Campbell CR3000 Micrologger, Руководство оператора

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Section 8. Operation
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4.997 mV. Subtracting the second sub-measurement from the first and then
dividing by 2 cancels the offset:
5.003 mV – (–4.997 mV) = 10.000 mV
10.000 mV / 2 = 5.000 mV
When the CR3000 reverses differential inputs or excitation polarity, it delays the
same settling time after the reversal as it does before the first sub-measurement.
So, there are two delays per measurement when either RevDiff or RevEx is used.
If both RevDiff and RevEx are True, four sub-measurements are performed;
positive and negative excitations with the inputs one way and positive and
negative excitations with the inputs reversed. The automatic procedure then is as
follows,
1. Switches to the measurement terminals
2. Sets the excitation, and then settle, and then measure
3. Reverse the excitation, and then settles, and then measure
4. Reverse the excitation, reverse the input terminals, settle, measure
5. Reverse the excitation, settle, measure
There are four delays per measure. The CR3000 processes the four sub-
measurements into the reported measurement. In cases of excitation reversal,
excitation time for each polarity is exactly the same to ensure that ionic sensors do
not polarize with repetitive measurements.
Read More A white paper entitled "The Benefits of Input Reversal and
Excitation Reversal for Voltage Measurements" is available at
www.campbellsci.com.
Ground Reference Offset Voltage
When MeasOff
is enabled (=
True), the CR3000 measures the offset voltage of
the ground reference prior to each VoltSe() or TCSe() measurement. This offset
voltage is subtracted from the subsequent measurement.
From Auto Self-Calibration
If RevDiff, RevEx, or MeasOff
is disabled (=
False), offset voltage compensation
is continues to be automatically performed, albeit less effectively, by using
measurements from the auto self-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:
1 RevDiff, RevEx, and MeasOff are more effective.
2 Auto self-calibrations are performed only periodically, so more time skew
occurs between the auto self-calibration offsets and the measurements to
which they are applied.