Keithley 1801 Service manual

Model 1801 Nanovolt Preamp

Instruction Manual

A GREATER MEASURE OF CONFIDENCE

WARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of 1 year
from date of shipment.

Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable
batteries, diskettes, and documentation.

During the warranty period, we will, at our option, either repair or replace any product that proves to be defective.

To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in Cleveland, Ohio.
You will be given prompt assistance and return instructions. Send the product, transportation prepaid, to the indicated service
facility. Repairs will be made and the product returned, transportation prepaid. Repaired or replaced products are warranted for
the balance of the original warranty period, or at least 90 days.

LIMITATION OF WARRANTY

This warranty does not apply to defects resulting from product modification without Keithley’s express written consent, or
misuse of any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from
battery leakage, or problems arising from normal wear or failure to follow instructions.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY
IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PRO­VIDED HEREIN ARE BUYER’S SOLE AND EXCLUSIVE REMEDIES.

NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT,
INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS
INSTRUMENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE
OF THE POSSIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAMAGES SHALL INCLUDE, BUT ARE NOT LIM­ITED TO: COSTS OF REMOVAL AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY
PERSON, OR DAMAGE TO PROPERTY.

Keithley Instruments, Inc. 28775 Aurora Road • Cleveland, Ohio 44139 • 440-248-0400 • Fax: [phone]

1-888-KEITHLEY (534-8453) • www.keithley.com

Sales Offices:BELGIUM: Bergensesteenweg 709 • B-1600 Sint-Pieters-Leeuw • 02-363 00 40 • Fax: [phone]

CHINA: Yuan Chen Xin Building, Room 705 • 12 Yumin Road, Dewai, Madian • Beijing 100029 • 8610-6202-2886 • Fax: [phone]
FINLAND: Tietäjäntie 2 • 02130 Espoo • Phone: [phone] • Fax: [phone]
FRANCE: 3, allée des Garays • 91127 Palaiseau Cédex • 01-64 53 20 20 • Fax: [phone]
GERMANY: Landsberger Strasse 65 • 82110 Germering • 089/84 93 07-40 • Fax: [phone]
GREAT BRITAIN: Unit 2 Commerce Park, Brunel Road • Theale • Berkshire RG7 4AB • 0118 929 7500 • Fax: [phone]
INDIA: Flat 2B, Willocrissa • 14, Rest House Crescent • Bangalore 560 001 • 91-80-509-1320/21 • Fax: [phone]
ITALY: Viale San Gimignano, 38 • 20146 Milano • 02-48 39 16 01 • Fax: [phone]
JAPAN: New Pier Takeshiba North Tower 13F • 11-1, Kaigan 1-chome • Minato-ku, Tokyo 105-0022 • 81-3-5733-7555 • Fax: [phone]
KOREA: FL., URI Building • 2-14 Yangjae-Dong • Seocho-Gu, Seoul 137-130 • 82-2-574-7778 • Fax: [phone]
NETHERLANDS: Postbus 559 • 4200 AN Gorinchem • 0183-635333 • Fax: [phone]
SWEDEN: c/o Regus Business Centre • Frosundaviks Allé 15, 4tr • 169 70 Solna • 08-509 04 679 • Fax: [phone]
SWITZERLAND: Kriesbachstrasse 4 • 8600 Dübendorf • 01-821 94 44 • Fax: [phone]
TAIWAN: 1FL., 85 Po Ai Street • Hsinchu, Taiwan, R.O.C. • 886-3-572-9077• Fax: [phone]

2/02

Model 1801 Nanovolt Preamp Instruction Manual

©1993, Keithley Instruments, Inc.

All rights reserved.

Third Printing April 1999

Cleveland, Ohio, U.S.A.

Document Number: 1801-901-01 Rev. C

Manual Print History

The print history shown below lists the printing dates of all Revisions and Addenda created for this manual. The
Revision Level letter increases alphabetically as the manual undergoes subsequent updates. Addenda, which are
released between Revisions, contain important change information that the user should incorporate immediately
into the manual. Addenda are numbered sequentially. When a new Revision is created, all Addenda associated
with the previous Revision of the manual are incorporated into the new Revision of the manual. Each new Revi­sion includes a revised copy of this print history page.

Revision A (Document Number 1801-901-01)................................................................................ March 1993

Revision B (Document Number 1801-901-01).................................................................................... July 1995

Addendum B (Document Number 1801-901-02)........................................................................ October 1995

Revision C (Document Number 1801-901-01) .................................................................................April 1999

All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc.

Other brand and product names are trademarks or registered trademarks of their respective holders.

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 non-haz­ardous voltages, there are situations where hazardous conditions
may be present.

This product is intended for use by qualified 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 manual for complete product specifications.

If the product is used in a manner not specified, the protection pro­vided by the product 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 manual. 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, and perform

safe installations and repairs of products. Only properly trained ser­vice personnel may perform installation and service procedures.

