P Terminals
• Maximum input frequency is dependent on input voltage:
o 1.0 to 20 Hz at 20 mV RMS
o 0.5 to 200 Hz at 200 mV RMS
o 0.3 to 10 kHz at 2000 mV RMS
o 0.3 to 20 kHz at 5000 mV RMS
• CRBasic instruction: PulseCount()
Internal ac coupling is used to eliminate dc-offset voltages of up to ±0.5 Vdc.
C Terminals
Low-level ac signals cannot be measured directly by C terminals. Refer to the
appendix Pulse Input Modules List
(p. 646) for information on peripheral terminal
expansion modules available for converting low-level ac signals to square-wave
signals.
8.1.3.3 High-Frequency Measurements
High-frequency (square-wave) signals can be measured on P 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. 353) for information about how the resolution
of a frequency measurement can be different depending on whether the
measurement is made with the PulseCount() or TimerIO() instruction.
•
P Terminals
• Maximum input frequency = 250 kHz
• CRBasic instructions: PulseCount()
High-frequency pulse inputs are routed to an inverting CMOS input buffer with
input hysteresis. The CMOS input buffer is at output 0 level with inputs ≥ 2.2 V
and at output 1 level with inputs ≤ 0.9 V. An internal 100 kΩ resistor is
automatically connected to the terminal to pull it up to 5 Vdc. This pull-up
resistor accommodates open-collector (open-drain) output devices.
C Terminals
• Maximum input frequency = <1 kHz
• CRBasic instructions: PulseCount(), TimerIO()
8.1.3.3.1 Frequency Resolution
Resolution of a frequency measurement made with the PulseCount() instruction
is calculated as
353
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