Campbell CR6 - Pulse Measurement Tips; Input Filters and Signal Attenuation

Counting modes:
l Counting the increase on rising edge of channel A when channel A leads channel B.
Counting the decrease on falling edge of channel A when channel B leads channel A.
l Counting the increase at each rising and falling edge of channel A when channel A leads
channel B. Counting the decrease at each rising and falling edge of channel A when
channel A leads channel B.
l Counting the increase at each rising and falling edge of both channels when channel A
leads channel B. Counting the decrease at each rising and falling edge of both channels
when channel B leads channel A.
For more information, see Pulse measurement specifications (p. 221).
6.5.6 Pulse measurement tips
The PulseCount() instruction uses dedicated 32-bit counters to accumulate all counts over
the programmed scan interval. The resolution of pulse counters is one count. Counters are read
at the beginning of each scan and then cleared. Counters will overflow if accumulated counts
exceed 4,294,967,296 (2
32
), resulting in erroneous measurements. See the CRBasic Editor help for
detailed instruction information and program examples:
https://help.campbellsci.com/crbasic/cr6/.
Counts are the preferred PulseCount() output option when measuring the number of tips
from a tipping-bucket rain gage or the number of times a door opens. Many pulse-output
sensors, such as anemometers and flow meters, are calibrated in terms of frequency (Hz) so are
usually measured using the PulseCount() frequency-output option.
Use the LLAC4 module to convert non-TTL-level signals, including low-level ac signals, to TTL
levels for input to C terminals
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().
Understanding the signal to be measured and compatible input terminals and CRBasic
instructions is helpful. See Pulse input terminals and the input types they can measure (p. 79).
6.5.6.1 Input filters and signal attenuation
Terminals configured for pulse input have internal filters that reduce electronic noise. The
electronic noise can result in false counts. However, input filters attenuate (reduce) the amplitude
(voltage) of the signal. Attenuation is a function of the frequency of the signal. Higher-frequency
signals are attenuated more. If a signal is attenuated too much, it may not pass the detection
6. Measurements 84