Keithley 7708 User Manual

Model 7708 40-Channel Differential Multiplexer

with Automatic CJC User’s Guide

PA-744 Rev. C / 8-03

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.

Sales Ofﬁces: BELGIUM:

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5/03

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

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

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

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

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 Measurement Category I and Measurement Category II, as described in the International Electrotechnical Commission (IEC) Standard IEC 60664. Most measurement, control, and data I/O signals are Measurement Category I and must not be directly connected to mains voltage or to voltage sources with high transient overvoltages. Measurement 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.

that hazardous voltage is present in any unknown circuit before measuring.

is the individual or group responsible for the use

use the product for its intended function. They must be

perform routine procedures on the product

are trained to work on live circuits, and perform

A good safety practice is to expect

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,

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.

no conductive part of

5/03

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 symbol indicates a connection terminal to the equipment frame.

The

WARNING

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

The

CAUTION

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.

heading in a manual explains dangers that might

heading in a manual explains hazards that could

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.

Model 7708

Keithley Instruments, Inc.

28775 Aurora Road Cleveland, Ohio 44139 (440) 248-0400 Fax: (440) 248-6168 www.keithley.com

40-Channel Differential Multiplexer with Automatic CJC

Introduction

The Model 7708 is a 40-channel differential multiplexer card with the following features:

• DC and AC voltage measurement

• 2-wire or 4-wire Ω measurement (automatically pairs switches for four wire measurements — n + 20)

• Temperature applications (RTD, thermistor, thermocouple)

• Built-in cold junction reference

• Screw terminal connections

• Designed speciﬁcally for use with Keithley’s Model 2700, 2701, and 2750 system DMMs.

NOTE All references to the Model 27xx apply to the Models 2700, 2701, and 2750.

WARNING Before operating the Model 27xx with an accessory card, verify that the card is properly

installed and the mounting screws are tightly fastened. If the mounting screws are not properly connected, an electrical shock hazard may be present.

User’s Guide

Topic Page

Introduction

Speciﬁcations ........................................................................................................................................................................ 2

Operating instructions........................................................................................................................................................... 2

Card conﬁguration

Description............................................................................................................................................................................ 3

Card connections................................................................................................................................................................... 4

Wiring procedure .................................................................................................................................................................. 6

Typical connections .............................................................................................................................................................. 7

Connection log...................................................................................................................................................................... 9

Performance veriﬁcation

Veriﬁcation test requirements ............................................................................................................................................. 10

Test considerations.............................................................................................................................................................. 11

Veriﬁcation limits................................................................................................................................................................ 11

Recommended test equipment ............................................................................................................................................ 12

Performance veriﬁcation procedures .................................................................................................................................. 13

Calibration

Recommended test equipment ............................................................................................................................................ 23

Extender board connections................................................................................................................................................ 23

Model 7708 calibration....................................................................................................................................................... 23

Replaceable parts

Parts list............................................................................................................................................................................... 24

Ordering information .......................................................................................................................................................... 26

Factory service .................................................................................................................................................................... 26

Component layout............................................................................................................................................................... 26

PA-744 Rev. C / 8-03

Speciﬁcations

The speciﬁcations for the Model 7708 switching card are located at the end of this User’s Guide.

Operating instructions

Switching card operation is covered in the Model 27xx User’s Manual. The Model 7708 operates the same as the Model 7700 switching card with the following differences:

• The Model 7708 has 40 channels; the Model 7700 has 20 channels.

• The Model 7708 does not have any amps channels; the Model 7700 has two amps channels.

Amps measurements

The 7708 module does not support amps measurements. System channel operation cannot be used to close channels while an amps function (DCI or ICI) is selected.

If an amps function (DCI or ACI) is selected and you attempt to close a system channel, the message “NO AMPS CHAN” will be displayed brieﬂy. For remote programming, error -222 (Parameter data out of range) is generated. Example:

SYST:PRES SENS:FUNC ‘CURR:DC’ ROUT:CLOS (@101) ‘ Attempts to close system channel 101 – Generates error -222.

