RST Instruments VW2100, Instruction Manual, Page: 8 / 34

VW2100 Vibrating Wire Piezometer
Instruction Manual
ELM0005P RST Instruments Ltd. Page 8
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Work Order Number;
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Cable Information (Length, Meter Markings, Color Code, and Type);
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Thermistor Type;
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Linear Calibration Factor (CF);
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Temperature Correction Factor (Tk);
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Polynomial Gauge Factors (A, B, and C);
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Calibration Data Table;
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Linear and Polynomial Formulas;
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Zero Reading, Temperature, and Barometric Pressure at time of Shipment;
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Calibration Certification.
Refer to Appendix A for an example of a Calibration Record sheet.
3.1 F
IELD
C
ALIBRATION
C
HECK
The following procedure can be used in the field to verify the validity of a vibrating
wire piezometer calibration as supplied on the Calibration Record sheet.
Note that VW2100 piezometers will require the filter stone to be saturated prior to
calibration. Place the VW2100 piezometer in water to saturate the filter stone.
Ensure the entire space between the instrument diaphragm and the filter stone is
filled with water. Refer to Appendix B for more detailed information on the saturation
of VW2100 piezometers with Casagrande style filters, and VW2100-DP piezometers.
1
Lower the piezometer to depth in a vertical, water filled borehole using the cable
markings to accurately control and set the depth. A minimum emersion depth of
10 m is recommended to ensure adequate accuracy of the field calibration check.
2
Allow 20 to 30 minutes for the piezometer to come to complete thermal
equilibrium in the borehole. Record the B-unit and temperature readings at that
depth using an RST VW2106 readout unit.
3
Raise the piezometer a known amount while keeping it fully submerged. If the
temperature reading is changing, allow the instrument to come to the new
thermal equilibrium. This may take another 20 to 30 minutes.
4
Record the new B-Unit and temperature readings at the higher elevation.
Calculate the instrument Calibration Factor (CF) (kPa per B-Unit) from this
information, given the change in pressure head and B-Unit readings.
5
Compare this field calibration to the calibration factor value provided on the
Calibration Record sheet. The two values should agree within ± 0.5%. Repeat
this calibration check as required to confirm the sensor is in proper working
condition.