Geosense VW PIEZOMETERS, Инструкция по эксплуатации

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Version 1.4 May 09
1.2 Theory of Operation
The Vibrating Wire Piezometer consists of a tensioned steel wire, anchored at one
end to a flexible diaphragm ( the sensing element ) and at the other end to the
Nimonic inner body, all sealed into a stainless steel body. The internal parts of all
MGS Geosense piezometers are identical, only the thickness of the diaphragm and
the geometry of the body changes.
Two opposing coils are located within the inner Nimonic body close to the axis of the
wire. When a brief voltage excitation, or swept frequency excitation is applied to the
coils, a magnetic field is induced causing the wire to oscillate at its’ resonant
frequency. The wire continues to oscillate for a short period through the ‘field’ of the
permanent magnet, thus generating an alternating current (sinusoidal) output. The
frequency of this current output is detected and processed by a vibrating wire readout
unit, or by a data logger equipped with a vibrating wire interface, where it can be
converted into ‘Engineering’ units of pressure.
As fluid pressure is applied to the exposed side of the flexible diaphragm, the
diaphragm deflects, causing a change in the tension of the wire behind it. The change
in tension of the wire results in a change in resonant frequency of oscillation of the
wire, with the square of frequency of oscillation being directly proportional to the
applied pressure.
For further information see Section 6 - Data Handling.