Tektronix 7708 User manual

Keithley Instruments

28775 Aurora Road
Cleveland, Ohio 44139
1-800-935-5595

tek.com/keithley

Model 7708 Multiplexer Module

Instructions for use with DAQ6510

077144500 / April 2018 *P077144500* 1

Introduction

The Model 7708 40-Channel Differential Multiplexer Plug-In Module with Automatic CJC offers 40 channels
of 2-pole or 20 channels of 4-pole multiplexer switching that can be configured as two independent banks
of multiplexers. Automatic CJC is provided so that no other accessories are required to make thermocouple
measurements. The 7708 is ideal for RTD, thermistor, and thermocouple temperature applications. It is also
well suited for mixed-signal measurement applications that require multi-point monitoring, such as
environmental stress screening.

Figure 1: Model 7708 40-Channel Differential Multiplexer Module

Item shipped may vary from model pictured here.

Model 7708 Multiplexer Module Instructions for use with DAQ6510

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The 7708 includes the following features:

▪ DC and AC voltage measurement
▪ Two-wire or four-wire resistance measurements (automatically pairs switches for four-wire

measurements—n + 20)

▪ Temperature applications (RTD, thermistor, thermocouple)
▪ Built-in cold junction reference
▪ Screw terminal connections

The 7708 can be used with the DAQ6510 data acquisition instrument.

If you are using this switching module with the 2700, 2701, or 2750, please see the Model 7708 40­Channel Differential Multiplexer with Automatic CJC User's Guide, Keithley Instruments document
number PA-744.

Connections

Connection and wiring procedures in this document are intended for use by qualified
personnel only. Do not perform these procedures unless qualified to do so. Failure to
recognize and observe normal safety precautions could result in personal injury or death.

Do not exceed the maximum specifications for the 7708 module. Refer to the specifications
provided in the data sheet. Failure to recognize and observe normal safety precautions could
result in personal injury or death.

Model 7708 Multiplexer Module Instructions for use with DAQ6510

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Wiring procedure

Use the following procedure to make connections to the 7708 module. Make all connections using the correct
wire size (up to 20 AWG).

All wiring must be rated for the maximum voltage in the system. For example, if 1000 V is
applied to the front terminals of the instrument, the switching module wiring must be rated
for 1000 V. Failure to recognize and observe normal safety precautions could result in
personal injury or death.

Equipment needed:

▪ Flat-blade screwdriver
▪ Cable ties

To wire the 7708 module:

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

2. Using a screwdriver, turn the access screw to unlock and open the cover.

Figure 2: Screw terminal access

3. Using a small flat-blade screwdriver, loosen terminal screws and install wires as needed. Channel
designations for the screw terminals are shown in the following figure.

Model 7708 Multiplexer Module Instructions for use with DAQ6510

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4. Route wire along the cable path and secure with cable ties as shown. The following figure shows
connections to channels 1 and 2.

Figure 3: Wire dressing

5. Record the connections in the Connection log (on page 8).

6. Close the cover.

7. Using a screwdriver, press in the access screw and turn to lock the cover.

Model 7708 Multiplexer Module Instructions for use with DAQ6510

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Schematic diagram

The simplified schematic diagram of the 7708 is shown in the following figure. The channels are grouped into
two banks of 20 channels (40 channels total). Backplane isolation is provided for each bank. Each bank also
includes separate cold junction reference points.

The first bank contains channels 1 to 20 and the second bank contains channels 21 to 40. Each channel is
wired with separate inputs for HI/LO, providing fully isolated inputs.

Although the 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 reset command is issued.

Connections to DMM functions are provided through the module backplane connector of the instrument.
When automatically configured for 4-wire measurements (including 4-wire resistance and RTD temperature),

the channels are paired as shown in the following table. Connect 4-wire sense leads using channels 21 to 40.

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

The 7708 switching module has 40 channels that can calculate ratio and channel average. The ratio calculation
can be done for the DCV function, and the channel average calculation can be done for the DCV and TEMP
(thermocouples only) functions. Paired channels are used for ratio and channel average. Channels are paired
in the same manner as they are for 4-wire measurements.

Model 7708 Multiplexer Module Instructions for use with DAQ6510

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Figure 4: Model 7708 simplified schematic

Channel 41 (2W/4W Configuration), Channel 42 (Sense Isolation), and Channel 43 (Input Isolation) are
normally automatically configured by the DAQ6510.

Model 7708 Multiplexer Module Instructions for use with DAQ6510

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Typical connections

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

▪ Thermocouple
▪ Two-wire resistance and thermistor
▪ Four-wire resistance and RTD
▪ DC or AC voltage

Thermocouple connections

Figure 5: Thermocouple connections

Two-wire resistance and thermistor connections

Figure 6: Two-wire resistance and thermistor connections

Model 7708 Multiplexer Module Instructions for use with DAQ6510

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Four-wire resistance and RTD connections

Figure 7: 4-wire resistance and RTD connections

DC or AC voltage connections

Figure 8: Voltage connections - DC or AC

Model 7708 Multiplexer Module Instructions for use with DAQ6510

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Connection log

You can use the next table to record your connection information.

Channel

Color

Description

Description

Color

Channel

INPUT
H

L

SENSE
H

L

CH1
H

H

CH21
L

L

CH2
H

H

CH22
L

L

CH3
H

H

CH23
L

L

CH4
H

H

CH24
L

L

CH5
H

H

CH25
L

L

CH6
H

H

CH26
L

L

CH7
H

H

CH27
L

L

CH8
H

H

CH28
L

L

CH9
H

H

CH29
L

L

CH10
H

H

CH30
L

L

CH11
H

H

CH31
L

L

CH12
H

H

CH32
L

L

CH13
H

H

CH33
L

L

CH14
H

H

CH34
L

L

CH15
H

H

CH35
L

L

CH16
H

H

CH36
L

L

CH17
H

H

CH37
L

L

CH18
H

H

CH38
L

L

CH19
H

H

CH39
L

L

CH20
H

H

CH40
L

L