34908A 40-Channel Single-Ended Multiplexer
The module is divided into two banks of 20 channels each. All of the
40 channels switch HI only, with a common LO for the module.
The module has a built-in thermocouple refe rence junction to minimizeerrors due to thermal gradients when measuring thermocouples.
NOTES:
• Refer to the diagrams on page 20 to connect wiring to the module.
• Only one channel can be closed at a time; closing one channel will open the previously
closed channel.
• This module cannot be used to directly measure current or any 4-wire measurements.
• When connecting thermocouples to the screw terminals on this module (not recommended
due to the common LO configuration), be sure to provide electrical isolation between
thermocouples to avoid current loops and subsequent measurement errors.
• Connections to ac line are not recommended unless you provide external transient suppression.
Maximum Input Voltage: 300 V (CAT I)
Maximum Input Current: 1 A
Maximum Switching Power: 50 W
WARNING: To prevent electrical shock, use only wire that is rated for the highest voltage
applied to any channel. Before removing a module cover, turn off all power to external devices
connected to the module.
Channel Switches
Bank Switch
Backplane
Switch
Internal
DMM Input
Reference
Junction
Sensor
98
40
21
01
99
20
Com
Com
6 mm
20 AWG Typical
Chapter 4 Features and Functions 34908A 40-Channel Single-Ended Multiplexer176