Campbell CR6 Series, Operator'S Manual

Page: 442 / 690

Section 8. Operation
442
8.1.3.3 High-Frequency Measurements
High-frequency (square-wave) signals can be measured on U or C terminals.
Common sensors that output high-frequency include:
•
Photo-chopper anemometers
• Flow meters
Measurements include counts, frequency in hertz, and running average. Refer to
the section
Frequency Resolution
(p. 442)
for information about how the resolution
of a frequency measurement can be different depending on whether the
measurement is made with the PulseCount() or TimerInput() instruction.
U and C Terminals
•
See Pulse Counting Function — Specifications
(p. 110).
8.1.3.3.1 Frequency Resolution
Resolution of a frequency measurement made with the
PulseCount()
instruction
is calculated as
where
FR = resolution of the frequency measurement (Hz)
S = scan interval of CRBasic program
Resolution of a frequency measurement made with the TimerInput() instruction is
where
FR = frequency resolution of the measurement (Hz)
R = timing resolution of the TimerInput() measurement = 540 ns
P = period of input signal (seconds). For example, P = 1 / 1000 Hz = 0.001
s
E = Number of rising edges per scan or 1, whichever is greater.
Example: E for a 10 Hz input signal
Scan Rising Edge / Scan E
5.0 50 50
0.5 5 5
0.05 0.5 1