Fibre-optic sensors provide an alternative method of measuring displacements in diaphragm and Bourdon tube pressure sensors by optoelectronic means and enable the resulting sensors to have lower mass and size compared with sensors in which the displacement is measured by other methods.
Light rays are sent through an optical fibre to sense the movement of the diaphragm. The light reflects from the diaphragm and the incident light are studied There is a characteristic relationship between the light reflected and the distance from the fibre ends to the diaphragm.
The external unknown pressure is given to the diaphragm. The diaphragm expands and contracts as the pressure increases and decreases. The displacement of the diaphragm is measured by the Fotonic sensor.
Fotonic sensor in which light travels from a light source, down an optical fibre, is reflected back from a diaphragm, and then travels back along a second fibre to a photodetector. There is a characteristic relationship between the light reflected and the distance from the fibre ends to the diaphragm, thus making the amount of reflected light dependent upon the diaphragm displacement and hence the measured pressure.
Apart from the mass and size advantages of fibre-optic displacement sensors, the output signal is immune to electromagnetic noise. However, the measurement accuracy is usually inferior to that provided by alternative displacement sensors, and choice of such sensors also incurs a cost penalty.
Sensors using fibre optics to measure diaphragm or Bourdon tube displacement tend to be limited to applications where their small size, low mass and immunity to electromagnetic noise are particularly advantageous.
- Immune to electromagnetic noise
- Small in size
- Can be used as a secondary sensor to the diaphragm, capacitive sensors, LVDT etc.
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