Keithley 7708 User Manual

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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

Figure 7

4-wire and RTD connections

Channel 1

(Channels 2–19)

Channel 20

Channel 21

Resistor or 4-Wire RTD

Ω

(Channels 22–39)

Channel 40

Figure 8

Voltage connections (DC or AC)

Channel 1

(Channels 2–39)

Channel 40

DC Voltage AC Voltage

Connection log

Make a copy of Table 1 and afﬁx it to the cover of the Model 7708. Use this to record connection information and channel descriptions as needed.

Table 1

Connection log Model 7708

Channel Color Description Description Color Channel

INPUT

SENSE

CH1

CH2

CH3

CH4

CH5

CH6

CH7

CH8

CH9

CH10

CH11

CH12

CH13

CH14

CH15

CH16

CH17

CH18

CH19

CH20

H L H L HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL HH LL

CH21

CH22

CH23

CH24

CH25

CH26

CH27

CH28

CH29

CH30

CH31

CH32

CH33

CH34

CH35

CH36

CH37

CH38

CH39

CH40

Performance veriﬁcation

The performance of the Model 7708 card is tested by verifying measurement accuracy through the card. If veriﬁcation limits are met through the front panel terminals of the Model 27xx, they should also be met through the card.

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

attempt these procedures unless you are qualiﬁed to do so.

NOTES Measurement accuracy through the Model 7708 card should only be veriﬁed after instrument

accuracy has already been veriﬁed through the front panel terminals of the Model 27xx. The procedures to verify accuracy from the front panel inputs are provided in the Model 2700 Service Manual.

If the Model 7708 card is still under warranty and is the cause of measurement inaccuracy, contact your Keithley representative or the factory to determine the correct course of action.

Model 7708 veriﬁcation test procedures include:

• DC volts

• AC volts

• Resistance

• Temperature

• Frequency

• Ratio and average

Veriﬁcation test requirements

Be sure that you perform the veriﬁcation tests:

• Under the proper environmental conditions.

• After the speciﬁed warm-up period.

• Using the correct line voltage.

• After restoring factory defaults.

• With the INPUTS switch in the REAR (in) position.

Also, make sure to use the proper calibration equipment (Table 2) and the reading limits provided with the veriﬁcation procedures.

Environmental conditions

Conduct your performance veriﬁcation procedures in a test environment that has:

• An ambient temperature of 18° to 28°C (65° to 82°F).

• A relative humidity of less than 80% unless otherwise noted.

Warm-up period

Allow the Model 27xx to warm up for at least two hours before conducting the veriﬁcation procedures.

If the instrument has been subjected to temperature extremes (those outside the ranges stated above), allow additional time for the instrument’s internal temperature to stabilize. Typically, allow one extra hour to stabilize a unit that is 10°C (18°F) outside the speciﬁed temperature range.

Also, allow the test equipment to warm up for the minimum time speciﬁed by the manufacturer.

Line power

The Model 27xx requires a line voltage of 100V/120V/220V/240V, ±10% and a line frequency of 47.5Hz to 63Hz. Note that the line frequency is automatically sensed at power-up, but the line voltage must be manually set to either 100V/120V or 220V/240V as described in Section 3 of the Model 27xx Service Manual.

Factory defaults

Before performing the veriﬁcation procedures, restore the instrument to its factory defaults as follows:

1. Press SHIFT and then SETUP. The instrument will display the following prompt:

RESTORE: FACT.

2. Using either range key, select FACT, then restore the factory default conditions by pressing ENTER.

INPUTs switch

In order to connect the Model 7708 card to the meter of the Model 27xx, the INPUTs switch must be in the REAR (in) position. The INPUTS switch is located on the front panel of the Model 27xx multimeter near the input terminals.

Test considerations

When performing the veriﬁcation procedures:

• Be sure to restore factory defaults as outlined above.

• Make sure that the equipment is properly warmed up and connected to the correct input terminals. Also make sure that the INPUTS switch is in the REAR (in) position.

• Do not use autoranging for any veriﬁcation tests because autorange hysteresis may cause the Model 27xx to be on an incorrect range. For each test signal, you must manually set the correct range for the Model 27xx using the range keys.

• Make sure the calibrator is in operate before you verify each measurement.

• Always let the source signal settle before taking a reading.

WARNING Observe the following safety precautions when performing these tests:

• Some of the procedures in this section may expose you to dangerous voltages. Use standard safety precautions when such dangerous voltages are encountered to avoid personal injury or death caused by electric shock.

