Keithley 2790, Reference Manual

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2-14 Model 2790 SourceMeter
®
Switch System Reference 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 2790. 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.
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Use the VIEW option of the CARD menu to display closed channels (see
“CARD menu,” page 2-26 ).
Controlling multiple channels
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When using multiple channel operation, you must be very careful
when switching external hazardous voltages. If you inadvertently close
the wrong channel(s), you could create a shock hazard and/or cause
damage to the equipment.
Switching modules use latching relays. That is, closed channels remain
closed when the Model 2790 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 connections to the
module, and (2) installing (or removing) the module into (or out of) the
Model 2790.
Avoiding corrupt measurements
Aside from the safety issues, improper use of multiple channel operation can result in cor-
rupt measurements. For example, assume a 7751 installed in slot 1 and a 7702 installed in
slot 2. If you use multiple channel operation to close channels 101, 114, and 118, you will
connect the DUT at channel 1 of the 7751 to the DMM for measurement.
If you then use system channel operation to close channel 201, the input at channel 201 will
connect to the DMM. You now have the DUT at channel 1 of the 7751 and the input on
channel 201 of the 7702 connected to DMM Input at the same time, inviting all sorts of prob-
lems.
The above problem can be avoided by opening all channels before closing channel 201 as
demonstrated by the following sequence:
1. Multiple channel operation — Close channels 101, 114, and 118 for 7751 connec-
tion to DMM.
2. Open all channels to disconnect modules from DMM.
3. System channel operation — Close system channel 201 for 7702 to connect to DMM.