Resonant Wire Pressure Transducer

The resonant-wire pressure transducer is a device generally employed for measurement of pressure in industrial applications. It was brought out in the late 1970s. The figure below shows a typical resonant wire type differential pressure transducer. In this design there are:

  1. Resonant wire
  2. High-pressure diaphragm
  3. Low-pressure diaphragm
  4. Magnets
  5. Metal tube
  6. High side backup plate
  7. Low side backup plate
  8. Electrical insulator
  9. Preload spring
  10. Fluid transfer port
  11. Oscillator circuit

 


Operating Principle

In a resonant wire pressure transducer, a wire is fixed by a static member at one end, and by a pressure sensing diaphragm at the other (under tension). The process pressures are detected by high pressure and low pressure diaphragms on the right and left of the unit. The wire is positioned in a magnetic field and allowed to oscillate. The oscillator circuit results in the oscillation of wire at its resonant frequency. The variations in process pressure affects the wire tension, due to which the resonant frequency of the wire also gets changed. For instance, as the pressure is increased, the element increases the tension in the wire, thus raising its resonant frequency. A digital counter circuit is used to detect the shift. Since this change in frequency can be detected accurately to a certain extent, this type of transducer can be employed for low differential pressure applications as well as to detect absolute and gauge pressures.

Main Features

Resonant wire transducers are specifically designed to detect following pressure ranges:

  • absolute pressures starting from 10 mm Hg,
  • differential pressures up to 750 in. water,
  • and gauge pressures up to 6,000 psig (42 MPa)

Usually, accuracy of a resonant wire pressure transducer is 0.1% of its calibrated span, alongwith a six-month drift of 0.1% and a temperature effect of 0.2% per 1000¡ F.

Advantages

The most momentous advantage of the resonant wire pressure transducer is that it produces an inherently digital output signal, and hence can be sent directly to a stable crystal clock in a microprocessor. Other advantages of this design include:

  • Good repeatability
  • Stability
  • Accuracy
  • Low hysteresis
  • High resolution
  • Strong output signal


Limitations

Limitations of a resonant-wire pressure transducer consist of:

  • sensitivity to temperature changes,
  • a resultant nonlinear output  and
  • a little sensitivity to shock and vibration

In general, these limitations can be diminished by employing a microprocessor to recompense for nonlinearities as well as ambient and process temperature variations.

Sources

tcomega

Encyclopedia

Google Books