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Pressure measuring devices

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Pressure measuring devices

  1. 1. Deepak kumar
  2. 2. Pressure  Pressure (P) expresses the magnitude of normal force(F) per unit area(A) applied on the surface.  SI units :- Pascal (N/m²)  Other units:- bar(=10⁵ pa),atm (=101.3kpa),  mm of hg or ( torr = 0.133322kpa)
  3. 3. Principle:- The bourdon tube works on a simple principle that a bent tube will change its shape . As pressure is applied internally, the tube straightens and returns to its original form when the pressure is released . The tip of the tube moves with the internal pressure change and is easily converted with a pointer onto a scale.
  4. 4. Advantages:-  Inexpensive Wide operating range  Fast response  Good sensitivity  Direct pressure measurements Disadvantages:- Hysteresis on cycling Sensitive to temperature variations Limited life when subjected to shock and vibrations Applications:- These devices should be used in air if calibrated for air and in liquid if calibrated
  5. 5. Diaphragm Gauge of pressure measurements The diaphragm is a flexible disc, which can be either flat or with concentric corrugations and is made from sheet metal with high tolerance dimensions. The diaphragm can be used as a means of isolating the process fluids, or for high pressure applications. It is also useful in providing pressure measurement with electrical transducers (LVDT). It is used as primary pressure transducers in many dynamic pressure measuring devices.
  6. 6.  Diagram:-
  7. 7.  Types of diaphragms :-
  8. 8. consider, pw= deflection developed due to pressure difference, P(ext.)=applied pressure (measured pressure), P(ref)= atmospheric pressure, a= radius of diaphragm t= thickness, E= young’s modulus, γ= poison’s ratio, Δp= difference in pressure, Now deflection can be given by; 3Δ푝푎⁴(1−γ2) W= 16퐸푡³ {γ for metal= 0.3-0.5) Let k =3a⁴(1-γ²)/ 16Et³, therefore, w= k*Δp
  9. 9. Advantages :- Good for low pressure Inexpensive Wide range Reliable and proven Used to measure gauge, atmospheric and differential pressure.
  10. 10. Linear variable differential transformer(LVDT) This type of pressure measurement relies on the movement of a high permeability core within transformer coils . the movement is transferred from the process medium to the core by use of a diaphragm , bellows or bourdon tube. 
  11. 11. Working principle :-  The LVDT operates on the inductance ratio between the coils. The primary coil is located between two secondary coils and is energized with an alternating current . Equal voltage are induce in the secondary coil if the core is in the center when the core is moved from the center position the result of the voltages in the secondary winding will be different.
  12. 12. Conversion of ac to dc