Chapter 8 Tutorial

Low-Level Signal Multiplexing and Switching

Four-Wire Multiplexers

You can make 4-wire ohms measurements using the HP 34901A and HP 34902A multiplexers. For a 4-wire ohms measurement, the channels are divided into two independent banks by opening the bank relay.

For 4-wire measurements, the instrument automatically pairs channel n with channel n+10 (34901A) or n+8 (34902A) to provide the source and sense connections. For example, make the source connections to the HI and LO terminals on channel 2 and the sense connections to the HI and LO terminals on channel 12.

To DMM Source

Channel 1 Source

Bank Relay

Channel 2 Source

To DMM Sense

Channel 11 Sense

 

Channel 12 Sense

Note: 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.

When making a 4-wire measurement, the test current flows through the source connections from the HI terminal through the resistor being measured. To eliminate the test lead resistance, a separate set of sense connections are used as shown below.

HI +

Source

R Sense

LO

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