Terminals configured for pulse input have internal filters that reduce electronic noise, and thus
reduce false counts. Internal ac coupling is used to eliminate dc offset voltages. For tips on
working with pulse measurements, see Pulse measurement tips (p. 77).
For more information, see Pulse measurement specifications (p. 169).
6.6.1 Low-level ac measurements
Low-level ac (alternating current or sine-wave) signals can be measured on P terminals. Ac
generator anemometers typically output low-level ac.
Measurements include the following:
l Counts
l Frequency (Hz)
l 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.
CRBasic instruction: PulseCount()
Low-level ac signals cannot be measured directly by C terminals. Peripheral terminal expansion
modules, such as the Campbell Scientific LLAC4, are available for converting low-level ac signals
to square-wave signals measurable by C terminals.
For more information, see Pulse measurement specifications (p. 169).
6.6.2 High-frequency measurements
High-frequency (square-wave) signals can be measured on P or C terminals. Common sensors
that output high-frequency pulses include:
l Photo-chopper anemometers
l Flow meters
Measurements include counts, frequency in hertz, and running average. Note that the resolution
of a frequency measurement can be different depending on the terminal used in the
PulseCount() instruction. See the CRBasic help for more information.
The datalogger has built-in pull-up and pull-down resistors for different pulse measurements
which can be accessed using the PulseCount()instruction. Note that pull down options are
usually used for sensors that source their own power.
See Pulse measurement specifications (p. 169) for more information.
6. Measurements 73
To Next Page
Loading...
Need help?
General
