Switch-closure and open-collector measurements

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

• P 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:

• Tipping-bucket rain gages
• Switch-closure anemometers
• Flow meters

The data logger has built-in pull-up and pull-down resistors for different pulse measurements which can be accessed using the PulseCount() instruction. Note that pull down options are usually used for sensors that source their own power.

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

P Terminals

An internal 100 kΩ pull-up resistor pulls an input to 5 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/cr1000x/ .

Switch Closure on P Terminal	Open Collector on P Terminal

C terminals

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().

See also Pulse measurement specifications.