Fluid enters the tube,the tube tends to straight out when pressure is applied.This causes a movement
of the closed end and the displacement of this end is amplified to mechanical linkages.
The amplified displacement of the free end may be use to move a pointer on a scale, calibrated in terms
of pressure or may be applied to electrical whose output calibrated in terms of pressure.
The bourdon tube are made designed in various forms.
- Twisted type
The Bourdon tube are made out of a elliptically flattend bent tube,in such a way as to produce the
shapes shown below.One end of the tube is sealed or closed.The other end is open for the fluid to enter
whose pressure is to be measured.
The C-type of bourdon element is most commonly used for local indication but it is also used for
pressure measurement and control applications.The tube is oval in section and is formed into an arc
of 250° .
This type of tube can be made in the form of a spiral.An increased displacement of the free end can
be obtained by increasing the number of turn in the spiral.
When pressure is to be measured is applied,it tends to uncoil producing a relatively long movement of
the tip whose displacement can be used for indication or transmission.
The accuracy is higher than that C-type bourdon tube.
The displacement of the tip of a helical element is larger than that of spiral element.Usually a control
shaft is installed within a helical element and the pointer is driven from this shaft by connecting links.
The system transmits only the circular motion of the tip to the pointer which is directly proportional to
the changes in pressure.
- Low cost
- Simple construction
- High pressure range
- Good accuracy
- Improved Design
Their greatest advantage is that they are easily adapted for design for obtaining electrical outputs.
Their low spring gradient which their use units for precision measurement upto a pressure of 3 µN/m² are susceptible to shocks and vibrations and are subjected to hysteresis.