Agilent Technologies 34970A Service Manual page 152

Chapter 5 Theory of Operation
Switch Modules
A single relay is used to switch two input channels. The choice of
which channel is connected to the common is performed by relay K422.
Channels are paired 20 channels apart (Ch 1 with Ch 21, Ch 2 with
Ch 22, etc.) Relay K421 connects the common to the backplane
analog bus for use with the internal DMM.
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