Pulse measurements

The output signal generated by a pulse sensor is a series of voltage waves. The sensor couples its output signal to the measured phenomenon by modulating wave frequency. The data logger detects the state transition as each wave varies between voltage extremes (high-to-low or low-to-high). Measurements are processed and presented as counts, frequency, or timing data. Both pulse count and period-average measurements are used to measure frequency-output sensors. For more information, see Period-averaging measurements.

The data logger includes terminals that are configurable for pulse input as shown in the following image.

Pulse input terminals and the input types they can measure
Input type	Pulse input terminal
High-frequency	C (all) U (all)
Low-level AC	U (even numbered terminals)
Switch-closure	P1 P2 C (all) U (all)

Using the PulseCount() instruction, U and C terminals are configurable for pulse input to measure counts or frequency. Maximum input frequency is dependent on signal voltage. If pulse input voltages exceed the maximum voltage, third-party external-signal conditioners should be employed. Do not measure voltages greater than 20 V.

NOTE:

Conflicts can occur when a control port pair is used for different instructions (TimerInput(), PulseCount(), SDI12Recorder(), WaitDigTrig()). For example, if C1 is used for SDI12Recorder(), C2 cannot be used for TimerInput(), PulseCount(), or WaitDigTrig().

U terminals configured for pulse input have internal filters that reduce electronic noise, and thus reduce false counts. Internal AC coupling is used to eliminate DC offset voltages. For tips on working with pulse measurements, see Pulse measurement tips.

Output can be recorded as counts, frequency or a running average of frequency.

For more information, see Pulse measurement specifications.

See the CRBasic Editor help for detailed instruction information and program examples: https://help.campbellsci.com/crbasic/cr6/ .