Agilent Technologies Switch/Measure User Manual page 134

4
Low Frequency Multiplexer Switch Modules
This module is interlock protected, which means whenever the D- sub
connector end of the modules is exposed, the Analog Bus relays
immediately open and disconnect from the Analog Bus. For more
information, refer to
Lifetime of relays is severely degraded as current or voltage goes up.
If higher voltage is being switched, limits on source current are
recommended.
When the power is off, all channel and Analog Bus relays open.
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34980A User's Guide