Model 2701 User’s Manual Close/Open Switching Module Channels 2-23
Anomaly #2 example — opening the paired channel
Assume 4-wire connections to a 1kΩ resistor using channels 1 and 11 of the Model 7700
switching module. 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. Use the ALL option for the OPEN key (OPEN: ALL) to open all channels in the
mainframe.
Remote programming: ROUT:OPEN:ALL
2. Press the key to close (and display) channel 101. The following channels close
(see Figure 2-2):
• Channel 101 (system channel).
• Channel 125 (connects channel 101 to DMM Input).
• Channel 111 (paired channel for 4-wire measurements).
• Channel 124 (connects channel 111 to DMM Sense).
• Channel 123 (isolates channel 101 from channel 111).
The Model 2701 will display the 1kΩ reading for system channel 101.
Remote programming:
ROUT:CLOS (@101)
3. Using the MULTI option for the OPEN key, open channel 111. This opens the
connection to DMM Sense and causes an OVRFLW reading. Keep in mind that
channel 101 is still closed and displayed as the system channel.
Remote programming: ROUT:MULT:OPEN (@111)
4. In an attempt to clear the overflow reading problem, use the SINGLE option of the
CLOSE key to again close channel 101. You might think that this will again close
channel 111 to reconnect it to DMM Sense. However, that is not the case. Since
channel 101 is still the system channel, selecting it again in this manner is a “no
action”. Channel 111 does not close.
Remote programming: ROUT:CLOS (@101)
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 101. All the listed channels in step 2 will close to make
the 4-wire connection to the 1kΩ resistor.
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