Keithley 2700, User Manual, Page: 217 / 500

7-4 Scanning Model 2700 Multimeter/Switch System User’s Manual
Scan process
Basic scan — For functions that use 2-wire measurements, the basic scan process is to (1)
open any closed channel, (2) close a channel, and then (3) perform the measurement. This
3-step process is repeated for each channel in the scan. The last scanned channel opens.
Channel pair scan — For the functions that use 4-wire measurements (
Ω
4 and 4-wire
RTD TEMP), the scan process uses paired channels. The scan process is to (1) open any
closed channels, (2) close the paired channels, and then (3) perform the 4-wire measure-
ment. The last scanned channel pair opens.
NOTE For the Model 7700 switching module, primary channels 1 through 10 are
paired to channels 11 through 20. Channel 1 is paired to channel 11, channel 2
is paired to channel 12, channel 3 is paired to channel 13, and so on.
Calculations using channel pairs — Ratio and channel average performs measurements
on two channels and then calculates (and displays) the result. Therefore, these 2-channel
calculations also use paired channels. The scan process is to (1) open any closed channels,
(2) close the primary (displayed) channel and perform a measurement, (3) open the
primary channel, (4) close the paired channel and perform a measurement, (5) calculate
and display the result, and finally (6) open the paired channel.
NOTE When scanning, the displayed channel number (i.e., 101) is not necessarily the
channel that is presently closed:
If both a reading AND a scan channel are displayed, the reading and
annunciators pertain to that channel, but that channel is no longer closed. The
next channel in the scan list is the one that is now closed. Therefore, the reading
(and annunciators) pertain to the channel and does not necessarily indicate the
present state of the Model 2700.
If the display is blanked (-------), the displayed channel is closed and has not
been measured.
Trigger models
NOTE
The following information on trigger model operations apply specifically to
front panel operation.
Block diagrams, known as trigger models, are used to show the two fundamental scan
functions; STEP or SCAN. These two scan functions are enabled by the STEP and SCAN
keys respectively. The trigger models for scanning are shown in
Figure 7-1 and Figure 7-2 .