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Electronic Pressure Element - Resonant Wire Pressure Transducer |
In the design, a wire is gripped by a static member at one end, and by
the sensing diaphragm at the other. An oscillator circuit causes the
wire to oscillate at its resonant frequency. A change in process
pressure, changes the wire tension, which in turn changes the resonant
frequency of the wire. A digital counter circuit detects the shift.
Because this change in the frequency can be detected quite precisely,
this type of transducer can be used for low differential pressure
applications as well as to detect absolute and gauge pressures
Advantages
- It generates inherently digital signal; can be sent to a stable
crystal clock in microprocessor
Disadvantages - Sensitive to temperature, shock and vibration
variation, Nonlinear output signal
Resonant
Wire
 The resonant-wire pressure transducer was
introduced in the late 1970s. In this design (Figure ), a wire is
gripped by a static member at one end, and by the sensing diaphragm at
the other. An oscillator circuit causes the wire to oscillate at its
resonant frequency. A change in process pressure changes the wire
tension, which in turn changes the resonant frequency of the wire. A
digital counter circuit detects the shift. Because this change in
frequency can be detected quite precisely, this type of transducer can
be used for low differential pressure applications as well as to detect
absolute and gauge pressures.
The most significant advantage of the resonant wire pressure transducer
is that it generates an inherently digital signal, and therefore can be
sent directly to a stable crystal clock in a microprocessor. Limitations
include sensitivity to temperature variation, a nonlinear output signal,
and some sensitivity to shock and vibration. These
limitations typically are minimized by using a microprocessor to
compensate for nonlinearities as well as ambient and process temperature
variations.
Resonant wire transducers can detect absolute pressures from 10 mm Hg,
differential pressures up to 750 in. water, and gauge pressures up to
6,000 psig (42 MPa). Typical accuracy is 0.1% of calibrated span, with
six-month drift of 0.1% and a temperature effect of 0.2% per 1000¡ F.
.
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