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Chapter 4 Features and Functions
System-Related Operations
Relay Cycle Count
The instrument has a Relay Maintenance System to help you predict
relay end-of-life. The instrument counts the cycles on each relay in the
instrument and stores the total count in non-volatile memory on each
switch module. You can use this feature on any of the relay modules and
the internal DMM .
In addition to the channel relays, you can also query the count on
backplane relays and bank relays. Note that you cannot control the
state of these relays from the front panel but you can query the count.
For more information on channel numbering and layout, refer to
"Module Overview" starting on page 163.
You can also query the state of the three relays on the internal DMM .
These relays are numbered "1", "2", and "3". These relays open or
close when a function or range is changed on a module.
The HP 34908A multiplexer contains 40 channels which are switched
( HI only) using only 20 relays. Each relay is used to switch HI on two
different channels (and only one channel can be closed at a time).
The channels are arranged such that channels 01 and 21 use different
contacts on the same relay. The remaining channels are also paired in
the same manner (channels 02 and 22, channels 03 and 23, etc.).
Therefore, when you query the relay count on a channel, the number
reflects the number of times that the relay was closed. For example, the
relay count will always be the same on channels 01 and 21.
You can reset the count (allowed only from remote) but the instrument
must be unsecured (see "Calibration Overview" on page 155 to
unsecure the instrument).
For more information on relay life and load considerations, refer to
"Relay Life and Preventative Maintenance" starting on page 399.
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