49
CALCULATION
USING LINEAR
EQUATION
CALCULATION
USING
POLYNOMIAL
EQUATION
The mathematical relationship between the resonance frequency of
a tensioned wire and the force applying the tension is represented by
a near straight line relationship between the square of the frequency
(Hz
2
) and the applied force.
The sensor readings in frequency can be converted to measurements
in engineering units (such as mm, kPa or psi) using the following
equations:
The following equation is used for readings in Hz
2
/1000:
E = G x (R0 - R1)
where:
E
is the resultant Engineering unit
G
is the linear Gauge factor for the units of calibration
R0
is the ‘base’ or ‘zero’ reading (in Hz
2
/1000) taken at the time
of installation
R1
is the current reading in Hz
2
/1000.
The polynomial formula for all Soil Instruments VW sensors is:
E = A x R1
2
+ B x R1 + C
where:
E
is the resultant value in Engineering units
A, B
and
C
are the polynomial factors from the calibration sheet
R1
is the current reading in Hz
2
/1000
It should be noted that
C
is an offset value derived from a ‘base’
reading in the factory where the sensor calibration is performed.
Soil Instruments recommend the value for
C
should be recalculated
at the time of installation from the
R0
as follows:
C = - (A x R0
2
+ B x R0)
VWnote allows you to enter either
C
or
R0
in the sensor configuration.
If you choose to enter
R0
, the VWnote will recalculate the
C
for you
before performing the raw to engineering unit conversion.
Calculation of engineering units from frequency readings of VW sensors
Summary of Contents for RO-1 VW Note
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