Keithley 2750, Руководство пользователя

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Model 2750 Multimeter/Switch System User’s Manual Scanning 7-9
Delay (Auto or Manual)
— The user can select either auto delay or manual delay. With
auto delay selected, the instrument automatically selects a delay period that will provide
sufficient settling for function and autorange changes, and multi-phase measurements.
The auto delay period cannot be adjusted by the user. It is a fixed delay for the selected
function and range (
Table 8-1 ).
NOTE
When scanning, the auto delay times in Table 8-1 are valid for all control
sources (Immediate, External, Timer, Manual, or Bus).
With manual delay selected, the user can set the delay period from 0 seconds to 99 hours,
99 minutes, 99.999 seconds. However, if you set a delay shorter than the corresponding
auto delay period, measurement uncertainty increases (noisy and/or unsettled readings
may result).
NOTE
Keep in mind that if the timer control source is selected, the Delay period is only
in effect for the first pass through the loop.
Ratio/Chan Average Delay
— With ratio or channel average enabled, a delay is typically
used to keep the channel relays from cycling too fast. The default delay period is 0.5 sec-
onds but can be set from 0 to 999999.999 seconds using remote programming (see
Section 5 for details). Ratio and channel average are covered in Section 5 .
NOTE
The Ratio/Chan Average Delay is in addition to the Timer or Delay (Auto or
Manual). That is, it occurs after the Timer interval or Delay period elapses.
Device action
The channel measurement process is performed at this block. If repeat filter is enabled, the
filter process is also performed.
Reading count
NOTE
For both STEP and SCAN, the reading count specifies the number of readings to
store in the buffer.
STEP operation
— The reading count specifies the number of channels to scan. This can
be equal to, less than, or greater than the number of channels in the scan list. The last
scanned channel remains closed. If you start the scan again, it will start at the next
channel.
If the reading count is set to infinity (INF), the scan will continuously repeat until you
stop it.
NOTE
One counter is used for STEP operation. As shown in Figure 7-1 , reading count
sets the Trigger Counter.
2750-900-01.book Page 9 Wednesday, August 3, 2011 7:56 AM