E-1
Appendix E. Engineering Output and
Calibration
The basic measurement outputs given by the CRVW3 are sensor frequency and
sensor temperature (if a thermistor is used). These values can be used both to
calculate an output value in engineering units, as well as to form the basis for
calibration adjustments that are stored and applied to the outputs.
E.1 Engineering Output
The frequency reading on the CRVW3 is expressed both in units of Hertz (Hz)
and in units of digits (Hz
2
/1000). The CRVW3 can be configured to calculate
an output value that is specified in engineering units (in units of measure or
dimensions). Examples of units are kPa, millibar, mmHg, mmH20, inches, feet,
or meters for piezometers, µε (microstrain) or ε (strain) for strain gages,
kilograms, tons, or pounds for load cells, mm or inches for crackmeters, and so
forth. The CRVW3 implements a polynomial that works with most vibrating-
wire sensors, and uses frequency and temperature as inputs.
The sensor manual should include information that describes the process of
converting a frequency and temperature value pair into engineering output.
Sometimes the temperature value is not used. You should study the manual
carefully to understand what factors are used to make these calculations.
Constants involved in the calculation are often slightly different for each
manufactured sensor, in which case a calibration sheet or calibration record
will be provided with each individual sensor. You will need this information
when configuring the settings of the CRVW3 to obtain the desired result. You
should work out most of the details for calculating engineering output by using
typical sensors in the lab or office. This will help ensure that the field
deployment process will proceed as smoothly as possible.
The settings used on the CRVW3 to configure engineering output are found on
the
Channel1
,
Channel2
, and
Channel3
tabs of the
Settings Editor
tab in
DevConfig
, discusses basic
information for using
DevConfig
to configure the CRVW3.
If you will use a temperature reading as part of the output calculation, you
should set
Thermistor Enabled
to
True
, and enter the thermistor coefficient
A, B
,
and C values for Steinhart-Hart conversion. You can’t use a temperature
reading as part of the calculation unless it is expressed in units of Degrees
Celsius (raw resistance in Ohms will not work).
Enable the calculation to occur by setting
Calculate Engineering Output
to
True
. Enter the desired output units in the
Engineering Units
box. This is a
string representing the units of measure for the calculated output values (mm,
feet, kilograms, kPa,
µε, etc.).
If your sensor manual uses digits as the frequency input for calculating
engineering units, set the
UseDigits
setting to
True
. At that point, the
polynomial used for calculation will be based on digits and temperature, and
frequency in Hz will
not
be used. When
UseDigits
is
False
, the polynomial
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