Section 5. Overview
5.2.4 Period Averaging — Overview
Related Topics:
• Period Average Measurements — Specifications
• Period Average Measurements — Overview
(p. 73)
• Period Average Measurements — Details (p. 383)
CR800 SE terminals can be configured to measure period average.
Note Both pulse count and period average measurements are used to
measure frequency output sensors. Yet pulse count and period average
measurement methods are different. Pulse count measurements use
dedicated hardware — pulse count accumulators, which are always
monitoring the input signal, even when the CR800 is between program
scans. In contrast, period average measurement instructions only monitor
the input signal during a program scan. Consequently, pulse count scans
can usually be much less frequent than period average scans. Pulse
counters may be more susceptible to low-frequency noise because they
are always "listening", whereas period averaging 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.
Period average measurements use 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, as compared to pulse count measurements. The
frequency resolution of pulse count measurements can be improved by
extending the measurement interval by increasing the scan interval and by
averaging. For information on frequency resolution, see Frequency
Resolution
(p. 374).
5.2.5 Vibrating Wire Measurements — Overview
Related Topics:
• Vibrating Wire Measurements — Specifications
• Vibrating Wire Measurements — Overview
(p. 73)
• Vibrating Wire Measurements — Details
(p. 382)
Vibrating wire sensors are the sensor of choice in many environmental and
industrial applications that need sensors that will be stable over very long periods,
such as years or even decades. The CR800 can measure these sensors either
directly or through interface modules.
A thermistor included in most sensors can be measured to compensate for
temperature errors.
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