If a system channel is already closed and you attempt to select the DCI or ACI function, the message “INVALID FUNC” will be displayed brieﬂy. For remote programming, error -221 (Settings conﬂict) is generated. Example:

SYST:PRES ROUT:CLOS (@101) ‘ Close system channel 101. SENS:FUNC ‘CURR:DC’

Making amps measurements – In order to perform amps measurements, you must use the front panel inputs of the 27xx main-

frame. You can still use the 7708 module for other aspects of the test (such as controlling a bias supply for DUT), but you must use multiple channel operation to close channels. Example:

NOTE In order to use the front panel inputs, make sure the INPUT switch is in the out (F) position.

SYST:PRES ROUT:MULT:CLOS (@101) ‘ Closes channel 101. SENS:FUNC ‘CURR:DC’

‘ Restores system preset defaults. ‘ Selects DCI function.

‘ Restores system preset defaults.

‘ Attempts to select DCI function – Generates error -221.

‘ Restores system preset defaults.

‘ Selects DCI function – Legal operation.

Card conﬁguration

Description

Figure 1 shows a simpliﬁed schematic diagram of the Model 7708 module. As shown, the Model 7708 has channels that are

grouped into two banks of twenty channels (forty channels total). Backplane isolation is provided for each bank. Each bank also includes separate cold junction reference points. The ﬁrst bank contains channels 1 through 20 while the second bank contains channels 21 through 40. Each channel of the 40-channel multiplexer card is wired with separate inputs for HI/LO providing fully isolated inputs.

Although the Model 7708 relays are the latching type (relays hold their state even after power has been removed), all relay states are set to open a few seconds after either a power cycle or a *RST command is issued.

Connections to DMM functions are provided through the card backplane connector.

Figure 1

Simpliﬁed schematic of Model 7708

Input

Sense

Cold junction Ref x4

Channel 1

(Channels 219)

Channel 20

Cold junction Ref x5

Channel 21

(Channels 2239)

Channel 40

Channel 41

2-Pole (Open)

4-Pole (Closed)

(see Notes)

Channel 43

(see Note)

Backplane

isolation

Input

Channel 42

(see Note)

Backplane

isolation

Sense

NOTES:

Channels 4143 in this schematic refer to the designations used for control and not actual available channels.

Channels 42 and 43 can be individually controlled using multiple channel operation (ROUT:MULT commands) if the module is not to be connected to the internal DMM.

To Model 27xx Backplane

For more information on multiple channel operation, see Section 2 of the Model 27xx Users Manual.

Channel 41 (2W/4W Conﬁguration), Channel 42 (Sense Isolation), and Channel 43 (Input Isolation) are normally automatically conﬁgured by the Model 27xx. However, by using the :ROUT:MULT: commands (refer to Section 2 of the Model 27xx User’s Manual), they can be manually conﬁgured.

NOTE Connect 4-wire sense leads using channels 21–40.

To disconnect channels 21–40 from channels 1–20, send:

:ROUT:MULT:CLOS (@141) ( note opposite logic).

When automatically conﬁgured for 4-wire measurements (including 4-wire Ω , RTD temperature, Ratio, and Channel average) the channels are paired as follows:

• CH1 and CH21 • CH8 and CH28 • CH15 and CH35

• CH2 and CH22 • CH9 and CH29 • CH16 and CH36

• CH3 and CH23 • CH10 and CH30 • CH17 and CH37

• CH4 and CH24 • CH11 and CH31 • CH18 and CH38

• CH5 and CH25 • CH12 and CH32 • CH19 and CH39

• CH6 and CH26 • CH13 and CH33 • CH20 and CH40

• CH7 and CH27 • CH14 and CH34

Card connections

WARNING The information in this section is intended for qualiﬁed service personnel. Do not

attempt to perform this procedure unless qualiﬁed to do so.

Figure 2 shows how to access the screw terminals on the Model 7708. Channel designations for the screw terminals are

contained in Figure 3.

WARNING Do not exceed the maximum speciﬁcations for the Model 7708 module. Refer to the end

of this packing list for speciﬁcations.

