Pakarab fertilizers limited multan



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Field Instrumentation
a. C shape bourdon tube.
It is used up to ranges from 0 to 10,000 psig. The range depends on material used, flatness of tube and cross sectional area of tube.
b).Spiral tube
Spiral element is actually along C- type tube resembling a flat coil. One end is rigid, and the movement of the free end is linked to a pointer of indicator.
c).Helical tube
Helical element is along C-type spring wound like a vertical spring. It is more sensitive to small changes.

Bourdon Tube shapes
II.
Diaphragm pressure sensors
A diaphragm is a flexible disk that changes shape as the process pressure changes. Disk is held firmly all around the outer edge. The process pressure pushes on one side of the disk. Central portion of the disk moves in or out as the process pressure changes. Two types of diaphragms are used.


38 Field Instrumentation GEN Rev) Diaphragm pressure sensor
Single diaphragm: uses only one flexible element.
Single diaphragm
Capsule diaphragm: uses two flexible elements.


39 Field Instrumentation GEN Rev) Diaphragm capsule maybe made of phosphor bronze, stainless steel or other metal alloys. Two diaphragms are welded together around the edge to make the capsule. The inside of the diaphragm is then connected to the process pressure and outside pressure is the reference. Outside of the capsule is exposed to the atmosphere (for measuring gauge pressure. Capsule can be enclosed in sealed container so that reference can be either a vacuum or one side of a process pressure. Capsule diaphragm III.
Bellows pressure sensors It is formed from a homogenous piece of seamless tubing. When pressure is applied to one end, the circular sections expand axially and this motion is used as a measure of the pressure. It is usually made of brass or stainless steel. Bellows pressure sensors


40 Field Instrumentation GEN Rev)

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