Theory of Operation 5
Keysight 34970A/34972A Service Guide 161
The row latch, U102, and column latches, U103 and U104, control the relays. The
row drivers are divided into four groups of set and reset drivers. Each group of row
drivers controls five relays. The column drivers operate as a pair. There are ten
column drivers each controlling two relays. The analog bus backplane relays are
non-latching.
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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