RST Instruments VW2100, Инструкция по эксплуатации, Страница: 7 / 34

VW2100 Vibrating Wire Piezometer
Instruction Manual
ELM0005P RST Instruments Ltd. Page 7
The VW2106 Readout Unit measures 100 cycles of vibration with a precise quartz
oscillator and displays a value proportional to the frequency squared, which is called
B-Units (Frequency
2
x 10
-3
). The relationship between B-Unit readings and the
pressure being exerted on the diaphragm is expressed by the following equation:
P = CF (L
0
– L)
where:
P = Corrected Pressure Reading
CF = Linear Calibration Factor in kPa\B-Unit digit. The CF is a unique value for
each manufactured VW sensor, as determined by the initial laboratory
calibration
L
0
= Initial B-Unit Reading at zero applied pressure on the diaphragm. The L
0
is a unique value for each manufactured VW sensor and is determined by
initial laboratory calibration
L = B-Unit Reading under the currently applied pressure on the diaphragm
The Vibrating Wire technology offers the unique advantage of frequency output
signal virtually unaffected by line impedance or contact resistance. Up to 1.5 km of
cable length can be used without signal deterioration.
3 C
ALIBRATION
All RST vibrating wire piezometers are individually calibrated in the laboratory before
shipment. Each vibrating wire piezometer is calibrated over its full working pressure
range. A Linear Calibration Factor (CF) is established by using the calibration data
points to do a linear regression. In addition, the calibration data is also fitted to a
polynomial regression which provides slightly more accurate data output over the full
reading range. Both formulas are provided on the instrument Calibration Record
sheet for use as appropriate. It is also noted that RST data loggers are set up to use
either formula to calculate the instrument output in engineering units.
As part of the calibration procedure, all vibrating wire piezometers are tested to
150% of the standard working range to prove their function at overpressure. The
sensor calibration is carried out over a temperature range of -20º C to +80º C which
proves their function at a wide temperature range and provides the input data for the
Temperature Correction Factor for each sensor.
A Calibration Record sheet is provided with each vibrating wire sensor for use in
calculating the applied loads on the vibrating wire sensors. The following general
information is contained in the Calibration Record sheet:
•
Model, Serial, and Manufacturing Numbers;
•
Pressure Range;
•
Temperature and Barometric Pressure at time of Calibration;