internal comparator without the need for additional input conditioning circuitry. The threshold
allows direct connection of standard digital signals, but it is not recommended for small-
amplitude sensor signals.
A threshold other than zero results in offset voltage drift, limited accuracy (approximately ±10
mV) and limited resolution (approximately 1.2 mV).
See also Period-averaging measurement specifications (p. 168).
TIP:
Both pulse count and period-average measurements are used to measure frequency output
sensors. However, their measurement methods are different. Pulse count measurements use
dedicated hardware - pulse count accumulators, which are always monitoring the input
signal, even when the datalogger is between program scans. In contrast, period-average
measurements use program instructions that only monitor the input signal during a program
scan. Consequently, pulse count scans can occur less frequently than period-average scans.
Pulse counters may be more susceptible to low-frequency noise because they are always
"listening", whereas period-averaging measurements may filter the noise by reason of being
"asleep" most of the time.
Pulse count measurements are not appropriate for sensors that are powered off between
scans, whereas period-average measurements work well since they can be placed in the scan
to execute only when the sensor is powered and transmitting the signal.
6.6 Pulse measurements
The output signal generated by a pulse sensor is a series of voltage waves. The sensor couples its
output signal to the measured phenomenon by modulating wave frequency. The datalogger
detects the state transition as each wave varies between voltage extremes (high-to-low or low-to-
high). Measurements are processed and presented as counts, frequency, or timing data. Both
pulse count and period-average measurements are used to measure frequency-output sensors.
For more information, see Period-averaging measurements (p. 70).
6. Measurements 71
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