Section 5: Basic Digital Multimeter (DMM) Operation
Series 3700 System Switch/Multimeter User's Manual
5-4
3700S-900-01 Rev. C / July 2008
NOTE
To force a rapid update of the internal reference points, set the
AUTOZERO attribute for the channel to ONCE. This will update the
internal reference points once and stop. Querying the AUTOZERO
setting will show it set to OFF. The Instrument Control Library (ICL)
command to set AUTOZERO is covered in dmm.autozero.
The dmm.autozero=dmm.AUTOZERO_ONCE or 2 has significant
delay for dmm.nplc settings <0.2plc. Refer to the table below for delay
time at selected NPLC.
timer.reset()
dmm.autozero=2
time=timer.measure.t()
print(time)
NPLC
Delay time (s)
0.0005 2.75
0.199 5.45
Remote programming can be used to enable or disable autozero. Autozero can
be configured from the front panel by pressing the
CONFIG
key, then the
DMM
key (configuration includes: OFF, ON, or ONCE). See dmm.autozero for remote
programming information.
Line cycle synchronization
Synchronizing A/D conversions with the frequency of the power line increases
common mode and normal mode noise rejection. When line cycle
synchronization is enabled, the measurement is initiated at the first positive-
going zero crossing of the power line cycle after the trigger.
The following figure shows a measurement process that consists of two A/D
conversions. If the trigger occurs during the positive cycle of the power line
(Trigger #1), the A/D conversion starts with the positive-going zero crossing of
the power line cycle. If the next trigger (Trigger #2) occurs during the negative
cycle, then the measurement process also starts with the positive-going zero
crossing.
NOTE
Line synchronization is not available for the AC functions (ACV, ACI,
FREQ, or PERIOD). Line synchronization can be enabled for any DC
function and any NPLC measurement, increasing NMRR and CMRR.
See dmm.linesync in the Reference Manual for remote programming
information.