Agilent Technologies 34970A Service Manual page 145

Chapter 5 Theory of Operation
Switch Modules
The 20 channels are divided into two banks. The banks are combined
by closing K422 for voltage and 2-wire Ohms switching. When K422
is open, the banks are electrically independent of each other and this
configuration is used for 4-wire Ohms multiplexing where the Ohms
current sources are connected to channels 1 through 10 and the sense
is obtained from channels 11 through 20. K421 and K423 control the
connection to the analog bus for measurements using the Internal DMM.
The current measurement channels are selected by relay K522.
Relays K523 and K524 short the inputs when a channel is not
selected. Relay K521 makes the connection to the analog bus for
measurement by the Internal DMM.
K422
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