Switch-closure and open-collector measurements

Switch-closure and open-collector (also called current-sinking) signals can be measured on terminals:

P_SW or C1 to C2 or SE 1 to SE4

NOTE:

Switch closure on C1 to C2, or SE1 to SE4 requires a 100 kΩ pull-up resistor.

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
Switch-closure anemometers
Flow meters

Data output options include counts, frequency (Hz), and running average.

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.

CRBasic instruction: PulseCount(). See the CRBasic Editor help for detailed instruction information and program examples: https://help.campbellsci.com/crbasic/cr350/ .

Switch Closure on P Terminal	Open Collector on P Terminal

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.

CRBasic instruction: PulseCount().