Campbell CR3000 Micrologger, Operator'S Manual

Page: 408 / 644

Section 8. Operation
408
Measurements include the following:
•
Counts
•
Frequency (Hz)
•
Running average
Rotating magnetic-pickup sensors commonly generate ac voltage ranging from
thousandths of volts at low-rotational speeds to several volts at high-rotational
speeds. Terminals configured for low-level ac input have in-line signal
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. 604)
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. 409)
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.