NOTE:
Take precautions against ground loops when measuring sensors that require AC excitation.
See also
For more information, see
Accuracy for resistance measurements
6.3.5 Accuracy for resistance measurements
Consult the following technical papers for in-depth treatments of several topics addressing
voltage measurement quality:
l
Preventing and Attacking Measurement Noise Problems
l
Benefits of Input Reversal and Excitation Reversal for Voltage Measurements
l
Voltage Measurement Accuracy, Self- Calibration, and Ratiometric Measurements
NOTE:
Error discussed in this section and error-related specifications of the CR6 do not include error
introduced by the sensor, or by the transmission of the sensor signal to the data logger.
For accuracy specifications of ratiometric resistance measurements, see
(p. 218). Voltage measurement is variable V
1
or V
2
in resistance measurements.
Offset is the same as that for simple analog voltage measurements.
Assumptions that support the ratiometric-accuracy specification include:
l
Data logger is within factory calibration specification.
l
Input reversal for differential measurements and excitation reversal for excitation voltage
are within specifications.
l
Effects due to the following are not included in the specification:
o
Bridge-resistor errors
o
Sensor noise
o
Measurement noise
6.4 Period-averaging measurements
Use
PeriodAvg()
to measure the period (in microseconds) or the frequency (in Hz) of a signal
on a single-ended channel. For these measurements, the data logger uses a high-frequency
digital clock to measure time differences between signal transitions, whereas pulse-count
measurements simply accumulate the number of counts. As a result, period-average
measurements offer much better frequency resolution per measurement interval than pulse-
count measurements. See also
U terminals on the data logger are configurable for measuring the period of a signal.
6. Measurements
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