Keithley products are designed for use with electrical signals that
are rated Installation Category I and Installation Category II, as de­scribed in the International Electrotechnical Commission (IEC)
Standard IEC 60664. Most measurement, control, and data I/O sig­nals are Installation Category I and must not be directly connected
to mains voltage or to voltage sources with high transient over-volt­ages. Installation Category II connections require protection for
high transient over-voltages often associated with local AC mains
connections. Assume all measurement, control, and data I/O con­nections are for connection to Category I sources unless otherwise
marked or described in the Manual.

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 30V RMS, 42.4V
peak, or 60VDC 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 volts, 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, make sure 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.

The instrument and accessories must be used in accordance with its
specifications and operating instructions or the safety of the equip­ment may be impaired.

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

When fuses are used in a product, replace with same type and rating
for continued protection against fire hazard.

Chassis connections must only be used as shield connections for
measuring circuits, NOT as safety earth 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.

2/02

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

!

The symbol on an instrument indicates that the user should re­fer to the operating instructions located in the manual.

The symbol on an instrument shows that it can source or mea­sure 1000 volts or more, including the combined effect of normal
and common mode voltages. Use standard safety precautions to
avoid personal contact with these voltages.

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

The CAUTION heading in a manual explains hazards that could
damage the instrument. Such damage 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 Instru­ments. Standard fuses, with applicable national safety approvals,
may be used if the rating and type are the same. 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 Instruments
to maintain accuracy and functionality of the product.) If you are
unsure about the applicability of a replacement component, call a
Keithley Instruments office for information.

To clean an instrument, use a damp cloth 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., 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.

Table of Contents

1 General Information

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

1.2 Features ........................................................................................................................................................... 1-1

1.3 Warranty information ...................................................................................................................................... 1-1

1.4 Manual addenda .............................................................................................................................................. 1-2

1.5 Safety symbols and terms ................................................................................................................................ 1-2

1.6 Specifications .................................................................................................................................................. 1-2

1.7 Unpacking and inspection ............................................................................................................................... 1-2

1.7.1 Inspection for damage ........................................................................................................................... 1-2

1.7.2 Shipment contents .................................................................................................................................. 1-2

1.7.3 Instruction manual ................................................................................................................................. 1-2

1.8 Repacking for shipment .................................................................................................................................. 1-2

1.9 Model 2001 compatibility ............................................................................................................................... 1-3

1.10 Optional accessories ........................................................................................................................................ 1-3

2 Installation

2.1 Introduction ..................................................................................................................................................... 2-1

2.2 Card configuration .......................................................................................................................................... 2-2

2.2.1 Preamplifier module .............................................................................................................................. 2-2

2.2.2 Power supply card ................................................................................................................................. 2-3

2.3 Power supply card preparation ........................................................................................................................ 2-4

2.4 Power supply card installation and removal ................................................................................................... 2-5

2.4.1 Card installation ..................................................................................................................................... 2-5

2.4.2 Card removal ......................................................................................................................................... 2-5

2.5 Connections ..................................................................................................................................................... 2-6

2.5.1 Power supply connections ..................................................................................................................... 2-6

2.5.2 Output connections to multimeter ......................................................................................................... 2-7

2.5.3 Input signal connections ........................................................................................................................ 2-7

2.6 Operating considerations ................................................................................................................................. 2-9

2.6.1 Using the thermal isolation container .................................................................................................... 2-9

2.6.2 Minimum operating distance ................................................................................................................. 2-9

i

3 Operation

3.1 Introduction ..................................................................................................................................................... 3-1

3.2 Preamplifier operation .................................................................................................................................... 3-1

3.2.1 Power-up detection ................................................................................................................................ 3-1

3.2.2 Preamplifier configuration menu ........................................................................................................... 3-2

3.2.3 Enabling Model 1801 operation ............................................................................................................ 3-2

3.2.4 Preamp ON/OFF states .......................................................................................................................... 3-2

3.2.5 Preamplifier filtering ............................................................................................................................. 3-4

3.2.6 Operational differences ......................................................................................................................... 3-5

3.2.7 IEEE-488 bus operation ........................................................................................................................ 3-7

3.3 Measurements ................................................................................................................................................. 3-7

3.3.1 DC voltage measurements ..................................................................................................................... 3-7

3.3.2 AC voltage measurements ..................................................................................................................... 3-9

3.3.3 Four-wire resistance measurements .................................................................................................... 3-11

3.3.4 Frequency measurements .................................................................................................................... 3-11

3.3.5 Differential thermocouple temperature measurements ....................................................................... 3-14

3.4 Measurement considerations ......................................................................................................................... 3-18

3.4.1 Thermoelectric potentials .................................................................................................................... 3-18

3.4.2 Source resistance noise ........................................................................................................................ 3-20

3.4.3 Magnetic fields .................................................................................................................................... 3-21

3.4.4 Electromagnetic interference (EMI) .................................................................................................... 3-22

3.4.5 Ground loops ....................................................................................................................................... 3-22

3.4.6 Shielding .............................................................................................................................................. 3-22

4 Performance V erification

4.1 Introduction ..................................................................................................................................................... 4-1

4.2 Environmental conditions ............................................................................................................................... 4-1

