subsequent measurement. For differential measurements without input reversal, this offset
voltage measurement is performed as part of the routine background calibration of the data
logger (see
(p. 110)). Single-ended measurement instructions
VoltSE()
and
TCSe()
include the
MeasOff
parameter determines whether the offset
voltage measured is done at the beginning of the measurement instruction, or as part of self-
calibration. This option provides you with the opportunity to weigh measurement speed against
measurement accuracy. When
MeasOff = True
, a measurement of the single-ended offset
voltage is made at the beginning of the
VoltSE()
or
TCSe()
instruction. When
MeasOff =
False
, measurements will be corrected for the offset voltage determined during self-calibration.
For installations experiencing fluctuating offset voltages, choosing
MeasOff = True
for the
VoltSE()
or
TCSe()
instruction results in better offset voltage performance.
If
RevDiff
,
RevEx
, or
MeasOff
is disabled ( = False), offset voltage compensation is
automatically performed, albeit less effectively, by using measurements from the background
calibration. Disabling
RevDiff
,
RevEx
, or
MeasOff
speeds up measurement time; however,
the increase in speed comes at the cost of accuracy because of the following:
l
RevDiff
,
RevEx
, and
MeasOff
are more effective.
l
Background calibrations are performed only periodically, so more time skew occurs
between the background calibration offsets and the measurements to which they are
applied.
NOTE:
When measurement duration must be minimal to maximize measurement frequency,
consider disabling
RevDiff
,
RevEx
, and
MeasOff
when data logger temperatures and
return currents are slow to change.
9.11 Field calibration
Calibration increases accuracy of a measurement device by adjusting its output, or the
measurement of its output, to match independently verified quantities. Adjusting sensor output
directly is preferred, but not always possible or practical. By adding the
FieldCal()
or
FieldCalStrain()
instruction to a CRBasic program, measurements of a linear sensor can
be adjusted by modifying the programmed multiplier and offset applied to the measurement,
without modifying or recompiling the CRBasic program. See the CRBasic Editor help for detailed
instruction information and program examples:
https://help.campbellsci.com/crbasic/cr6/.
9. Tips and troubleshooting
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