• The maximum common-mode voltage (voltage between any plug-in module terminal and chassis ground) is 300V DC or 300V RMS. Exceeding this value may cause a breakdown in insulation, creating a shock hazard.

Veriﬁcation limits

The veriﬁcation limits stated in this section have been calculated using only the Model 27xx one-year accuracy speciﬁcations, and they do not include test equipment uncertainty. If a particular measurement falls slightly outside the allowable range, recalculate new limits based on both Model 27xx speciﬁcations and pertinent calibration equipment speciﬁcations.

Example reading limit calculation

The following is an example of how reading limits have been calculated. Assume you are testing the 10V DC range using a 10V input value. Using the Model 27xx one-year accuracy speciﬁcation for 10V DC of ± (30ppm of reading + 5ppm of range), the calculated limits are:

Reading limits = 10V ± [(10V × 30ppm) + (10V × 5ppm)] Reading limits = 10V ± (0.0003 + 0.00005) Reading limits = 10V ± 0.00035V Reading limits = 9.99965V to 10.00035V

Calculating resistance reading limits

Resistance reading limits must be recalculated based on the actual calibration resistance values supplied by the equipment manufacturer. Calculations are performed in the same manner as shown in the preceding example, except, of course, that you should use the actual calibration resistance values instead of the nominal values when performing your calculations.

For example, assume that you are testing the 10k Ω range using an actual 10.03k Ω calibration resistance value. Using Model 27xx one-year 10k Ω range accuracy of ± (100ppm of reading + 6ppm of range), the calculated reading limits are:

Ω

Reading limits = 10.03k Ω ± [(10.03k Ω × 100ppm) + (10k Ω × 6ppm)] Reading limits = 10.02894k Ω to 10.03106k Ω

Recommended test equipment

Table 2 summarizes recommended veriﬁcation equipment. You can use alternate equipment as long as that equipment has

speciﬁcations at least as good as those listed in Table 2. Keep in mind, however, that calibrator uncertainty will add to the uncertainty of each measurement.

Table 2

Recommended veriﬁcation equipment

Fluke 5700A Calibrator:

DC voltage AC voltage (1kHz, 50kHz) Resistance

100mV:±14ppm

1.0V:±7ppm 10V:±5ppm 100V:±7ppm 1000V:±9ppm

Fluke 5725A Ampliﬁer:

AC Voltage, 50kHz: 700V, ±375ppm

Keithley 3930A or 3940 Frequency Synthesizer:

1V RMS, 10V RMS, 1kHz, ±5ppm, steady state and burst modulation

General Radio 1433-T Precision Decade Resistance Box:

to 400 Ω , ±0.02%

Miscellaneous Equipment:

Double banana plug to double banana plug shielded cables (2) BNC to double banana plug shielded cable

100mV:±200ppm

1.0V:±82ppm 10V:±82ppm 100V:±90ppm 700V:±85ppm

100 1k 10k 100k 1M 10M 100M

:±17ppm

:±12ppm

:±11ppm

:±13ppm

:±18ppm

:±37ppm

:±120ppm

NOTE: The Fluke 5725A ampliﬁer is necessary only if you wish to verify the 750V AC range at 50kHz. Veriﬁcation at

220V and 50kHz using only the 5700A calibrator is adequate for most applications.

Performance veriﬁcation procedures

H L

CH1

H L CH2

NOTE

The following procedures check one channel (CH1) or one channel pair (CH1 and CH21) of the Model 7708 card. To check other channels (or channel pairs), modify the procedures by connecting the veriﬁcation equipment to the appropriate channel (or channel pair) and then closing that channel.

Verifying DC voltage

Check DC voltage accuracy by applying accurate voltages from the DC voltage calibrator to the Model 7708 input terminals and verifying that the displayed readings fall within speciﬁed limits.

CAUTION

Follow these steps to verify DC voltage accuracy:

1. Connect the Model 7708 CH1 H and L INPUT terminals to the DC voltage calibrator as shown in Figure 9.

NOTE

Figure 9

Connections for DC volts veriﬁcation

Do not exceed 300V DC between plug-in module INPUT H and L terminals or between any adjacent channels.

Use shielded, low-thermal connections when testing the 100mV and 1V ranges to avoid errors caused by noise or thermal effects. Connect the shield to the calibrator’s output LO terminal.

Calibrator (Output DC Voltage)

Output

CH1

Note: Use shielded, low-thermal cables for 100mV and 1V ranges.

