PRESSURE MEASURING SENSOR
ELASTIC PRESSURE TRANSDUCER
BOURDON TUBE
Bourdon tube pressure gauge is the most frequently used because of its simplicity and rugged construction. Bourdon tubes
mainly works based on the principle of Hooke’s Law of Elasticity stating stress applied will be directly proportional to the strain. In this case the stress shall be pressure applied and strain is the strain is the deformation produced in the
bourdon tube causing the pointer to deflect.
Thus the deflection of the pointer is an effect directly proportional to the pressure applied.
CONSTRUCTION AND WORKING
Bourdon tube consists of a length of thin walled tubing which is flattened on diametrically opposite sides. It thus has two long flat sides and two short round sides and is then rolled into a ‘C’ shape of nearly 2700 arc. The tube is then welded into
socket and this will be the pressure inlet for the indicator. The free end is sealed and is called as
Tip.
The final cross section of the tube is oval in shape and the cross section of the tube tends to get round and the tip bends to straighten out. The movement of this is free and is directly proportional to the difference between the pressure inside and outside the Bourdon tube. Thus the movement will give up the gauge pressure.
In the case of vacuum applications the tube wall tends to get
more flat and the tip moves instead of moving out when pressure is applied.
The tip of a
bourdon tube is attached to an adjustable link which is connected to a lever at right angles to it. The other end of the lever is in the shape of a sector or segment gear. This sector gear meshes into a pinion whose shaft carries the indicating pointer. Thus the movement of the tip of the
bourdon tube is transmitted by means of the tip of the gear and pinion to the pointer. A hair spring
is also made use of to help the pointer return to zero position and thus to remove
back lash error.
RANGE AND MATERIALS FOR BOURDON TUBE
The
bourdon tube type of pressure indicator has a very wide range for which it can be used for pressures as low as 15 PSI and for pressure as high as 80,000 PSI. Different materials can be used for construction for different range of applications. The most commonly used materials are Bronze, Phosphor, Beryllium, Copper, Alloy steel, Monel and stainless steel. Generally Phosphor and Bronze are used and is applicable up to pressures of 600 PSI. Beryllium and Copper are
applicable for high pressures up to the limit of 10,000 PSI and alloy steel is used for
pressures high used when the
bourdon tube is in contact with some corrosive fluid.
SPIRAL TYPE PRESSURE GAUGES
Spiral pressure sensors are the modified form of
bourdon tubes. As the tip travel of the bourdon tube is very small sometimes the free end of the tube is wound several times with the entry for applied pressure at the centre. This increases the total tip movement due to the increase in the total tip movement due to increase in the total tube length and varies with the number of turns of the spiral.
HELICAL TYPE PRESSURE GAUGES
Helical type is also a modified form of the bourdon tube and is named so because the bourdon tube element is shaped into a helical form. It is generally used in the recorder which is used for the pressures of two or more points simultaneously.
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