Campbell CR800 Series, Operator'S Manual

Page: 373 / 598

Section 8. Operation
373
conditioning for measuring signals ranging from 20 mV RMS ( ± 28 mV peak-to-
peak) to 14 V RMS (
±
20 V peak-to-peak).
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 Pulse
Input Modules — List
(p. 562)
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. 374)
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 k
Ω
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.