34901A 20-Channel Multiplexer

This module is divided into two banks of 10 channels each. Two additional

fused channels are available for making direct, calibrated dc or ac

current measurements with the internal DMM (external shunts are not
required). All 22 channels switch both HI and LO inputs, thus providing
fully isolated inputs to the internal DMM or an external instrument.

When making 4-wire resistance measurements, the instrument automatically

pairs channel n with channel n+10 to provide the source and sense

connections. The module has a built-in thermocouple reference junction

to minimize errors due to thermal gradients when measuring thermocouples.

Reference
Junction
Sensor
Channel Switches
Shunt Switches
Fuse
Fuse
Bank Switch
Backplane Switches
Internal
DMM Input
Internal
DMM Input
(4W Sense)
Internal
DMM Input
(Current)
21
22
21
22
96
97
98
20
11
Com (4W Sense)
Com
10
01
99
95
Com (Current)
NOTES:
• Only one of channels 21 and 22 can be connected to the internal DMM and/or Com at a time;
connecting one channel will close the other (thus shorting the input “I” to “LO”).
• If any channels are configured to be part of the scan list, you cannot close multiple channels;
closing one channel will open the previously closed channel.
• Connections to ac line are not recommended unless you provide external transient suppression.
Current Channels

Chapter 4 Features and Functions

34901A 20-Channel Multiplexer

164