H L

CH12

CH38

H L

CH32

H L

CH13

CH39

H L

CH33 H L

H L

CH14

CH40

H L

CH34

H L

SENSE

INPUT

CH15

H L

CH21

H L

H L CH1

CH16

H L

CH22

H L

H L CH2

CH17

H L

CH23

H L

H L CH3

CH18

H L

CH24

H L

CH4

CH6

CH5

CH20

CH19

H L

CH25

CH26

H L

CH27

H L

H L CH9

CH35

H L

CH29

H L

CH10

CH36

H L

CH30

H L

CH11

CH37

H L

CH31

H L

CH7

CH8

CH28

H L

Model 7708

2. Install the Model 7708 in Slot 1 of the Model 27xx, turn on the power, and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

3. Select the DC volts function by pressing the DCV key, and set the Model 27xx to the 100mV range. Close Channel 1 by pressing the CLOSE key and then keying in 101.

4. Set the calibrator output to 0.00000mV DC, and allow the reading to settle.

5. Enable the Model 27xx REL mode. Leave REL enabled for the remainder of the DC volts veriﬁcation tests.

6. Source positive and negative and full-scale voltages for each of the ranges listed in Table 3. For each voltage setting, be sure that the reading is within stated limits.

7. Press the OPEN key to open Channel 1.

Table 3

DCV reading limits

Range Applied DC voltage* Reading limits (1 year, 18° to 28°C)

100mV 1V 10V 100V 1000V

*Source positive and negative values for each range.

100.0000mV

1.000000V

10.00000V

100.0000V

300.000V

99.9925 to 100.0075mV

0.999962 to 1.000038V

9.99965 to 10.00035V

99.9946 to 100.0054V

299.976 to 300.024V

Verifying AC voltage

Check AC voltage accuracy by applying accurate AC voltages at speciﬁc frequencies from the AC voltage calibrator to the Model 7708 inputs and verifying that the displayed readings fall within speciﬁed ranges.

CAUTION

Follow these steps to verify AC voltage accuracy:

1. Connect the Model 7708 CH1 H and L INPUT terminals to the AC voltage calibrator as shown in Figure 10.

3. Select the AC volts function by pressing the ACV key. Close Channel 1 by pressing the CLOSE key and then keying in

101.

Do not exceed 300V RMS between plug-in module INPUT H and L terminals or between adjacent channels, or 8 × 107 V•Hz input, because instrument damage may occur.

Figure 10

H L

CH1

H L CH2

Connections for AC volts veriﬁcation

CH1

H L

CH15 H L

CH21

H L

H L CH1

CH16

H L

CH22 H L

H L CH2

CH17 H L

CH23

H L

CH4

CH3

CH18

H L

CH24

H L

CH19 H L

CH25 H L

H L CH5

CH20 H L

CH26

H L

CH6

CH7

CH27

CH28

H L

H L CH8

H L CH9

CH35 H L

CH29 H L

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

CH14

CH40

H L

CH34

H L

Output

H L

SENSE

H L

INPUT

Amplifier (Connect to Calibrator)

Output

Calibrator (Output AC Voltage)

Shielded

Cable

Model 7708

4. Set the Model 27xx for the 100mV range; make sure that REL is disabled.

5. Source 1kHz and 50kHz AC voltages for each of the ranges summarized in Table 4, and make sure that the respective Model 27xx readings fall within stated limits.

6. Press the OPEN key to open Channel 1.

Table 4

ACV reading limits

1kHz reading limits

ACV range Applied AC voltage

100mV 1V 10V 100V 750V

* If the 5725A ampliﬁer is not available, change the 300V @ 50kHz step to 220V @ 50kHz. Reading limits for

220V @ 50kHz = 219.36 to 220.64V.

100.0000mV

1.000000V

10.00000V

100.0000V

300.000V*

(1 year, 18°C to 28°C)

99.910 to 100.090mV

0.99910 to 1.00090V

9.9910 to 10.0090V

99.910 to 100.090V

299.60 to 300.40V

50kHz reading limits (1 year, 18°C to 28°C)

99.830 to 100.170mV

0.99830 to 1.00170V

9.98300 to 10.0170V

99.830 to 100.170V

299.27 to 300.73V

Verifying resistance

H L

CH1

H L

CH2

CH21

H L

CH22

H L

Check resistance by connecting accurate resistance values to the Model 7708 and verifying that its resistance readings are within the speciﬁed limits.

CAUTION Do not apply more than 300V between plug-in module INPUT or SENSE H and L

terminal, or between any adjacent channels, or instrument damage could occur.

