User`s guide

302
Chapter 7 Tutorial
Low-Level Signal Multiplexing and Switching
Four-Wire Multiplexers
You can make 4-wire ohms measurements using the 34901A and 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.
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.
Channel 1 Source
Channel 11 Sense
Channel 12 Sense
To DMM Source
Bank Relay
To DMM Sense
Channel 2 Source
Source
HI
LO
R Sense
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34970A Refresh UG.book Page 302 Wednesday, February 17, 2010 12:34 PM