Switch-Closure And Open-Collector Measurements; P_Sw Terminal; C Terminals - Campbell CR300 Series Product Manual

14.5.3 Switch-closure and open-collector measurements

Switch-closure and open-collector (also called current-sinking) signals can be measured on
terminals:
P_SW or C
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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:
Tipping-bucket rain gages
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Switch-closure anemometers
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Flow meters
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Data output options include counts, frequency (Hz), and running average.

14.5.3.1 P_SW Terminal

An internal 100 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.
CRBasic instruction: PulseCount(). See the CRBasic Editor help for detailed instruction
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information and program examples:
Switch Closure on P Terminal

14.5.3.2 C terminals

Switch-closure measurements on C terminals require a 100 kΩ pull-up resistor to 12 V. Switch-
closure mode is a special case edge-count function that measures dry-contact switch-closures or
open collectors. The operating system filters bounces.
https://help.campbellsci.com/crbasic/cr300/.
Open Collector on P Terminal
14. Measurements 81