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2-20
Anomaly #2 example — opening the paired channel
Assume 4-wire connections to a 1kΩ resistor using channels 1 and 21 of the 7702 switch-
ing module (in slot 2). Also assume the Ω4 function is selected. The following procedure
demonstrates how careless multiple channel operation can cause an overflow reading even
though everything else from the front panel "looks right."
1.
2.
3.
4.
A simple way to resolve the above problem is to repeat step 1 to open all channels and
then repeat step 2 to close channel 201. All the listed channels in step 2 will close to make
the 4-wire DMM connection to the 1kΩ resistor.
Use the ALL option for the OPEN key (OPEN: ALL) to open all channels in the
mainframe.
Remote programming:
Press the
key to close (and display) channel 201. The following channels close
(see
Figure
2-2):
•
Channel 201 (system channel).
•
Channel 245 (connects channel 201 to DMM Input).
•
Channel 221 (paired channel for 4-wire measurements).
•
Channel 244 (connects channel 221 to DMM Sense).
•
Channel 243 (isolates channel 201 from channel 221).
The Model 2790 will display the 1kΩ reading for system channel 201.
Remote programming:
Using the MULTI option for the OPEN key, open channel 221. This opens the
connection to DMM Sense and causes an OVRFLW reading. Keep in mind that
channel 201 is still closed and displayed as the system channel.
Remote programming:
In an attempt to clear the overflow reading problem, use the SINGLE option of the
CLOSE key to again close channel 201. You might think that this will again close
channel 221 to reconnect it to DMM Sense. However, that is not the case. Since
channel 201 is still the system channel, selecting it again in this manner is a "no
action". Channel 221 does not close.
Remote programming:
Model 2790 SourceMeter
ROUT:OPEN:ALL
ROUT:CLOS (@201)
ROUT:MULT:OPEN (@221)
ROUT:CLOS (@201)
®
Switch System Reference Manual
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