Input Filters And Signal Attenuation; Pulse Count Resolution; Vibrating Wire Measurements; Vspect - Campbell CR300 Series Product Manual

18.5.5.1 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
thresholds required by the pulse count circuitry.See
for more information. The listed pulse measurement specifications account for attenuation due
to input filtering.

18.5.5.2 Pulse count resolution

Longer scan intervals result in better resolution.
On a 1 second scan, the resolution is 1 pulse per second. The resolution on a 10 second scan
interval is 1 pulse per 10 seconds, which is 0.1 pulses per second. The resolution on a 100
millisecond interval is 10 pulses per second.
For example, if a flow sensor outputs 4.5 pulses per second and you use a 1 second scan, one
scan will have 4 pulses and the next 5 pulses. Scan to scan, the flow number will bounce back and
forth. If you did a 10 second scan (or saved a total to a 10 second table), you would get 45 pulses.
The total is 45 pulses for every 10 seconds. An average will correctly show 4.5 pulses per second.
You wouldn't see the reading bounce on the longer time interval.

18.6 Vibrating wire measurements

The data logger can measure vibrating wire sensors through vibrating-wire interface modules.
Vibrating wire sensors are the sensor of choice in many environmental and industrial applications
that need sensor stability over very long periods, such as years or even decades. A thermistor
included in most sensors can be measured to compensate for temperature errors.
18.6.1 VSPECT®
Measuring the resonant frequency by means of period averaging is the classic technique, but
Campbell Scientific has developed static and dynamic spectral-analysis techniques (VSPECT) that
produce superior noise rejection, higher resolution, diagnostic data, and, in the case of dynamic
VSPECT, measurements up to 333.3 Hz. For detailed information on VSPECT, see
Spectral Analysis Technology
Pulse measurement
PulseCount()
.
specifications (p. 247)
resolution is 1 pulse per scan.
Vibrating Wire
18. Measurements 107