2-16 Close/Open Switching Module Channels Model 2750 Multimeter/Switch System User’s Manual
Some other key points for multiple channel operation include the following:
• Closing a channel using multiple channel operation has no affect on other closed
channels. Whatever channels were previously closed, remain closed.
• A channel closed using multiple channel operation is not displayed on the Model
2750. Also, the CHAN annunciator does not turn on when a channel is closed.
• Opening a channel using multiple channel operation has no affect on other closed
channels. Only the specified channel opens.
NOTE Use the VIEW option of the CARD menu to display closed channels (see “CARD
menu,” page 2-28).
Controlling multiple channels
WARNING When using multiple channel operation, you must be very careful
when switching hazardous voltages. If you inadvertently close the
wrong channel(s), you could create a shock hazard and/or cause dam-
age to the equipment.
Most switching modules use latching relays. That is, closed channels
remain closed when the Model 2750 is turned off. Never handle a
switching module that is connected to an external source that is turned
on. Turn off all power sources before (1) making or breaking connec-
tions to the module, and (2) installing (or removing) the module into
(or out of) the Model 2750.
Avoiding corrupt measurements
Aside from the safety issues, improper use of multiple channel operation can result in cor-
rupt measurements. For example, assume two Model 7700s installed in slots 1 and 2, and a
2-wire function selected. If you use multiple channel operation to close channels 201 and
225, you will connect the input at channel 201 to the DMM for measurement.
If you then use system channel operation to close channel 101, channel 125 will also close
to connect the input at channel 101 to the DMM. You now have two input channels (101
and 201) connected to DMM Input at the same time, inviting all sorts of problems.
The above problem can be avoided by opening channels 201 and/or 225 before closing
channel 101 (and 125) as demonstrated by the following sequence:
1. Multiple channel operation — Close channels 201 and 225 for connection to
DMM.
2. Multiple channel operation — Open channels 201 and/or 225 to disconnect from
DMM.
3. System channel operation — Close system channel 101 to connect to DMM.
2750-900-01.book Page 16 Wednesday, August 3, 2011 7:56 AM
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