Working Principle of Pressure Measurement , Application, Installation , Advantage disadvantage , Technical specification, comparison with others
Pressure is probably one of the most commonly measured variables in the power plant. It includes the measurement of steam pressure; feed water pressure, condenser pressure, lubricating oil pressure and many more. Pressure is actually the measurement of force acting on area of surface. We could represent this as P = F / A , The units of measurement are either in pounds per square inch (PSI) in British units or Pascals (Pa) in metric. As one PSI is approximately 7000 Pa, we often use kPa and MPa as units of pressure.
Differential pressure gauges measure the difference between two pressures. They are suitable for the monitoring of filter contamination, for level measurement in closed vessels, for over pressure measurement in clean rooms, for flow measurement of gaseous and liquid media and for the control of pumping plants. In differential pressure gauges, different pressure elements and tube forms are used (diaphragm element, capsule element, Bourdon tube, etc.).
Pressure transmitters are used to measure the pressure or level of industrial liquids and gases. The output is transmitted to a control system. Accurate and stable process measurements ensure the safe, reliable, and profitable operation of your plant.
A pressure transducer, often called a pressure transmitter, is a transducer that converts pressure into an analog electrical signal. Although there are various types of pressure transducers, one of the most common is the straingage base transducer. The conversion of pressure into an electrical signal is achieved by the physical deformation of strain gages
Differential Pressure (DP) transmitters measure the difference between two pressures. They use a reference point called the low-side pressure and compare it to the high-side pressure. Ports in the instrument are marked high-side and low-side. The DP reading can be either negative or positive depending on whether the low-side or high-side is the larger value. A DP transmitter can be used as a gauge pressure transmitter if the low-side is left open to the atmosphere.
Pressure gauges are used for the measurement of relative pressures from 0.6 … 7,000 bar. They are classified as mechanical pressure measuring instruments, and thus operate without any electrical power.Bourdon tubes are radially formed tubes with an oval cross-section. The pressure of the measuring medium acts on the inside of the tube and produces a motion in the non-clamped end of the tube. This motion is the measure of the pressure and is indicated via the movement.The C-shaped Bourdon tubes, formed into an angle of approx. 250°, can be used for pressures up to 60 bar. For higher pressures.
Bellows are made of springy metal formed in the shape of thin wall tubes. The tube is then shaped to form deep convolutions,which enable the element to expand in much the same manner as anaccordion. The bellows are sealed on the free end; pressure is applied toan opening on the stationary end. Pressure applied to the inside acts on the inner surface, producing a force that causes the bellows to expandin length, thus producing movement at the free end.
Diaphragms used for very low pressure measurement ranges are usually made of soft, pliable material, either metallic or fibrous. This type of pressure element is sensitive to very little pressure and can be used to measure full-range pressure values as low as 5 to 10 inches of water. The increased sensitivity of diaphragm pressure elements is attributable to the large surface area of the element. It should be remembered from previous discussions that force is equal to pressure times area (F = PA).The force exerted by a pressure
The helical elements produce more free-end traveland torque than spiral elements. Other advantages include a higherrange of operating pressure with sufficient overrange protection. Theoperating range is affected by coil diameter, wall thickness, thenumber of coils used, and the material of construction, which is thesame as may be used in C-tube elements . Applications ofhelical elements include direct reading for the following: indicators,recorders, controllers, switches, transmitters.