Follow these steps to verify resistance accuracy:

1. Using shielded Teﬂon or equivalent cables in a 4-wire conﬁguration, connect the Model 7708 CH1 H and L INPUT terminals, and CH21 H and L SENSE terminals to the calibrator as shown in Figure 11.

3. Set the calibrator for 4-wire resistance with external sense on.

4. Select the Model 27xx 4-wire resistance function by pressing the Ω4 key. Close Channel 1 by pressing the CLOSE key and keying in 101.

Figure 11

Connections for resistance veriﬁcation (100Ω to 10MΩ) ranges)

CH15

H L

CH21 H L

H L CH1

CH1

H L CH2

CH17

CH16

H L

CH22

CH23

H L

CH21

H L CH3

CH18

H L

CH24

H L

H L CH4

CH19

H L

CH25

H L

H L CH5

H L

CH6

CH7

CH20 H L

CH27

CH26

H L

Model 7708

H L CH8

CH28 H L

CH35 H L

CH29

H L

H L CH9

H L CH10

CH36 H L

CH30 H L

H L

CH11

CH37 H L

CH31

H L

CH12

CH38

H L

CH32

H L

CH13

CH39

H L

CH33

H L

H L CH14

CH40

H L

CH34

H L

SENSE

INPUT

Output

Sense

Resistance Calibrator

Sense

Note: Use shielded, low-thermal cables to minimize noise. Enable or disable

calibrator external sense as indicated in procedure.

5. Set the Model 27xx for the 100Ω range, and make sure the FILTER is on. Enable OCOMP (offset-compensated ohms) for the 100Ω range test. (Press SHIFT then OCOMP.)

6. Recalculate reading limits based on actual calibrator resistance values.

7. Source the nominal full-scale resistance values for the 100Ω-10MΩ ranges summarized in Table 5, and verify that the readings are within calculated limits.

Table 5

Limits for resistance veriﬁcation

Nominal

Ω Range

100Ω* 1kΩ 10kΩ 100kΩ 1MΩ 10MΩ 100MΩ

** Enable OCOMP for 100Ω range.

** Calculate limits based on actual calibration resistance values and Model 27xx one-year resistance accuracy

speciﬁcations. See Veriﬁcation limits.

resistance

100Ω 1kΩ 10kΩ 100kΩ 1MΩ 10MΩ 100MΩ

Nominal reading limits (1 year, 18°C to 28°C) Recalculated limits**

99.9880 to 100.0120Ω

0.999894 to 1.000106kΩ

9.99894 to 10.00106kΩ

99.9890 to 100.0110kΩ

0.999890 to 1.000110MΩ

9.99590 to 10.00410MΩ

99.5770 to 100.4230MΩ

__________ to __________ Ω __________ to __________ kΩ __________ to __________ kΩ __________ to __________ kΩ __________ to __________ MΩ __________ to __________ MΩ __________ to __________ MΩ

8. Connect the Model 7708 CH1 and CH21 terminals to the calibrator as shown in Figure 12.

H L

CH1

H L

CH2

CH21

H L

CH22

H L

9. Disable external sense on the calibrator.

10. Set the Model 27xx for the 100MΩ range.

11. Source a nominal 100MΩ resistance value, and verify that the reading is within calculated limits for the 100MΩ range.

12. Press the OPEN key to open Channel 1.

Figure 12

Connections for resistance veriﬁcation (100MΩ range)

CH15

H L

CH21 H L

H L CH1

CH1

H L CH2

CH17

CH16

H L

CH23

CH22

H L

CH21

H L CH3

CH18

H L

CH24

H L

H L CH4

CH19

H L

CH25

H L

H L CH5

H L

CH6

CH7

CH20 H L

CH27

CH26

H L

Model 7708

H L CH8

CH28 H L

CH35 H L

CH29

H L

H L CH9

H L CH10

CH36 H L

CH30 H L

H L

CH11

CH37 H L

CH31

H L

CH12

CH38

H L

CH32

H L

CH13

CH39

H L

CH33

H L

H L CH14

CH40

H L

CH34

H L

SENSE

INPUT

Output

Calibrator (Output 2-Wire Resistance)

Note: Use shielded cables to minimize

noise. Disable calibrator external sense mode.

Verifying temperature

H L

CH1

H L CH2

Thermocouple, thermistor, and RTD temperature readings are derived from DC volts and resistance measurements, respectively. For that reason, it is not necessary to independently verify the accuracy of temperature measurements. As long as the DC volts and resistance functions meet or exceed speciﬁcations, temperature function accuracy is automatically veriﬁed. However, temperature veriﬁcation procedures are provided below for those who wish to separately verify temperature accuracy.

