Keithley 7708 40-Channel Multiplexer Module
Description
The 7708 is a plug-in module designed for advanced measurement applications. It features a configurable multiplexer system that offers either 40 channels with 2-pole switching or 20 channels with 4-pole switching, arranged as two independent multiplexer banks. A key feature is its built-in Cold Junction Compensation (CJC) sensors, which automatically linearize thermocouples, making it exceptionally suitable for temperature measurements using RTDs, thermistors, and thermocouples.
Beyond temperature applications, the 7708 excels in mixed-signal measurement scenarios requiring multi-point monitoring, such as environmental stress screening.
The 7708's capabilities include:
- 40 differential channels for diverse measurement needs
- Flexibility to perform both two-wire and four-wire measurements
- Robust capacity of 300 V and 1 A for voltage channels, with 60 W or 125 VA power handling
- User-friendly oversized screw terminal blocks for easier connections
- On-board memory for storing relay closure states
Model Overview
| Capabilities | Channels 1-40: Multiplex one of 40 2-pole or one of 20 4-pole signals into DMM |
|---|---|
| Maximum Signal Level Channels (1-40) | 300 V DC or rms, 1 A switched, 60 W, 125 VA maximum |
| Contact Life (typ.) | >105 operations at max. signal level >108 operations no load (Open thermocouple detector on during thermocouple measurements. Minimum signal level 10 mV, 10 μA) |
|---|---|
| Contact Resistance | <2 Ω at end of contact life |
| Contact Potential | <±500 nV typical per contact, 1 µV max <±500 nV typical per contact pair, 1 µV max |
| Offset Current | <100 pA |
| Connector Type | Screw terminal, #20 AWG wire size |
| Isolation Between Any Two Terminals | >109 Ω, <200 pF |
| Isolation Between Any Terminal and Earth | >109 Ω, <400 pF |
| Cross Talk (1 MHz, 50 Ω Load) | <-40 dB |
| Insertion Loss (50 Ω Source, 50 Ω Load) | <0.1 dB below 1 MHz <3dB below 2 MHz |
| Common Mode Voltage | 300 V between any terminal and chassis |
