Tektronix KEITHLEY 7700 User manual

Keithley Instruments
28775 Aurora Road
Cleveland, Ohio 44139
1-800-833-9200
tek.com/keithley
Model 7700 Multiplexer Module
Instructions for use with 2750
077182400 July 2023
*P077182400*
1
Introduction
The 7700 20-Channel Differential Multiplexer Plug-In Module offers 20 channels of 2-pole or 10 channels of
4-pole multiplexer switching that can be configured as two independent banks of multiplexers. There are two
additional protected channels for current measurements. Automatic cold junction compensation (CJC) is
provided so that no other accessories are required to make thermocouple temperature measurements. In
addition, the 7700 contains latching electromechanical relays that enable signal bandwidths of up to 50 MHz. The
7700 is ideal for RTD, thermistor, and thermocouple temperature applications.
Figure 1: 7700 20-Channel Differential Multiplexer Module
Item shipped may vary from model pictured here.
The 7700 includes the following features:
2-wire or 4-wire resistance measurements (automatically pairs switches for 4-wire measurements — n + 10)
Screw terminal connections
Built-in cold junction reference
Latching type relays (relays hold their position after power is removed)
Two protected channels for current measurements (external shunts not required)
The 7700 can be used with the DAQ6510 Data Acquisition and Multimeter System and the 2750
Multimeter/Switch System. If you are using the 7700 with a DAQ6510, refer to Model 7700 Multiplexer Module
Instructions for use with DAQ6510, document number 0771443xx.

Model 7700 Multiplexer Module Instructions for use with 2750
2 077182400 July 2023
Switching module capabilities
Channels 1 through 20: The 7700 can multiplex one of 20 2-pole signals, or one of 10 4-pole signals into the
input of the 2750.
Channels 21 and 22: The 7700 can multiplex one of two 2-pole current signals into the input of the 2750.
When you use system channel operation, only one channel or channel pair can be closed at the same
time. When you close a channel or channel pair, all other measurement channels open. The user has
no control of channels 23, 24, and 25. The open and close states of these channels are determined by
the selected function.
The 7700 has six temperature transducers to monitor the cold junction temperature at the screw terminals. For
temperature measurements, this internal reference junction allows thermocouples to be connected directly to the
screw terminals of the module.
When the 2750 is on the DCV, ACV, Ω2, CONT, Ω4, FREQ, PERIOD, or TEMP function, channels 1 through 20
are available. When on a current function (DCI or ACI), channels 21 and 22 are the only available channels.
The 7700 can accommodate 4-wire measurements by using channel pairs. Primary channels 1 through 10
become paired to channels 11 through 20. For example, with the Ω4 function selected, channel 1 becomes paired
to channel 11. For example, when you close channel 1, channel 11 will also close.
The 2-wire functions include DCV, ACV, DCI, ACI, Ω2, CONT, FREQ, PERIOD, and TEMP (thermocouple and
thermistor). The 4-wire functions/operations include Ω4, TEMP (4-wire RTD), RATIO, and CH AVG.
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 CH11
CH6 and CH16
CH2 and CH12
CH7 and CH17
CH3 and CH13
CH8 and CH18
CH4 and CH14
CH9 and CH19
CH5 and CH15
CH10 and CH20

Model 7700 Multiplexer Module Instructions for use with 2750
077182400 July 2023 3
Schematic
The simplified schematic of the 7700 is shown in the following figure.
Figure 2: 7700 simplified schematic