4.3 Warm-up period .............................................................................................................................................. 4-2

4.4 Line power ...................................................................................................................................................... 4-2

4.5 Recommended test equipment ........................................................................................................................ 4-2

4.6 Verification limits ........................................................................................................................................... 4-2

4.7 Restoring default conditions ........................................................................................................................... 4-3

4.8 Verification procedures ................................................................................................................................... 4-3

4.8.1 DC volts verification ............................................................................................................................. 4-3

4.8.2 AC volts verification ............................................................................................................................. 4-6

4.8.3 Resistance verification .......................................................................................................................... 4-6

5 Service Information

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

5.2 Calibration ...................................................................................................................................................... 5-1

5.2.1 Environmental conditions ..................................................................................................................... 5-1

5.2.2 Warm-up period .................................................................................................................................... 5-1

5.2.3 Line power ............................................................................................................................................. 5-2

5.2.4 Recommended calibration equipment ................................................................................................... 5-2

5.2.5 Offset adjustments ................................................................................................................................. 5-2

5.2.6 Normal calibration ................................................................................................................................. 5-4

5.2.7 Gain constants calibration ..................................................................................................................... 5-9

ii

5.3 Principles of operation .................................................................................................................................. 5-10

5.3.1 Block diagram ...................................................................................................................................... 5-10

5.3.2 Preamplifier module ............................................................................................................................ 5-10

5.3.3 Power supply cable .............................................................................................................................. 5-10

5.3.4 Power supply card ............................................................................................................................... 5-10

5.4 Special handling of static-sensitive devices .................................................................................................. 5-12

5.5 Troubleshooting ............................................................................................................................................ 5-12

5.5.1 Troubleshooting equipment ................................................................................................................. 5-12

5.5.2 Troubleshooting access ........................................................................................................................ 5-12

5.5.3 Troubleshooting procedure .................................................................................................................. 5-12

6 Replaceable Parts

6.1 Introduction ..................................................................................................................................................... 6-1

6.2 Parts lists ......................................................................................................................................................... 6-1

6.3 Ordering information ...................................................................................................................................... 6-1

6.4 Factory service ................................................................................................................................................ 6-1

6.5 Component layouts and schematic diagrams .................................................................................................. 6-1

A Specifications

B Calibration Programs

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

Program requirements .................................................................................................................................... B-1

General program instructions ......................................................................................................................... B-1

C IEEE-488 Bus Command Summary

iii

List of Illustrations

2 Installation

Figure 2-1 Preamplifier module configuration ..................................................................................................... 2-2

Figure 2-2 Power supply card configuration ........................................................................................................ 2-3

Figure 2-3 Power and output connections ............................................................................................................ 2-4

Figure 2-4 Typical analog output connections ..................................................................................................... 2-5

Figure 2-5 Power supply card installation ............................................................................................................ 2-6

Figure 2-6 Power supply connections .................................................................................................................. 2-7

Figure 2-7 Connections to multimeter input ........................................................................................................ 2-8

Figure 2-8 Input cable connections ...................................................................................................................... 2-8

Figure 2-9 Using the thermal isolator container ................................................................................................... 2-9

3 Operation

Figure 3-1 Filter frequency response curves ........................................................................................................ 3-5

Figure 3-2 Connections for DC voltage measurements ....................................................................................... 3-8

Figure 3-3 Connections for AC voltage measurements ..................................................................................... 3-10

Figure 3-4 Connections for 4-wire resistance measurements ............................................................................. 3-12

Figure 3-5 Connections for frequency measurements ........................................................................................ 3-13

Figure 3-6 Connections for differential temperature measurements .................................................................. 3-16

Figure 3-7 Thermal EMF generation .................................................................................................................. 3-19

Figure 3-8 Magnetic field generation ................................................................................................................. 3-21

Figure 3-9 Minimizing interference from magnetic loops ................................................................................. 3-21

Figure 3-10 Power line ground loops ................................................................................................................... 3-23

Figure 3-11 Eliminating ground loops ................................................................................................................. 3-24

4 Performance Verification

Figure 4-1 Connections for DC volts verification ................................................................................................ 4-4

Figure 4-2 Connections for AC volts verification ................................................................................................ 4-7

5 Service Information

Figure 5-1 Connections for offset voltage adjustment ......................................................................................... 5-3

Figure 5-2 Connections for offset current adjustment .......................................................................................... 5-3

Figure 5-3 Calibration connections ...................................................................................................................... 5-5

Figure 5-4 Block diagram ................................................................................................................................... 5-11

v

List of Tables

3 Operation

Table 3-1 Power-up error messages .................................................................................................................... 3-2

Table 3-2 CONFIGURE PREAMP menu structure ............................................................................................ 3-3

Table 3-3 Preamp ON/OFF states ....................................................................................................................... 3-3

Table 3-4 Filter response parameters .................................................................................................................. 3-4

Table 3-5 Preamplifier measurement ranges ....................................................................................................... 3-6

Table 3-6 Factory default conditions .................................................................................................................. 3-6

