Keithley 2790, Reference Manual

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Model 2790 SourceMeter
®
Switch System Reference Manual 5-19
Basic operation
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Make sure the INPUTS switch is set to the REAR position (in).
1. Select and configure (range, filter, rel, etc.) a valid measurement function. For
ratio, the only valid function is DCV. For channel average, the only valid functions
are DCV and TEMP (TCs only).
2. Use the or key to select (close) a primary channel (101 through 120 for the
Model 7702). The CLOSE key can also be used.
3. Apply one signal to the selected primary channel and apply the other signal to the
paired channel. For the Model 7702, if the closed primary channel is 101, the
paired channel is 121.
4. Enable Ratio or Channel Average:
• Ratio — Press SHIFT and then RATIO. The RATIO annunciator will turn on
to indicate that the displayed readings are the result of the ratio calculation.
• Channel Average — Press SHIFT and then CHA-AVG. The DELTA annuncia-
tor will turn on to indicate that the displayed readings are the result of the
channel average calculation. To disable channel average, again press SHIFT
and then CH-AVG.
5. When finished, there are two ways to disable the calculation:
• Press the OPEN key. The calculation will disable and the channel will open.
• Press SHIFT and then RATIO to disable ratio or press SHIFT and then
CHA-AVG to disable channel average. The calculation will disable, but the
channel will remain closed.
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The paired channel number is not displayed when it is measured. Only the pri-
mary channel is displayed during the 2-channel scan for the calculation.
Enabling ratio disables channel average and conversely, enabling channel aver-
age disables ratio.
If either of the channel readings over range (“OVRFLW”), the result of the cal-
culation will also be “OVRFLW.”
When using limits with ratio or channel average, the limit values will be com-
pared to the result of the calculation and not to the individual channels.
With ratio or channel average enabled, pressing a function key will display the
“EXIT RATIO” or “EXIT CHAN AVG” message to indicate that the calculation
must first be disabled as explained in step 5 of the above procedure.