HP 34970A manual HP 34901A 20-Channel Multiplexer

Chapter 4 Features and Functions

HP 34901A 20-Channel Multiplexer

HP 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 with channel 7 to provide the source and sense connections. The module has a built-in isothermal block to minimize errors due to thermal gradients when measuring thermocouples.

Internal DMM Input

Reference

Junction

Sensor

Internal

DMM Input

(4W Sense)

Internal DMM Input (Current)

NOTES:

Backplane Switches Channel Switches

01

98

10

Com

99Bank Switch

Com (4W Sense)

11

20

97

Shunt Switches

95 21 Fuse

21

Current Channels

96 22 Fuse

22

Com (Current)

∙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.

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