Thermocouple temperature

1. Connect the DC voltage calibrator output terminals and ice point reference to the Model 7708 CH1 H and L INPUT terminals using low-thermal shielded connections, as shown in Figure 13.

3. Select the temperature function by pressing the TEMP key. Close Channel 1 by pressing the CLOSE key and keying in

101.

Figure 13

Connections for thermocouple temperature veriﬁcation

CH1

H L

CH17

H L

CH23

H L

CH6

CH4

CH3

CH5

CH19

CH20

CH18

H L

CH26

CH25

CH24

H L

CH15

CH21

H L

H L CH1

CH16 H L

CH22 H L

H L CH2

Model 7708

Notes: This setup and reading limits

table does not include errors from ice point, thermocouple wire, and connections.

HI and LO connections from the calibrator and Model 7708 must be electrically isolated from each other.

CH27

H L

H L CH7

CH28

H L

H L CH8

H L

CH35

H L

CH29

H L

CH9

CH11

CH10

CH37

CH36

H L

CH31

CH30

H L

Make HI and LO

H L

CH13

CH14

CH12

CH38

CH40

CH39

H L

CH34

CH33

CH32

H L

Twisted

Thermocouple

Connections

in Ice Bath

Wire

H L

Calibrator (Output DC Voltage)

Output

SENSE

INPUT

Output

Low Thermal Copper Connection

Ice Bath

4. Conﬁgure the Model 27xx for °C units, type K temperature sensor, and internal reference junction as follows:

a. Press SHIFT then SENSOR, and note the unit displays the temperature units: UNITS: C. (If necessary, use the cursor

and range keys to select °C units.)

b. Press ENTER. The unit then displays the sensor type: SENS: TCOUPLE.

c. Make sure that TCOUPLE is displayed, then press ENTER. The unit displays the thermocouple type: TYPE: J.

d. Select a type K temperature sensor, then press ENTER. The unit then displays the reference junction type: JUNC: SIM.

e. Select INT reference junction, then press ENTER.

5. Source each of the voltages summarized in Table 6 and verify that the temperature readings are within limits. Be sure to select the appropriate thermocouple type for each group of readings. (See step 3 above.) Open Channel 1 after the test is completed.

Table 6

Thermocouple temperature veriﬁcation reading limits

Thermocouple type Applied DC voltage* Reading limits (1 year, 18°C to 28°C)

*Voltages shown are based on ITS-90 standard.

-7.659mV 0mV

42.280mV

-5.730mV 0mV

54.138mV

-192.33 to -187.67°C

-1.0 to +1.0°C

749.0 to 751.0°C

-192.33 to -187.67°C

-1.0 to +1.0°C

1349.0 to 1351.0°C

RTD temperature

1. Connect the precision decade resistance box (listed in Table 2) to the Model 7708 CH1 and CH21 H and L terminals using four-wire connections. (See Figure 11 for similar connecting scheme.)

3. Select the temperature function by pressing the TEMP key. Close Channel 1 by pressing the CLOSE key and keying in

101.

4. Conﬁgure the Model 27xx temperature function for °C units and RTD temperature sensor (α=0.00385) as follows:

a. Press SHIFT then SENSOR, and note the unit displays the temperature units: UNITS: C.

b. Press ENTER, and note the unit displays the sensor type: SENS: TCOUPLE.

c. Using the cursor and range keys, set the display as follows: SENS: 4W-RTD.

d. Press ENTER, and note the unit displays: TYPE: PT100.

e. Using the cursor and range keys, set the unit for the following display: TYPE: PT385.

f. Press ENTER to complete the temperature conﬁguration process.

5. Set the decade resistance box to each of the values shown in Table 7, and verify that the temperature readings are within the required limits. Open Channel 1when ﬁnished.

Table 7

Plug-in module four-wire RTD temperature veriﬁcation reading limits

Applied resistance* Reading limits (1 year, 18°C to 28°C)

22.80Ω

100.00Ω

313.59Ω

*Based on α = 0.00385. See text.

-190.06 to -189.94°C

-0.06 to +0.06°C

599.94 to 600.06°C

Verifying frequency

H L

CH1

H L

CH2

Follow the steps below to verify the Model 27xx frequency function:

1. Connect the function generator to the Model 7708 CH1 H and L INPUT terminals. (See Figure 14.)

2. Install the Model 7708 in Slot 1 of the Model 27xx, then turn on the power, and allow the unit to warm up for one hour before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

3. Set the function generator to output a 1kHz, 1V RMS sine wave.

4. Select the Model 27xx frequency function by pressing the FREQ key. Close Channel 1 by pressing the CLOSE key and keying in 101.