Table 3-7 Preamplifier configuration commands ............................................................................................... 3-7

Table 3-8 CONFIG TEMPERATURE menu with Model 1801 enabled ......................................................... 3-14

Table 3-9 Differential temperature bus commands ........................................................................................... 3-18

Table 3-10 Thermoelectric coefficients .............................................................................................................. 3-18

4 Performance Verification

Table 4-1 Recommended test equipment for performance verification .............................................................. 4-2

Table 4-2 Limits for DC volts verification ......................................................................................................... 4-5

Table 4-3 Limits for AC voltage verification ..................................................................................................... 4-6

5 Service Information

Table 5-1 Recommended equipment for calibration ........................................................................................... 5-2

Table 5-2 Model 1801 IEEE-488 bus calibration commands ............................................................................. 5-7

Table 5-3 IEEE-488 bus calibration summary .................................................................................................... 5-7

Table 5-4 Preamplifier calibration errors ............................................................................................................ 5-9

Table 5-5 Recommended troubleshooting equipment ...................................................................................... 5-12

Table 5-6 Power supply card troubleshooting procedure ................................................................................. 5-13

6 Replaceable Parts

Table 6-1 Electrical, Parts List ............................................................................................................................ 6-2

Table 6-2 Mechanical, Parts List ........................................................................................................................ 6-3

C IEEE-488 Bus Command Summary

Table C-1 IEEE-488 bus command summary..................................................................................................... C-1

Ω

Ω

1

General Information

1.1 Introduction

This section contains general information about the
Model 1801 Nanovolt Preamp option for the Model 2001
Multimeter. The Model 1801 adds 20µV, 200µV , and 2mV
DC volts and 500µV RMS AC voltage measurement
ranges to the Model 2001 and includes 2m
200

4-wire resistance ranges. The Model 1801 can also
be used for frequency and differential thermocouple tem­perature measurements.

Section 1 is arranged in the following manner:

1.2 Features

1.3 Warranty information

1.4 Manual addenda

1.5 Safety symbols and terms

1.6 Specifications

1.7 Unpacking and inspection

1.8 Repacking for shipment

1.9 Model 2001 compatibility

1.10 Optional accessories

1.2 Features

The Model 1801 is designed to be used with the Model
2001 Multimeter. Key features include:

through

• High sensitivity: The Model 1801 increases the DC
voltage measurement sensitivity of the Model 2001
by a factor of 10,000.

• Low noise: Excellent noise rejection ensures minimal
noise effects on the measurement.

• Low-thermal input connections: Copper-to-copper
input connections are used to minimize offsets caused
by thermal EMFs.

• Thermal isolation enclosure: An insulated enclosure
is supplied for the preamplifier in order to minimize
the effects of temperature variations.

• Integrated operation: Automatic power-up detection
of the Model 1801 integrates range and function
selection and reading display from the Model 2001
Multimeter front panel. Model 1801 operation can be
enabled or disabled with a front panel menu selection.

1.3 Warranty information

Warranty information is located on the inside front cover
of this instruction manual. Should your Model 1801
require warranty service, contact the Keithley representa­tive or authorized repair facility in your area for further
information. When returning the preamplifier for repair,
be sure to fill out and include the service form at the back
of this manual in order to provide the repair facility with
the necessary information.

1-1

General Information

1.4 Manual addenda

Any improvements or changes concerning the preampli­fier or manual will be explained in an addendum included
with unit.

1.5 Safety symbols and terms

The following symbols and terms may be found on an
instrument or used in this manual.

!

The symbol on an instrument indicates that the user
should refer to the operating instructions located in the
instruction manual.

WARNING heading used in this manual explains

The
dangers that might result in personal injury or death.
Always read the associated information very carefully
before performing the indicated procedure.

NOTE

Be careful not to throw away the foam
thermal isolation enclosure, which is
intended for use with the preamplifier
module.

1.7.2 Shipment contents

The following items are included with every Model 1801
order:

• Power supply card

• Preamplifier module

• 3-meter power supply connecting cable

• 3-meter low-thermal input cable

• Low-thermal copper shorting strap

• Thermal isolation enclosure

• Model 1801 Instruction Manual

CAUTION heading used in this manual explains

The
hazards that could damage the preamplifier . Such damage
may invalidate the warranty.

1.6 Specifications

Model 1801 specifications are located in Appendix A.
These specifications include Model 2001 Multimeter
specifications and assume that the Model 2001 is properly
calibrated.

1.7 Unpacking and inspection

1.7.1 Inspection for damage

Upon receiving the Model 1801, carefully unpack all
items from the shipping carton, and inspect for physical
damage. Report any such damage to the shipping agent
immediately. Save the packing carton in case the unit
must be shipped in the future.

• Additional accessories as ordered

1.7.3 Instruction manual

If an additional Model 1801 Instruction Manual is
required, order the manual package, Keithley part number
1801-901-00. The manual package includes an instruction
manual and any pertinent addenda.

