularly troublesome at low signal levels, but it can also affect measurements at high levels if the fields are of sufficient magnitude.

Some causes of RFI are:

• Steady-state sources, such as radio or TV signals.

• Some types of electronic equipment, such as microprocessors and high-speed digital circuits.

• Impulse sources, such as arcing in high-voltage environments.

RFI can be minimized in several ways. The most obvious method is to keep the 2182A voltage source and signal leads as far away from the RFI source as possible. Additional shielding of the instrument, signal leads, sources, and other measuring instruments will often reduce RFI to an acceptable level. In extreme cases, a specially-constructed screen room may be required to sufficiently attenuate the RFI signal.

The 2182A digital filter may help to reduce RFI effects in some situations. In other cases, additional external filtering may also be required. However, filtering may have detrimental effects on the signal, such as increasing settling time.

Ground loops

When two or more instruments are connected, avoid unwanted signals caused by ground loops. Ground loops usually occur when sensitive instrumentation is connected to other instrumentation with more than one signal return path, such as power line ground. As shown in the following figure, the resulting ground loop causes current to flow through the instrument LO signal leads and then back through power line ground. This circulating current develops a small voltage between the LO terminals of the two instruments. This voltage is added to the source voltage, affecting the accuracy of the measurement.

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5-8 2182A-900-01 Rev. C July 2022

Figure 39: Power-line ground loops

The following figure shows how to connect several instruments together to eliminate this type of ground loop problem. Here, only one instrument is connected to power line ground.

Ground loops are not normally a problem with instruments like the 2182A that have isolated LO terminals. However, other instruments in the test setup may not have isolated terminals. Consult the documentation for each instrument in the test setup.

Figure 40: Eliminating ground loops

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Shielding

Proper shielding of all signal paths and sources being measured is important to minimize noise pickup in virtually any low-level measurement situation. Otherwise, interference from noise sources such as line frequency and RF fields can seriously corrupt measurements.

To minimize noise, a closed metal shield surrounding the source may be necessary, as shown in the following figure. In most cases, this shield should be connected to input LO. In some situations, better noise performance may result with the shield connected to chassis ground. The metal shield should enclose the test circuit.

Do not float input LO more than 30 V

RMS

, 42.4 V

above earth ground with an exposed

PEAK

shield connected to input LO. To avoid a possible shock hazard, surround the LO shield with a second safety shield that is insulated from the inner shield. Connect this safety shield to safety earth ground using #18 AWG minimum wire before use. Failure to adhere to these

guidelines can result in personal injury or death due to electric shock.

Figure 41: Shielding example

Tektronix 2182A Primary User

Specifications and Main Features

Frequently Asked Questions

User Manual

Safety precautions

Table of contents

Welcome

Introduction

Extended warranty

Contact information

Organization of manual sections

General ratings

Instrument power

Installation

Changing the line voltage

Line power connection

Power-up sequence

Remote communications interfaces

Programming languages

RS-232 connections

RS-232 interface selection and configuration

Flow control (signal handshaking)

GPIB setup

Install the GPIB driver software

Install the GPIB cards in your computer

GPIB bus connections

GPIB interface selection and configuration

Front-panel GPIB operation

GPIB status indicators

LOCAL key

General bus commands

DCL (device clear)

GET (group execute trigger)

GTL (go to local)

IFC (interface clear)

LLO (local lockout)

REN (remote enable)

SDC (selective device clear)

SPE, SPD (serial polling)

Transmit routines

Front-panel overview

Instrument description

1 Display annunciators

2 SHIFT key, LOCAL key, and POWER switch

3 Function keys

4 Range keys

5 Handle

6 Input connector

Rear-panel overview

1 ANALOG OUTPUT

2 TRIGGER LINK

3 RS-232

4 IEEE-488

5 Power module

Error and status messages

Default settings

Reset the instrument

Setting the number of displayed digits

Measurement overview

Making measurements

Using the front-panel display

Voltage measurements

Temperature measurements

Warm-up

ACAL (calibration)

Measuring internal temperature

Checking TCAL temperature

Test connections

Connection techniques

Model 2107 input cable

Customized connections

Voltage only connections

Single channel measurement connections

Dual-channel measurement connections

Measurement techniques

Temperature-only connections

Voltage and temperature connections

Cleaning test circuit connectors

Measuring voltage and temperature

Temperature configuration