D-4 Signal Processing Sequence and Data Flow Model 2750 Multimeter/Switch System User’s Manual
OComp (offset-compensated ohms)
The Model 2750 performs a normal ohms measurement by sourcing a known current (I),
measuring the voltage (V), and then calculating the resistance (R = V/I). Offset-
compensated ohms cancels the effects of thermal EMFs which can adversely affect low-
resistance measurements.
With OCOMP enabled, the Model 2750 performs one normal resistance measurement,
and then loops back to perform a second resistance measurement with the internal current
source set to its lowest level. The offset-compensated ohms reading is then calculated as
shown in Figure D-2.
NOTE For details on OCOMP measurements, see “Offset-compensated ohms,”
page 3-20.
Filter
The filter is used to stabilize noisy readings. With the filter enabled, the specified number
of readings are averaged to yield a single filtered reading. There are two types of filters:
moving and repeating.
A filter stack is used to temporarily store the specified number of readings to be averaged.
In general, for the moving filter, each measurement process adds a reading to the stack
(oldest reading discarded), and then averages the stack to yield a filtered reading. For the
repeating filter, each measurement process fills the stack with new readings (all previous
readings discarded), and then averages the stack to yield a filtered reading.
NOTE For details on filter operation, see “Filter,” page 4-14.
Output trigger pulse (VMC)
An output trigger pulse from the Model 2750 can be used to trigger an external instrument
to perform an operation. In general, a trigger pulse is output at this point in flow chart for
each processed reading.
An exception is the SCAN function for scanning. For the SCAN function, an output trig-
ger is not output until after the specified number of channels (as set by the sample counter)
are scanned.
NOTE For details on scan operation, see “Trigger models,” page 7-4.
Rel
Next in the signal processing sequence is the Rel operation. Rel is used to null offsets, or
subtract a baseline rel value from the reading. With Rel enabled, the Rel’ed reading is cal-
culated as shown in Figure D-2.
NOTE For details on Rel operation, see “Relative,” page 5-2.
2750-900-01.book Page 4 Wednesday, August 3, 2011 7:56 AM
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