1.8 Repacking for shipment

Should it become necessary to return the Model 1801 for
repair, carefully pack the preamplifier , po wer supply card,
and power cable in the original packing carton or the
equivalent, and include the following information:

• Advise as to the warranty status of the unit.

• Write ATTENTION REPAIR DEPARTMENT on the
shipping label.

• Fill out and include the service form located at the
back of this manual.

1-2

General Information

1.9 Model 2001 compatibility

The Model 1801 can be used only with Model 2001 Mul­timeters with main microcontroller revision B01 or later
firmware. The firmware re vision level is displayed during
the power-up cycle (the main microcontroller firmware
revision level appears on the left). The firmware revision
level may also be displayed by using the front panel
MENU/GENERAL/SERIAL# selection.

If an earlier version is displayed (Ann), contact your
Keithley sales representati ve regarding an upgrade to your
Model 2001 DMM.

1.10 Optional accessories

Model 1483 Low-Thermal Connection Kit

The Model 1483 contains a crimp tool, pure copper lugs,
alligator clips, and assorted hardware.

Model 1484 Refill Kit

The Model 1484 includes the following replacement parts
for the Model 1483: pure copper lugs, alligator clips, and
assorted hardware.

1-3

2

Installation

2.1 Introduction

This section includes information on installing the Model
1801 in the Model 2001 Multimeter and making power
supply and output connections.

This section is arranged as follows:

2.2 Card configuration: Discusses the overall configu-

ration of both the preamplifier module and the
power supply card.

2.3 Power supply card preparation: Covers connect-

ing the power supply cable to the card and routing
the output leads through the cable clamp.

2.4 Card installation and removal: Gives the proce-

dure to install the power supply card assembly in
the Model 2001 Multimeter and describes how to
remove the card.

2.5 Connections: Covers the basics for connecting the

power supply to the preamplifier module, as well as
multimeter input connections and analog output
connections.

2.6 Operating considerations: Outlines use of the ther-

mal isolation enclosure and discusses minimum
operating distance.

2-1

Installation

2.2 Card configuration

2.2.1 Preamplifier module

Figure 2-1 shows the configuration of the preamplifier
module. Key items include:

❶

INPUT Terminals

The HI and LO INPUT terminals are pure copper studs
and nuts intended for connecting input signals to the
Model 1801. To minimize thermal EMFs, use only pure
copper lugs or wires for connections, and be sure that both
the terminals and connecting lugs are clean and free of
oxidation. See paragraph 2.4.4 for details on input
connections.

CAUTION

The maximum signal between
INPUTS HI and LO is 1V @ 100mA
peak (inputs over 2mV require one­minute recovery). The maximum volt-

age between LO and chassis ground is
41V peak. Exceeding these limits may
result in damage.

❷

Offset Adjustments

V ZERO and I ZERO are externally accessible
adjustments for nulling voltage and current offsets
respectively. These controls need not be adjusted during
normal operation.

NOTE

Improper offset adjustments will
degrade performance. The offset adjust­ments should only be performed using
the procedures covered in Section 5.

Power Supply Connector

❸

This connector attaches the preamplifier module to the
power supply card using the supplied cable. See para­graph 2.4.1 for details.

KEITHLEY

INPUTS

HI

2mV

PEAK

LO

41V

PEAK

Input

1

Terminals

Figure 2-1

Preamplifier module configuration

1801 NANOVOLT PREAMP

V ZERO

I ZERO

CAUTION:

NO INTERNAL OPERATOR SERVICEABLE PARTS,
SERVICE BY QUALIFIED PERSONNEL ONLY.

Zero

2

Adjustments

!

Power Supply

3

Connector

2-2

2.2.2 Power supply card

Figure 2-2 shows the configuration of the power supply
card. Components include:

Cover

❶

The plastic cover shields circuit board parts from damage
and contamination. In order to open the cover , press in on
the cover latch, then swing the cover open on its hinges.

Analog Output

❷

The analog output terminals are intended for connecting
the preamplifier output to a monitoring device such as a
chart recorder. See paragraph 2.3 for details.

Power Connector

❸

The power connector and connecting cable supply power
and control signals to the preamplifier module. They also
feed the analog output signal back to the power supply
card.

Installation

❹

Cable Clamp

The cable clamp provides a strain relief for the output
leads and power cable.

Output Leads

❺

The two output leads are terminated with banana plugs
intended to connect to the multimeter input jacks. Red is
HI, and black is LO. See paragraph 2.5.2 for information
on output connections.

❻

Shield Jumper

This jumper allows you to connect the cable shield and
preamplifier shell either to earth ground or to input LO.
Installing the jumper in the earth ground position allows
the unit to meet its stated low common-mode current but
will degrade common-mode noise rejection (if an AC sig­nal is floating on input LO). Installing the jumper in the
LO position will degrade the common-mode current but
will provide the specified common-mode noise rejection.

Cover
Latch

Figure 2-2

Power supply card configuration

1

Cover

LO
Earth

2

Analog

6

Output

Shield Jumper

(W101)

3

Power
connections

5

Output Leads

Cable Clamp

4

2-3

Installation

2.3 Power supply card preparation

Power and output connections

Before installing the power supply card in the multimeter ,
make sure the power cable is connected to the po wer con­nector (see Figure 2-3).

