Keithley 2700, User Manual, Page: 189 / 500

5-16 Rel, Math, Ratio, Channel Average, dB Model 2700 Multimeter/Switch System User’s Manual
Ratio and channel average
With a switching module installed in the Model 2700, the ratio or average of two channels
can be calculated and displayed. The ratio calculation can be done on the DCV function,
and the channel average calculation can be done on the DCV and TEMP (thermocouples
only) functions.
Ratio and channel average are calculated as follows:
where: Chan A is the selected (closed) channel.
Chan B is the paired channel for the installed switching module.
Ratio and Channel Average is the displayed result of the respective calculation.
Paired channels are used for ratio and channel average. For example, the Model 7700
switching module has 20 channels that can use ratio and channel average. The primary
channels (1 through 10) are linked to the paired channels (11 through 20). Channel 1 is
paired to channel 11, channel 2 is paired to channel 12, and so on.
When ratio or channel average is enabled, the Model 2700 measures the closed primary
channel. It then opens the primary channel and closes and measures the paired channel.
Ratio or channel average is then calculated from the two readings and displayed. If the
Model 2700 is configured for continuous measurements, the two-channel scan will
continue to repeat and refresh the display with each new calculated reading.
The ratio or channel average calculation can only be enabled if a valid switching channel
is closed. If no channel is closed when you attempt to enable one of these calculations, the
message “CLOSE A CHAN” message will be displayed to remind you to first close a
valid channel.
A primary channel must be closed before you can enable ratio or channel average. If a
paired channel is instead closed, message “INVALID CHAN” will be displayed to
indicate the settings conflict.
NOTE
The various instrument operations, including Ratio or Channel Average, are
performed on the input signal in a sequential manner. See
“Signal processing
sequence,” page D-2 , for details. It includes a flowchart showing where in the
processing sequence that Ratio or Ch Avg operation is performed.
Ratio
Chan A
Chan B
------------------ =
Channel Average
Chan A Chan B +
2
------------------------------------------- =