Figure 4.6 a) U-tube Manometer b) Well-type Manometer (a) (b)
A device used for balancing a fluid pressure with
a known weight
Typically used for static calibration of pressure gauge
and seldom employed for actual measurement.
[refer figure 4.7]
Architecture and operation:
- The apparatus set-up for calibration of the pressure
- The chamber and cylinderof the tester are filled with
a clean oil by first moving the plunger to its most
forward position and then slowly withdrawing it while
the oil is poured in through the opening for the piston.
Figure 4.7 Dead Weight Tester
- The gauge to be tested is installed and the piston is inserted in the cylinder. - The pressure exerted on the fluid by the piston is now transmitted to the gauge when valve is opened. - This pressure may be varied by adding weights to the piston or by using different piston-cylinder combinations of varying areas. - The viscous friction between the piston and the cylinder in the axial direction may be substantially reduced by rotating the piston-weight assembly while measurement is taken
3) Bourdon-Tube Pressure
Used in many applications because of its consistency,
And inexpensive measurement of static pressure
Commercially available in many sizes (1-to-16 in
diameter) and accuracies.
The heise gauge is an extremely accurate bourdon-tube
gauge with an accuracy of 0.1% of full-scale reading
and it is employ as a secondary pressure standard in
The construction of the bourdon-tube gauge is shown
in figure 4.8
The bourdon-tube itself is usually an elliptical
cross-sectional tube having “C” shape configuration
- When the pressure is applied to the inside of the tube
an elastic deformation results which ideally is
proportional to the pressure.
- The degree of linearity depends on the quality of the
- The end of gauge is connected to a spring-loaded
linkage which amplifies the displacement and transform
it to an angular rotation of the pointer.
Figure 4.8 Bourdon Tube
- The linkage is constructed so that the mechanism may be adjusted for optimum linearity and minimum hysteresis as well as compensate for wear which may develop over a period of time. - An electrical-resistance strain gauge may also be installed on the bourdon-tube to sense thr elastic deformation.
4) Diaphragm and Bellows Gauges
Represent similar types of elastic deformation
devices useful for pressure measurement applications.
Architecture and operation:
- Consider first the flat diaphragm subjected
to the differential pressure p1-p2 as shown in
- The diaphragm will be deflected in accordance with
this pressure differential and the deflection sensed
an appropriate displacement transducer.
- Various types of diaphragm gauge are shown figure 4.10
Figure 4.9 (a) Diaphragm and (b) Bellows (a) (b)
- The bellows gauge is shown in figure 4.9(b).
- A differential gauge pressure force causes displacement
of the bellows, which may be converted to an electrical
signal or undergo a mechanical amplification to
permit display of the output on an indicator dial.
- Figure 4.10 shows various types of bellows gauges.
The bellows gauge is generally unsuitable for transient
measurements because of the larger relative motion and
The diaphragm gauge which may be quite stiff, involves
rather small displacements and is suit for high frequency