Shield jumper

The shield jumper connects the cable shield and preamp
shell either to earth ground or input LO. This jumper
should be installed as follows:

• If low common-mode current is more important than
common-mode noise rejection, place the jumper in
the earth ground position.

• If common-mode noise rejection is more important
than low common-mode current, place the jumper in
the LO position.

Analog output connections

The analog output terminals, which are located on the
power supply board, provide a 0-2V full scale output for
monitoring devices such as chart recorders.

Since the analog output signal is at a relatively high level
and has low source impedance, the type of wiring used for
connections is not critical. Standard stranded wire of the
type used for DMM test leads should be adequate in most
cases. Figure 2-4 shows typical analog output
connections.

Note that the common-mode current (from LO to earth
ground) of any device connected to the analog output ter­minals will be added to that of the Model 1801/2001. T yp­ical common-mode current levels for a DMM or chart
recorder are several micro amps or higher.

Figure 2-3

Power and output connections

Output Connections

To Preamp

Power

Connections

2-4

Figure 2-4

Typical analog output connections

Installation

Analog output terminals

HI
LO

Monitoring device

(e.g., chart recorder)

2.4 Power supply card installation and removal

This paragraph explains how to install and remove the
Model 1801 power supply card assembly in the Model
2001 Multimeter.

2.4.1 Card installation

Perform the following steps, and refer to Figure 2-5 to
install the power supply card assembly in the Model 2001
Multimeter:

WARNING

Turn off the Model 2001 Multimeter,
and disconnect the line cord before inst
alling or removing the power supply
card.

1. Remove the cover plate labeled OPTION SLOT on
the rear panel of the Model 2001 Multimeter. To do

so, pry out the two fasteners, then remove the cover
plate.

2. Slide the po wer supply card edges into the guide rails
inside the multimeter.

3. With the ejector arms in the unlocked position, care­fully push the card all the way forward until the arms
engage the ejector cups. Push both arms inward to
lock the card into the multimeter.

4. After installation, connect the power cable to the
preamp module and the output leads to the multime­ter as discussed in paragraph 2.5 below.

2.4.2 Card removal

Follow the steps below to remove the power supply card
from the multimeter:

1. Unlock the card by pulling the latches outward.

2. Carefully slide the card out of the multimeter.

3. If the multimeter is to be operated without the power
supply card installed, install the OPTION SLOT
cover plate.

2-5

Installation

Unlock card

Ejector Arms (2)

Lock card

Figure 2-5

Power supply card installation

2.5 Connections

This paragraph provides the information necessary to
connect the preamplifier module to the power supply card
and multimeter.

2-6

2.5.1 Power supply connections

After installing the power supply in the multimeter, con­nect the preamplifier to the power supply card using the
supplied connecting cable, as shown in Figure 2-6.

Preamplifier
Module

Insert Plug in
Connector

Power Supply
Cable

Power Supply
Card

Installation

Figure 2-6

Power supply connections

CAUTION

Turn off the Model 2001 Multimeter
power before connecting or discon­necting the cable.

2.5.2 Output connections to multimeter

After installation, connect the output leads to the Model
2001 rear panel input jacks, as shown in Figure 2-7. For
DCV, ACV, frequency, and temperature measurements,
the red lead should be connected to INPUT HI, and the
black lead should be connected to INPUT LO.

NOTE

Be sure to select the rear inputs with the
front panel INPUTS switch when using
the Model 1801. Output connections for
4-wire resistance measurements must be
changed, as explained in paragraph 3.3.2
in Section 3.

• Use only shielded low-thermal cables such as the
input cable supplied with the Model 1801.

• Use only crimped-on copper lugs and copper wires
for all input connections. Crimping results in an air­tight connection.

• Copper-to-copper oxide connections result in
thermoelectric potentials as high as 1000µV/°C (see
paragraph 3.4.1). To avoid these thermals, make sure
that all connections are clean and free of oxides.
Scotchbrite® copper cleaner can be used to clean
connections.

• Do not handle the prepared ends of the input cable.
Body oils and salts can result in contamination,
affecting connection integrity.

CAUTION

To avoid possible preamplifier dam­age, keep static electricity discharge
away from input terminals.

2.5.3 Input signal connections

Input connections are made directly to the two preampli­fier screw terminals, as shown in Figure 2-8. When mak­ing input connections, observe the following precautions
in order to minimize noise pickup and thermal EMFs:

The supplied input cable can be used for most measure­ment functions, but some such as thermocouple measure­ments may require different connecting wires. For input
connection information specific to the type of measure­ment function, refer to paragraph 3.3 in Section 3.

2-7

Installation

Input HI

HI (Red)

NOTES: 1. See paragraph 3.3.3
for 4-wire resistance
output connections.