5. Verify that the Model 27xx frequency reading is between 0.9999kHz and 1.0001kHz.

Figure 14

Connections for frequency veriﬁcation

CH1

CH15

H L

CH21

H L

H L CH1

CH16

H L

CH22

H L

H L CH2

CH17 H L

CH23

H L

H L CH3

CH18

CH24

H L

CH4

CH5

CH19

CH20

H L

CH26

CH25

H L

Model 7708

H L CH6

CH27

H L

H L CH7

CH28

H L

H L CH8

CH35

H L

CH29

H L

H L CH9

H L

CH10

CH36

H L

CH30

H L

H L CH11

CH37

H L

CH31 H L

H L

CH13

CH12

CH38

CH39

H L

CH33

CH32

H L

Coax Cable

H L

CH14

CH40

H L

CH34

H L

50Ω

Function

Output

H L

SENSE

INPUT

Function Generator

Verifying ratio and average

H L

CH1

H L

CH2

CH21

H L

CH22

H L

Follow the procedure below to verify ratio and average.

CAUTION Exceeding 300V between plug-in module INPUT or SENSE H and L terminals may

cause instrument damage.

1. Connect the Model 7708 CH1 and CH21 H and L terminals to the DC calibrator, as shown in Figure 15.

3. Select the Model 27xx DCV function and the 1V range. Close Channel 1 by pressing the CLOSE key and keying in 101.

4. Select the Model 27xx RATIO function (press SHIFT then RATIO).

5. Set the calibrator output to 1.00000V DC, and allow the reading to settle.

6. Verify that the ratio reading is between 0.9999926 and 1.000074.

7. Press OPEN to open Channel 1.

Figure 15

Connections for ratio and average veriﬁcation

CH15

H L

CH21 H L

H L CH1

CH1

H L CH2

CH17

CH16

H L

CH22

CH23

H L

CH21

H L CH3

CH18

H L

CH24

H L

H L CH4

CH19

H L

CH25

H L

H L CH5

H L

CH6

CH7

CH20 H L

CH27

CH26

H L

Model 7708

H L CH8

CH28 H L

CH35 H L

CH29

H L

H L CH9

H L CH10

CH36 H L

CH30 H L

H L

CH11

CH37 H L

CH31

H L

CH12

CH38

H L

CH32

H L

CH13

CH39

H L

CH33

H L

H L CH14

CH40

H L

CH34

H L

SENSE

INPUT

Output

DC Voltage Calibrator

Note: Use shielded cables to minimize

noise.

Calibration

The following procedures calibrate the temperature sensors on the Model 7708 plug-in modules.

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

attempt these procedures unless you are qualiﬁed to do so.

Recommended test equipment

In order to calibrate the Model 7708, you will need equipment summarized in Table 8.

Table 8

Recommended equipment for Model 7708 calibration

Digital Thermometer:

18 to 23°C, ±0.1°C

Keithley 7797 Calibration/Extender Board

Extender board connections

The Model 7708 being calibrated should be connected to the 7797 Calibration/Extender Board, and the extender board should then be installed in scanner Slot #1. Note that the module being calibrated will be external to the Model 27xx to avoid card heating during calibration.

Model 7708 calibration

NOTE Before calibrating the Model 7708, make sure that power has been removed from the card for at

least two hours to allow card circuitry to cool down. After turning on the power during the calibration procedure, complete the procedure as quickly as possible to minimize card heating that could affect calibration accuracy. Allow the Model 27xx to warm up for at least two hours.

Front panel Model 7708 calibration

1. Connect the Model 7708 to the Model 7797 Calibration/Extender Board (see “Extender board connections” above).

2. With the power off, install the Model 7708/7797 combination in Slot 1 and select the rear inputs with the INPUTS switch. Allow three minutes for thermal equilibrium.

3. Accurately measure and record the cold temperature of the Model 7708 card surface at the center of the card with a digital thermometer.

4. Press in and hold the Model 27xx OPEN key while turning on the power.

5. Press SHIFT then TEST, then display TEST:CALIB with the up or down range key. Press ENTER, select RUN, then enter the appropriate calibration code (default: 0027xx).

6. With NEW CODE? displayed, use the up or down range key to display N, then press ENTER.

7. Using the up or down range key, select CARD at the CAL:RUN prompt, then press ENTER.

8. Set the display value to the cold calibration temperature (°C) you measured in Step 3, then press ENTER to complete Model 7708 calibration.

