Channel Assignments; Sequential And Non-Sequential Scans; Scan Process - Keithley 2750 User Manual

Model 2750 Multimeter/Switch System User's Manual

Channel assignments

A switching module has a certain number of channels. For example, the Model 7700
switching module has 22 channels (1 through 22). When you encounter a 1 or 2-digit
channel number in this manual, the switching module channel is the point of discussion.
A switching module can be installed in one of five slots of the mainframe. Therefore, to
close/open or scan a channel, it is necessary to specify the slot location and channel num-
ber of the switching module. This is accomplished by using a 3-digit channel number for
the mainframe. The first digit (1, 2, 3, 4 or 5) indicates the slot number, and the next two
digits indicate the channel number of the switching module. Examples:
Channel 101
Channel 112
Channel 320

Sequential and non-sequential scans

Only a sequential scan can be configured from the front panel. For a sequential scan, the
scan proceeds from the lowest numbered channel to the highest. For example, assume
channels 101, 102, 105, 108 and 109 are selected for a scan. The scan will run in this
order: 101 > 102 > 105 > 108 > 109.
For remote programming, a non-sequential scan can be configured. Channels are scanned
in the order that they are listed in the scan list. This allows backward scanning. For exam-
ple, assume the following scan list:
(@101, 102, 104, 105, 103, 109)
The above scan will run in this order: 101 > 102 > 104 > 105 > 103 >109. Notice that after
channel 105 is scanned, the unit backs up to scan channel 103. It then proceeds forward to
scan channel 109. Any scan that performs backward scanning is considered a non-sequen-
tial scan. For more information on non-sequential scanning, see the reference information
for the ROUT:SCAN command that follows
NOTE

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 (Ω4 and 4-wire
RTD TEMP), the scan process uses paired channels. The scan process is to (1) open any
Slot 1, channel 1
Slot 1, channel 12
Slot 3, channel 20
Non-sequential scanning is only intended to be performed using remote pro-
gramming. Unexpected results may occur if a non-sequential scan is run from
the front panel.
Table 7-1.
Scanning 7-3