Campbell Scientific CR200/CR200X-series Dataloggers - Manual (Page 38)

Section 3. Overview
Period Average: 4 channels (SE 1–4)
• Maximum input voltage: 4000 mV.
• Maximum frequency: 150 kHz
• Voltage threshold: counts cycles on transition from < 900 mV to >
2100 mV.
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 CR200(X) 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 a correct signal.
Period average measurements utilize 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.
Pulse: 2 channels (P_SW, P_LL) configurable for counts or frequency of the
following signal types:
• High level square waves (P_SW)
• Switch closures (P_SW)
• Low-level A/C sine waves (P_LL)
Digital I/O: 2 channels (C1 - C2) configurable for SDI-12 communication,
state, frequency, and pulses. 5 analog channels (SE1–SE5) configurable for
input/output.
• C1 - C2: state, frequency, pulse.
• C1: SDI-12 input/output, state, frequency, pulse.
• SE 1–5: input/output, state.
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