Remote Model 7708 calibration

1. Connect the Model 7708 to the 7797 Calibration/Extender Board (see “Extender board connections” above).

2. With the power off, install the Model 7708/7797 combination in Slot 1, and select the rear inputs with the INPUTS switch. Allow three minutes for thermal equilibrium.

3. Accurately measure and record the cold temperature of the Model 7708 card surface at the center of the card.

4. Press in and hold the Model 27xx OPEN key while turning on the power.

5. Enable calibration by sending the :CODE command. For example, the default command is:

:CAL:PROT:CODE 'KI0027xx'

6. Initiate calibration by sending the following command:

:CAL:PROT:CARD1:INIT

7. Calibrate the Model 7708 with the following command:

:CAL:PROT:CARD1:STEP0 <temp>

Here <temp> is the cold calibration temperature (°C) measured in Step 3.

8. Send the following commands to save calibration and lock out calibration:

:CAL:PROT:CARD1:SAVE :CAL:PROT:CARD1:LOCK

Replaceable parts

This section contains replacement parts information and the component layout drawing for the Model 7708.

Parts list

Replaceable parts for the Model 7708 are listed in Table 9.

Table 9

Model 7708 parts list

Circuit Designation Description Keithley Part No.

C1, C3, C4, C7, C9-C11, C14, C200, C201,

C203-C213

C2, C6, C17-C20, C23-C25, C202 CAP, 47pF, 5%, 100V, CERAMIC C-465-47P

C5 CAP, 4.7µF, 10%, 35V, TANTALUM C-476-4.7

C16 CAP, 220µF, 20%, 10V, TANTALUM C-558-220

CR1-CR14, CR15-CR42, CR45, CR48-CR56 DIODE, DUAL SWITCHING, BAV99L RF-82

CR43, CR44, CR46, CR47 DIODE, SWITCHING, MMBD914 RF-83

CR101-CR104 DIODE, DUAL HIGH SPEED RF-147

J1015 CONN, RT ANGLE DUAL ROM RECEPT CS-1065-1

K1-K41 LATCHING RELAY, SINGLE COIL RL-225

K42, K43 NON-LATCHING RELAY RL-242

Q4, Q6 DIGITAL TRANS, DUAL PNP TG-386

Q5 N-CHANNEL/P-CHANNEL POWER MOSFET TG-360

Q7 DIGITAL TRANS, DUAL PNP TG-385

Q25, Q27, Q29, Q31, Q33, Q35, Q37, Q39,

Q41, Q43, Q45, Q47, Q49, Q51

Q26, Q28, Q30, Q32, Q34, Q36, Q38, Q40,

Q42, Q44, Q46, Q48, Q50, Q52

R1 RES, 69.8kΩ, 1%, 1W, THICK FILM R-418-69.8K

R2, R3, R5, R6, R108-R110, R12 RES, 1kΩ, 1%, 100mW, THICK FILM R-418-1K

R4 RES, 10kΩ, 1%, 100mW, THICK FILM R-418-10K

R7-R13 RES ARRAY, 4 x 4.3kΩ, 5%, 100mW TF-276-4.3K

R14, R55 RES, 137Ω, 1%, 125mW, METAL FILM R-391-137

R200-R202 RES, 470Ω, 5%, 125mW, METAL FILM R-375-470

R203-R205 RES, 4.7kΩ, 5%, 125mW, METAL FILM R-375-4.7K

R206, R207 RES, 1kΩ, 5%, 125mW, METAL FILM R-375-1K

TE1, TE3, TE106, TE112, TE113 CONN, 4-PIN, JOLO BB-125-04 TE-115-4

TE2, TE4, TE101-T3103, TE107-TE109 CONN, 8-PIN TE-115-8

U1-U3, U6, U8 IC, 8-STAGE SHIFT/STORE, MC14094BD IC-772

U7, U25 IC, POS NAND GATES/INV, 74HCT14 IC-656

U9, U10 IC, DUAL OPTO IC-1358

U11, U12 IC, 8-CHAN ANA MULTIPLEXER, DG408DY IC-844

U13, U31-U38 IC, CENTIGRADE TEMP SENSOR, LM35DM IC-906

U14 IC, RETRIG., MULTIVIB, 74HC123AM IC-788

U16 IC, 2.5V, CASCADABLE SERIAL EEPROM LSI-212

U24 IC, QUAD 2 IN AND, 74HCT08 IC-837

CAP, 0.1µF, 20%, 50V, CERAMIC C-418-.1

TRANS, PNP SILICON TG-388

TRANS, NPN SILICON TG-389

TOP COVER HEAT STAKE ASSEMBLY 7700-302A

BOTTOM CARD COVER 7702-301C

COMPRESSION SPRING SP-7-3

Ordering information

To place an order, or to obtain information concerning replacement parts, contact your Keithley representative or the factory (see inside front cover for addresses). When ordering parts, be sure to include the following information:

• Card model number (Model 7708)

• Card serial number

• Part description

• Component designation (if applicable)

• Keithley part number

Factory service

If the instrument is to be returned to Keithley Instruments for repair, perform the following:

• Call the Repair Department at 1-888-KEITHLEY for a Return Material Authorization (RMA) number.

