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2
directly proportional to the pressure applied to the
magnet, another with a pole piece, are located close to the wire. In use, a pulse of
varying frequency (swept frequency) is applied to the coils and this causes the wire to
vibrate primarily at its resonant frequency. When excitation ends the wire continues to
vibrate and a sinusoidal AC electrical signal, at the resonant frequency, is induced in the
coils and transmitted to the readout box where it is conditioned and displayed.
To prevent damage to the sensitive diaphragm a filter is used to keep out solid particles.
. Standard filters are 50 micron stainless steel; high air entry value tips are available on
request.
All exposed components are made of corrosion resistant stainless steel and, if proper
installation techniques are used, the device should have an unlimited life. In salt water it
may be necessary to use special materials for the diaphragm and housing.
Portable readout units are available to provide the excitation, signal conditioning and
readout of the instrument. Datalogging systems are also available for remote
unattended data collection of multiple sensors. Contact Geokon for additional
information.
Calibration data are supplied with each piezometer for conversion of gage readings to
engineering units and for temperature corrections see Section 5.
3 INSTALLATION
3.1 Preliminary Tests
Upon receipt of the piezometer the zero reading should be checked and noted (see
Sections 3.1 to 3.3 for readout instructions). A Model 4700 VW Temperature Sensor is
included inside the body of the sensor for the measurement of temperature (see Section
5 for instructions).
Calibration data are supplied with each gage and zero readings at six different
temperatures and barometric pressure, is included. Zero readings at the site should
coincide with the calibration zero readings within +/- 50 digits after barometric and
temperature corrections are made. The factory elevation is +580 ft. Before March 21,
1995 factory barometric pressure readings were corrected to sea level; readings after
this date represent absolute pressure. (Barometric pressure changes with elevation at a
rate of ½ psi per 1,000 ft.) See Section 5 for sample calibration sheets.
diaphragm. Two coils, one with a
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