2. Select rear inputs
using front panel
switch.

Input LO

LO (Black)

Figure 2-7

Connections to multimeter input

HI

DUT

LO

Noise Shield

Red

Low-Thermal
Input Cable

Black

Figure 2-8

Input cable connections

1801 NANOVOLT PREAMP

V ZERO
I ZERO

CAUTION:

NO INTERNAL OPERATOR SERVICEABLE PARTS,
SERVICE BY QUALIFIED PERSONNEL ONLY.

!

Red

Black

KEITHLEY

INPUTS

HI

2mV

PEAK

LO

41V

PEAK

NOTE : 1. Use only clean copper-to-copper connections.

2. See paragraph 3.3 for specific connections

each measurement function.

2-8

Installation

2.6 Operating considerations

2.6.1 Using the thermal isolation container

After making all connections, place the preamplifier mod­ule in the thermal isolation container, as shown in Figure
2-9. Route the connecting wires through the slits in each
end of the container, then cover the preamplifier with the
lid. Allow the preamplifier to thermally stabilize for at
least one hour to achieve rated accuracy.

Preamplifier Module

KEITHLEY

INPUTS

HI

2mV

PEAK

LO

41V

PEAK

1801 NANOVOLT PREAMP

2.6.2 Minimum operating distance

The Model 1801 preamplifier module should be kept a
minimum of two feet away from the Model 2001 Multi­meter and other instrumentation to avoid noise pickup due
to stray magnetic fields.

Foam Thermal
Insolation Container

V ZERO
I ZERO

CAUTION:

NO INTERNAL OPERATOR SERVICEABLE PARTS,
SERVICE BY QUALIFIED PERSONNEL ONLY.

!

Route
Input cable
through slit

Figure 2-9

Using the thermal isolator container

Route Power
Supply cable
through slit

2-9

3

Operation

3.1 Introduction

This section contains basic information on operating the
Model 1801 using the host Model 2001 Multimeter. For
more detailed information on operating the Model 2001
Multimeter, see the Model 2001 Operator’s Manual.

This section is organized as follows:

3.2 Preamplifier operation: Covers enabling Model

1801 operation, preamplifier filtering, operating
restrictions, and summarizes IEEE-488 bus
operation.

3.3 Measurements: Discusses DC and AC voltage

measurements, and 4-wire resistance and thermo­couple temperature measurements.

3.4 Measurement considerations: Explains a number

of considerations that may apply to Model 1801
measurements.

3.2 Preamplifier operation

3.2.1 Power-up detection

If, however, the preamplifier is enabled at power-on, the
unit will display the following message:

Preamp ON

Whether the Model 1801 is enabled or disabled at power­on depends on the programmed power-on setup:

• GPIB defaults: Model 1801 always disabled.

• Bench defaults: Model 1801 always enabled.

• User setup: Model 1801 either enabled or disabled
depending on the state stored in the recalled setup.

See paragraph 3.2.5 for additional information on saving
and recalling setups. Paragraph 3.12.1 of the Model 2001
Operator’s Manual explains how to select the instrument
setup that goes into effect at power-on.

Note that you can query the instrument over the IEEE-488
bus to determine if the Model 1801 is present by using the
*OPT? query. If the preamplifier is present, the instru­ment will return the following response:

The Model 2001 Multimeter automatically detects the
presence of the Model 1801 at power-on. The instrument
will indicate the presence of the Model 1801 by display­ing the following message if the preamplifier is disabled:

Preamp OFF

2001-1801

Refer to paragraph 4.9 of the Model 2001 Multimeter
Operator’s Manual for more details on using the *OPT?
query.

3-1

Operation

Power-up error messages

T able 3-1 summarizes error messages that may occur dur ­ing power-up when the Model 1801 is installed.

3.2.2 Preamplifier configuration menu

Table 3-2 summarizes the preamplifier configuration
menu structure. In order to access this menu, press the
front panel CHAN key.

3.2.3 Enabling Model 1801 operation

Follow the procedure below to enable Model 1801
operation:

1. Press the CHAN key. The Model 2001 will display
the following:

CONFIGURE PREAMP

CONTROL FILTER CALIBRATION

3. Select ENABLE, then press ENTER.

4. Press EXIT to return to normal display. The unit will
display the following message to indicate that the
preamplifier is enabled:

Preamp ON

5. To disable the preamplifier, repeat steps 1 through 4,
but select DISABLE in the PREAMP CONTROL
menu. The unit will display the following to indicate
that the preamplifier is disabled:

Preamp OFF

NOTE

Once Model 1801 operation is enabled,
readings will be scaled accordingly . Dis­able Model 1801 operation if you intend
to make measurements without the
Model 1801. Otherwise, incorrect read­ings will be displayed.

2. Select CONTROL, then press ENTER. The unit will
display the following:

PREAMP CONTROL

ENABLE DISABLE

Table 3-1

Power-up error messages

Error number Message Description

-315
+516
+517

“Preamp memory lost”
“Installed option id lost”
“Preamp calibration data lost”

3.2.4 Preamp ON/OFF states

Table 3-3 summarizes operating states the Model 2001
will assume when the preamp is turned on or off.

