Campbell CR3000 Micrologger, Руководство оператора

Страница: 413 / 644

Section 8. Operation
413
The PulseCount() instruction, whether measuring pulse inputs on P or C
terminals, uses dedicated 24-bit counters to accumulate all counts over the
programmed scan interval. The resolution of pulse counters is one count or 1 Hz.
Counters are read at the beginning of each scan and then cleared. Counters will
overflow if accumulated counts exceed 16,777,216, resulting in erroneous
measurements.
•
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
(p. 542)
) so are
usually measured using the PulseCount() frequency-output option.
•
Accuracy of PulseCount() is limited by a small scan-interval error of
±(3 ppm of scan in 10 µs), plus the measurement resolution error
of ±1 / (scan interval). The sum is essentially ±1 / (scan interval).
•
Use the LLAC4
(p. 604)
module to convert non-TTL-level signals,
including low-level ac signals, to TTL levels for input into C terminals.
•
As shown in the table Switch Closures and Open Collectors
(p. 413),
C
terminals, with regard to the 6.2 V Zener diode, have an input resistance
of 100 kΩ with input voltages < 6.2 Vdc. For input voltages ≥ 6.2 Vdc,
C
terminals have an input resistance of on
ly 220 Ω.
Switch Closures and Open Collectors on P Terminals
Switch Closure on P Terminal
Open Collector on on P Terminal
Switch Closures and Open Collectors
Switch Closure on C Terminal:
No Pull-Up