• Complete the service form at the back of this manual, and include it with the instrument.

• Carefully pack the instrument in the original packing carton.

• Write ATTENTION REPAIR DEPARTMENT and the RMA number on the shipping label.

Component layout

The component layout for the Model 7708 is shown at the end of this packing list.

7708 40-Channel Differential Multiplexer w/Automatic CJC

GENERAL

40 CHANNELS: 40 channels of 2-pole relay input. All channels configur-

able to 4-pole.

RELAY TYPE: Latching electromechanical.

ACTUATION TIME: <3ms.

Specified for Model 2700, firmware revision BO2 or later.

CAPABILITIES

CHANNELS 1–40: Multiplex one of 40 2-pole or one of 20 4-pole signals

into DMM. Configuration supports dual 1×20 independent multiplexers.

INPUTS

MAXIMUM SIGNAL LEVEL:

Channels (1–40): 300V DC or rms, 1A switched, 60W, 125VA maximum.

SAFETY: Conforms to European Union Directive 73/23/EEC EN61010-1,

CAT I.

CONTACT LIFE (typ): >10

CONTACT RESISTANCE: <2Ω at end of contact life.

CONTACT POTENTIAL: <±500nV typical per contact, 1µV max.

OFFSET CURRENT: <100pA.

CONNECTOR TYPE: Screw terminal, #20 AWG wire size.

ISOLATION BETWEEN ANY TWO TERMINALS: >10

ISOLATION BETWEEN ANY TERMINAL AND EARTH: >10 CROSS TALK (1MHz, 50ΩLoad): <–40dB. INSERTION LOSS (50ΩSource, 50ΩLoad): <0.35dB below 1MHz.

COMMON MODE VOLTAGE: 300V between any terminal and chassis.

T/C COLD JUNCTION: 1.0°C (18°–28°C Mainframe Temp)

operations at max signal level.

>108operations cold switching.

<±500nV typical per contact pair, 1µV max.

Ω, <200pF.

Ω, <400pF.

<3dB below 2MHz.

1.5°C (0°–18°C & 28°–50°C Mainframe Temp).

Card Input

Card Sense

Cold junction Ref ×4

Channel 1

(Channels 2–19)

Channel 20

Cold junction Ref ×5

Channel 21

(Channels 22–39)

Channel 40

Channel 41

2-Pole (Open)

4-Pole (Closed)

(see Note)

Channel 43

(see Note)

Backplane

isolation

Channel 42

(see Note)

Backplane

isolation

NOTE Channels 41–43 in this schematic

refer to the designations used for control and not actual available channels.

For more information, refer to the ROUTe:MULTiple command section in the Model 2700 User’s Manual.

Channels 42 and 43 can be individually controlled using ROUTe:MULTiple if the module is not to be connected to the internal DMM.

Input

Sense

To Model 2700 Backplane

ENVIRONMENTAL:

OPERATING ENVIRONMENT: Specified for 0°C to 50°C.

Specified to 80% R.H. at 35°C.

STORAGE ENVIRONMENT: –25°C to 65°C.

WEIGHT: 0.52kg (1.16 lb).

Specifications are subject to change without notice.

SBG 11/7/00

Rev. B

Specifications are subject to change without notice.

All Keithley trademarks and trade names are the property of Keithley Instruments, Inc. All other trademarks and trade names are the property of their respective companies.

Keithley Instruments, Inc. 28775 Aurora Road • Cleveland, Ohio 44139 • 440-248-0400 • Fax: 440-248-6168

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

Sales Offices: BELGIUM: Bergensesteenweg 709 • B-1600 Sint-Pieters-Leeuw • 02-363 00 40 • Fax: 02-363 00 64

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Printed in the U.S.A.

5/03

Keithley 7708 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Safety Precautions

Introduction

Calibration

Replaceable parts

7708 40-Channel Differential Multiplexer w/Automatic CJC