Common sensors that output high-frequency pulses include:
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Photo-chopper anemometers
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Flow meters
Measurement output optionss include counts, frequency in hertz, and running average.
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CRBasic instruction: PulseCount()
18.5.3 Switch-closure and open-collector measurements
Switch-closure and open-collector (also called current-sinking) signals can be measured on
terminals:
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P_SW or C
Mechanical switch-closures have a tendency to bounce before solidly closing. Unless filtered,
bounces can cause multiple counts per event. The data logger automatically filters bounce.
Because of the filtering, the maximum switch-closure frequency is less than the maximum high-
frequency measurement frequency. Sensors that commonly output a switch-closure or an open-
collector signal include:
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Tipping-bucket rain gages
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Switch-closure anemometers
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Flow meters
Data output options include counts, frequency (Hz), and running average.
18.5.3.1 P_SW Terminal
An internal 47 kΩ pull-up resistor pulls an input to 3.3 VDC with the switch open, whereas a
switch-closure to ground pulls the input to 0 V.
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CRBasic instruction: PulseCount(). See the CRBasic Editor help for detailed instruction
information and program examples: https://help.campbellsci.com/crbasic/cr300/ .
18. Measurements104
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