Using the PulseCount() instruction, P_LL, P_SW, SE 1-4, and C terminals are configurable for
pulse input to measure counts or frequency. Maximum input frequency is dependent on input
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.
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(p. 106).
Output can be recorded as counts, frequency or a running average of frequency.
See also Pulse measurement specifications(p. 247).
See the CRBasic Editor help for detailed instruction information and program examples:
https://help.campbellsci.com/crbasic/cr300/ .
18.5.1 Low-level AC measurements
Low-level AC (alternating current or sine-wave) signals can be measured on P_LL terminals. AC
generator anemometers typically output low-level AC.
Measurement output options include the following:
l
Counts
l
Frequency (Hz)
l
Running average
Rotating magnetic-pickup sensors commonly generate AC voltage ranging from millivolts at
low-rotational speeds to several volts at high-rotational speeds.
CRBasic instruction: PulseCount(). See the CRBasic Editor help for detailed instruction
information and program examples: https://help.campbellsci.com/crbasic/cr300/ .
Low-level AC signals cannot be measured directly by C terminals. Peripheral terminal expansion
modules, such as the Campbell Scientific LLAC4, are available for converting low-level AC signals
to square-wave signals measurable by C terminals.
For more information, see Pulse measurement specifications(p. 247).
18.5.2 High-frequency measurements
High-frequency (square-wave) signals can be measured on terminals:
l
P_LL, P_SW, SE 1-4 or C
18. Measurements103
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