Figure 2

Screw terminal access

LOCK

CH21

H L

CH3

CH1

CH2

CH17

CH16

CH15

H L

CH23

CH22

H L

CH4

CH18

H L

CH24

H L

CH6

CH9

CH7

CH5

CH8

CH20

CH19

H L

CH25

H L

CH35

H L

CH29

CH28

CH27

CH26

H L

CH13

CH14

CH12

CH11

CH10

CH38

CH40

CH39

CH37

CH36

H L

CH33

CH32

CH31

CH30

H L

SENSE

H L

CH34 H L

INPUT

Figure 3

Model 7708 screw terminal channel designations

CH21

H L

thru

CH1 H L

CH21

H L

CH34

H L

H L CH1

CH15

H L

thru

H L CH2

CH16

H L

CH22

H L

CH15

H L

CH14

H L CH3

CH17

H L

CH23

H L

H L CH4

CH18

H L

CH24

H L

thru

H L CH5

CH19

H L

CH25

H L

CH20

H L

H L CH6

CH20

H L

CH26

H L

H L CH7

CH27

H L

H L CH8

CH28

H L

CH9

CH35

H L

CH29

H L

CH35

H L

CH10

CH36

H L

CH30

H L

CH11

CH37

H L

CH31

H L

thru

H L

CH12

CH38

H L

CH32

H L

CH40

H L

CH13

CH39

H L

CH33

H L

CH14

CH40

H L

CH34

H L

SENSE

INPUT

Cable tie holes

INPUT

H L

and

Cable tie holes

SENSE

H L

Wiring procedure

WARNING The information in this section is intended for qualiﬁed service personnel. Do not

attempt to perform this procedure unless qualiﬁed to do so.

Use the following procedure to wire the Model 7708 module. Make all connections using the correct wire size (up to 20 AWG). Also, make sure to add supplementary insulation around the harness for voltages above 42V peak (see Figure 4).

WARNING All wiring and supplementary insulation must be rated for the maximum voltage in the

system. For example, if 1000V is applied to the front terminals of the Model 27xx, the plug-in module wiring must be rated for 1000V.

1. Make sure all power is discharged from the Model 7708 module.

2. Access the screw terminals (see Figure 2).

3. Using a small ﬂat-blade screwdriver, loosen terminal screws and install wires as desired. (Figure 4 shows connections to channels 1 and 2.)

4. Route wire along wire-path and secure with cable ties as shown.

5. Fill in a copy of the connection log (Table 1) and afﬁx it to the module cover.

6. Close and lock cover.

Figure 4

Wire dressing

H L CH1

CH15

H L

H L CH1

CH15

H L

CH21 H L

CH16

H L

H L CH2

CH16

H L

CH22

H L

H L CH2

CH17 H L

CH23

H L

H L CH3

CH17

H L

H L CH4

CH18

H L

CH24

H L

CH19 H L

CH25 H L

H L CH5

H L

CH4

CH18

H L

H L CH6

CH20

H L

CH26

H L

CH27

H L

H L CH7

CH28

H L

H L CH8

H L CH9

CH35

H L

CH29

H L

CH10

CH36

H L

CH30 H L

H L CH11

CH37

H L

CH31 H L

H L

CH12

CH38

H L

CH32

H L

CH13

CH39

H L

CH33

H L

Cable Tie

H L CH14

CH40

H L

CH34

H L

SENSE

INPUT

Cable path

for channels 1

through 20

Supplementary Insulation

Cable path

for channels 21

through 40

Ω

Typical connections

The following examples show typical wiring connections for the following types of measurements:

• Thermocouple connections, see Figure 5

• Ω 2-wire and thermistor connections, see Figure 6

• Ω 4-wire and RTD connections, see Figure 7

• Voltage (AC or DC), see Figure 8

Figure 5

Thermocouple connections

Channel 1

(Channels 2–39)

Channel 40

Figure 6

2-wire and thermistor connections

Channel 1

(Channels 2–39)

Channel 40

Thermocouples

Resistors or Thermistors

+ 23 hidden pages