User`s guide

213

Chapter 4 Features and Functions

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 reference junction to minimize errors due to

thermal gradients when measuring thermocouples.

NOTES:

• Refer to the diagrams on page 27 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

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.

Bank Switch

Channel Switches

Backplane

Internal

DMM Input

Reference

Junction

Sensor

Com

Switch

Com

6mm

20 AWG Typical

34970A Refresh UG.book Page 213 Wednesday, February 17, 2010 12:34 PM