f
= frequency (Hz)
t
= temperature (°C)
A, B, C, D, E, F = user-specified coefficients (constants)
For correct calculations, sensor documentation must provide data to discern which coefficients of
the polynomial are relevant (A, B, C, D, E, or F); all other coefficients must be set to 0 so that they
have no impact on the output calculation. Do this by comparing the calculation equations of your
sensor manual to the polynomials previously shown. Contact your Campbell Scientific support
representative if you require assistance for this step. The polynomial coefficient schemes have
already been determined for the most common sensor types, and these can be shared.
Enter your sensor-specific coefficients in
Device Configuration Utility
. See
Device Configuration
Utility
help for more information.
Once the settings have been applied and the CRVW3 restarts, the calculated output in
engineering units will be given in the ChanX_EngOut value of the VW_Data output table, where
X
represents the channel number, unless “ChanX” is the name you gave to the sensor/channel.
D.2 Sensor calibration
To enable in-field CRVW3 calibration, set Use Baseline Offsets to True, or set Use Ambient
Pressure Correction to True.
Once these settings have been applied, the CRVW3 will restart, and the calibration functionality
will be operational. To perform a calibration, use the Calibration Wizard, which is found using
LoggerNet
Connect Screen Datalogger menu.
For more information about the calibration process and using the Calibration Wizard, see the
RTDAQ
or
LoggerNet
manual:
/documents/us/manuals/rtdaq.pdf
/documents/us/manuals/loggernet.pdf
Disregard the discussion of the
FieldCal
CRBasic instruction in this documentation. However,
the process of manual calibration described in those sections can be performed using the Public
table of the CRVW3.
The Use Baseline Offsets setting enables engineering output to be adjusted using stored baseline
values, such as datum or zero-condition readings. Baseline values for frequency, temperature,
and pressure will be stored via the Calibration Wizard, where applicable, and used for output
calculations. The offset value is subtracted from the calculated value to obtain the final output.
The Use Ambient Pressure Correction setting controls whether engineering output will be
adjusted using the current atmospheric pressure value that is stored in certain variables in the
CRVW3 3-Channel Vibrating-Wire Data Logger
83