Cannot recover preamp setup due to corrupt memory.
Cannot identify Model 1801 as installed option.
Preamplifier uncalibrated due to lost cal constants.

3-2

Table 3-2

CONFIGURE PREAMP menu structure

Menu item Description

Operation

CONTROL

ENABLE
DISABLE

FILTER

FAST
MEDIUM
SLOW

CALIBRATION

CALIBRATION-DATES
CALIBRATE
ENTER-CAL-CONSTANTS

NOTE: Press CHAN key to access CONFIGURE PREAMP menu. See Section 5 for

calibration information.

Table 3-3

Preamp ON/OFF states

Enable/disable preamplifier.

Enable preamplifier.
Disable preamplifier.

Select preamplifier filter.

Select fast response filter.
Select medium response filter.
Select slow response filter.

Calibrate preamplifier.

Set calibration dates.
Calibrate preamplifier.
Input calibration constants.

Mode Preamp ON Preamp OFF

DCV Range
DCV Auto-range

ACV Range
ACV Auto-range
ACV Type

Ω4W Range
Ω4W Auto-range

FREQ Voltage Threshold Range
FREQ Voltage Threshold Level

TEMP Transducer

NOTE: This table lists operating states that change when preamp is enabled or disabled. All other

states are unaffected by enabling or disabling preamp.

2mV
OFF

500µV
OFF
Low-frequency RMS

200Ω
OFF

2mV
0

Differential thermocouple

1000V
ON

750V
ON
Normal RMS

200kΩ
ON

1V
0

4-wire RTD

3-3

Operation

3.2.5 Preamplifier filtering

The Model 1801 has three analog filters with FAST,
MEDIUM, and SLOW responses respectively. These fil­ters are in addition to the Model 2001 filter, which can
also be used with the preamplifier. See paragraph 3.9 of
the Model 2001 Operator’s Manual for details on Model
2001 filtering.

The following paragraphs discuss selecting the filter
response and also cover filter frequency response curves.
See the specifications in Appendix A for filter settling
times.

Selecting filter response

1. Press the CHAN key to bring up the preamplifier
configuration menu. The instrument will display the
following:

CONFIGURE PREAMP

CONTROL FILTER CALIBRATION

2. Select FILTER, then press ENTER. The unit will dis­play filter response selections:

SELECT PREAMP FILTER

FAST MEDIUM SLOW

3. Select the desired filter response, then press ENTER.
The FAST response filter provides the least noise
reduction and fastest response, while the SLOW
response filter gives the most noise reduction and
slowest response. Note that only the FAST response
filter is available with the ACV and FREQ functions.

4. Press EXIT to return to normal display.

Filter frequency response curves

Each of the preamplifier filters exhibits single-pole, low­pass response. In addition to the filter selection, filter
response also depends on the selected range, as summa­rized in Table 3-4. The table includes the -3dB response
point for each set of operating conditions, as well as a fil­ter response number. The filter frequency response num­ber corresponds to the equivalent curve number shown in
Figure 3-1. Note that the filter response curves shown are
for the preamplifier only and do not include Model 2001
response, which is affected by its own filter parameters as
well as the selected integration period.

Table 3-4

Filter response parameters

Filter response

FAST MEDIUM SLOW

Function and Range

DCV: 20µV

-3dB
bandwidth

40Hz 3 0.32Hz 6 0.032Hz 7

Filter
number

-3dB
bandwidth

Filter
number

-3dB
bandwidth

Ω4W None
DCV: 200µV

185Hz 2 3.2Hz 5 0.32Hz 6

Ω4W: 2mΩ
DCV: 2mV

700Hz 1 32Hz 4 3.2Hz 5

Ω4W: 20mΩ–200Ω

NOTE: Filter numbers correspond to curves shown in Figure 3-1. FAST filter only for ACV and FREQ functions.

10%-90% risetime = 0.35/Bandwidth (Hz)
τ (s) = 0.15/Bandwidth (Hz)

Filter
number

3-4

-10

-20

-30

Operation

0

-40

dB

Gain

-50

-60

-70

-80

-90

-100

0.001 0.01 0.1 1 10 100 1k 10k 100k

NOTE : Response curves are for preamplifier only.
Number corresponds to conditions listed in
Table 3-4.

Figure 3-1

Filter frequency response curves

3.2.6 Operational differences

Functions

Frequency (Hz)

select one of these functions when the Model 1801 is
enabled:

1
2

3

4

5

67

The following functions are available when using the
Model 1801:

• DC volts

• AC volts (low-frequency RMS only)

• 4-wire ohms

• Frequency (voltage only)

• Thermocouple temperature (differential only)

Note that DC current, AC current, and 2-wire ohms func­tions are not available when the preamp is turned on. The
following message will be displayed if you attempt to

Function is not available with Preamp enabled

Ranging

Table 3-5 summarizes the measurement ranges available
when using the Model 1801. Note that auto-ranging can­not be used when the preamplifier is enabled. If you
attempt to use auto-ranging with the preamp turned on,
the instrument will display the following message:

Auto-ranging is not available with Preamp enabled

3-5