Model 7700 Multiplexer Module Instructions for use with 2750
4 077182400 July 2023
Channels 1 through 20 are used for all measurements except current. Channels 21 and 22 are used for
current only.
There are two backplane relays (channels 24 and 25) that connect the input channels to the backplane of the
instrument. With a 2-wire function (except current) selected, channel 25 closes. With a 4-wire function selected,
both channels 24 and 25 close.
There is a 2-pole/4-pole relay (channel 23) between channels 1 to 10 and channels 11 to 20. When a 2-wire
function (such as DCV) is selected, channel 23 opens (2-pole position) to allow any of the 20 channels to be
connected to the input backplane.
When a 4-wire function is selected, channel 23 closes (4-pole position) to isolate channels 1 through 10 from
channels 11 through 20. When one of channels 1 to 10 is closed, its paired channel (11 through 20) also closes to
connect the sense channel to the sense backplane.
For the two current channels (21 and 22), signal HI and LO are routed directly to the backplane when the channel
is closed.
The Input and Sense screw terminals are connected to the inputs of channels 24 and 25 (backplane isolation
relays). The AMPS screw terminal is connected directly to the instrument.
Channels 23, 24, and 25 in this schematic refer to designations used for control and not actual
available channels. For more information, refer to the instrument reference manual. Also, AMPS and
LO can be connected to another instrument, but you cannot control them through the front panel or by
using remote communications.
If channels 1 through 20 are not connected to the internal DMM, channels 24 and 25 can be controlled
independently using multiple channel operation. Refer to the Model 2750 Multimeter/Switch System User's
Manual, part number 2750-900-01, for more information on multiple channel operation.
Connections
Connection and wiring procedures in this document are intended for use by qualified
personnel only, as described by the types of product users in the Safety precautions (on page
13). 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.

Model 7700 Multiplexer Module Instructions for use with 2750
077182400 July 2023 5
To prevent electric shock that could result in serious injury or death, comply with these safety
precautions:
Before making or breaking any connections to the switching card, make sure the
instrument is turned off and power is removed from all external circuitry.
Do not connect signals that will exceed the maximum specifications of any installed
switching card.
Dangerous arcs of an explosive nature in a high-energy circuit can cause severe personal
injury or death if contacted. If the instrument is connected to a high-energy circuit when set to
a current range, low-resistance range, or any other low-impedance range, the circuit is
virtually shorted. Dangerous arcing can result even when the multimeter is set to a voltage
range if the minimum voltage spacing is reduced in the external connections. For details about
how to safely make high-energy measurements, see “High-energy circuit safety precautions”
in the Reference Manual for the instrument.
Do not exceed the maximum specifications for the 7700. Refer to the specifications provided in
the datasheet. Failure to recognize and observe normal safety precautions could result in
personal injury or death.
The following information describes how to make connections to the switching module and define the channel
designations. A connection log is provided that you can use to record your connections. See Connection log
(on page 10).
This section describes how to make connections to the terminal screws in the module. You can make:
Current connections, provided through two protected channels (channels 21 and 22)
INPUT connections
SENSE (4-wire resistance) connections
AMP and LO common connections to the instrument
Channel 23 (2W/4W Configuration), Channel 24 (Sense Isolation), and Channel 25 (Input Isolation) are normally
automatically configured by the 2750 for system channel operation. However, by using multiple channel
operation, channels can be individually controlled.
Connect 4-wire sense leads using channels 11 to 20. To disconnect channels 11 to 20 from channels
1 to 10, send:
ROUT:MULT:CLOS (@123)
Note opposite logic.

Model 7700 Multiplexer Module Instructions for use with 2750
6 077182400 July 2023
Wiring procedure
Use the following procedure to wire the 7700 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:
Small flat-blade screwdriver
Cable ties
To make connections to the 7700 module:
1. Make sure all power is discharged from the 7700 module.
2. Use a screwdriver to turn the access screw to unlock and open the cover.
Figure 3: Screw terminal access

Model 7700 Multiplexer Module Instructions for use with 2750
077182400 July 2023 7
3. Use a small flat-blade screwdriver to loosen the terminal screws and install the wires as needed.
Figure 4: 7700 screw terminal channel designations

Model 7700 Multiplexer Module Instructions for use with 2750
8 077182400 July 2023
4. Route wire along the wire path and secure with cable tie as shown in the following figure. Make sure to add
supplementary insulation around the harness for voltages above 42 VPEAK. The following figure also shows
connections to channels 1 and 2.
Figure 5: Model 7700 wire dressing
5. Record the connections in the Connection log (on page 10).
6. Close the cover.
7. Use a screwdriver to press in the access screw and turn to lock the cover.
Typical wiring 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
DC or AC current

Model 7700 Multiplexer Module Instructions for use with 2750
077182400 July 2023 9
Figure 6: Thermocouple connections
Figure 7: Two-wire resistance and thermistor connections
Figure 8: Four-wire resistance and RTD connections

Model 7700 Multiplexer Module Instructions for use with 2750
10 077182400 July 2023
Figure 9: DC or AC voltage connections
Figure 10: AC or DC current connections
Connection log
You can use the following table to record your connection information.