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PRESSURE SENSORS

PRESSURE SENSORS. Fluid Pressure measurement. Bellows Pressure sensor Diaphragm Pressure Sensor Piston Pressure Sensor Bourdon Tube Pressure sensor Solid State Pressure sensor. Pressure Scale. Pressure in a fluid.

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PRESSURE SENSORS

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  1. PRESSURE SENSORS Prepared by Dr. Mohamed Ahmed Awad

  2. Fluid Pressure measurement Bellows Pressure sensor Diaphragm Pressure Sensor Piston Pressure Sensor Bourdon Tube Pressure sensor Solid State Pressure sensor Prepared by Dr. Mohamed Ahmed Awad

  3. Pressure Scale Prepared by Dr. Mohamed Ahmed Awad

  4. Pressure in a fluid • To measure the pressure inside a fluid, imagine introducing a sensor in the form of a tiny evacuated cylinder, with a piston at one end supported by a spring. Prepared by Dr. Mohamed Ahmed Awad

  5. Bellows Pressure sensor Prepared by Dr. Mohamed Ahmed Awad

  6. Bellows Pressure sensor • The most conventional sensitive element used in our pressure and temperature switches is a metallic bellows (bronze or stainless steel) made up of a corrugated tube fitted with two airtight rigid ends. Flexible by nature, it compresses or elongates axially under the effect of pressure and provides excellent transmission. Prepared by Dr. Mohamed Ahmed Awad

  7. Bellows Gauges Prepared by Dr. Mohamed Ahmed Awad

  8. Effective at low pressure up to 100 PSI • Made from metallic material for high pressure. • Reliable, long life • It may act directly on a valve eliminating the need for a switch Prepared by Dr. Mohamed Ahmed Awad

  9. Diaphragm Pressure Gage • The Diaphragm Pressure Gage uses the elastic deformation of a diaphragm (i.e. membrane) instead of a liquid level to measure the difference between an unknown pressure and a reference pressure • A typical Diaphragm pressure gage contains a capsule divided by a diaphragm, as shown in the schematic. One side of the diaphragm is open to the external targeted pressure, and the other side is connected to a known pressure, The pressure difference, mechanically deflects the diaphragm Prepared by Dr. Mohamed Ahmed Awad

  10. Diaphragm :For low pressure, bellows which are too rigid are replaced by an elastomer diaphragm which is hold in place by two metal plates. "Diaphragm" technology is also used in cases of excessively high pressure and pulsating phenomena Prepared by Dr. Mohamed Ahmed Awad

  11. Diaphragm Pressure Gage Prepared by Dr. Mohamed Ahmed Awad

  12. Diaphragm Pressure Gage Prepared by Dr. Mohamed Ahmed Awad

  13. CapsuleTo increases sensitivity Prepared by Dr. Mohamed Ahmed Awad

  14. Diaphragm Pressure Gage • Pros • Much faster frequency response than U tube • High Accuracy • Good linearity • Stand for higher pressure 150 PSI • Cons • Less sensitive than bellows. • More expensive than other pressure sensors Prepared by Dr. Mohamed Ahmed Awad

  15. Piston Pressure Sensor Prepared by Dr. Mohamed Ahmed Awad

  16. This is diagram of a sensor for measuring pressure inside a fluid. • The fluid exerts a force along the axis of the piston, causing it to compress. • The ratio of the force to the area of the piston defines the pressure. • The compression of the calibrated spring indicates the magnitude of the force exerted along the axis of the piston by the fluid. Prepared by Dr. Mohamed Ahmed Awad

  17. Pros and Cons • Pros • Can measure pressure up to 20,000 PSI • Provide reliable operation over Long life • Cons • Has lower accuracy Prepared by Dr. Mohamed Ahmed Awad

  18. Bourdon Tube Prepared by Dr. Mohamed Ahmed Awad

  19. Bourdon Tube Pressure sensor • It is widely used when inexpensive static pressure measurement are needed • It is the most used of all mechanical sensors. • A typical Bourdon tube contains a curved tube that is open to external pressure input on one end and is coupled mechanically to an indicating needle on the other end, as shown • When Pressure increased, the shape of the curved will be straightens. • Most direct reading dial type are Bourdon tube Prepared by Dr. Mohamed Ahmed Awad

  20. Bourdon Tube Pressure sensor Prepared by Dr. Mohamed Ahmed Awad

  21. Bourdon Tube Pressure sensor Prepared by Dr. Mohamed Ahmed Awad

  22. Bourdon Tube Gauge Prepared by Dr. Mohamed Ahmed Awad

  23. Bourdon Tubes Prepared by Dr. Mohamed Ahmed Awad

  24. Bourdon Tube Pressure sensor • Pros • Portable • Convenient • No Leveling required • Can stand for high pressure up to 18,000 PSI • Cons • Limited to static measurement • Accuracy may be insufficient for many applications Prepared by Dr. Mohamed Ahmed Awad

  25. Solid State Pressure sensor • Many pressure sensors used in medical applications are made with piezoresistive semiconductor technology and are therefore considered solid-state devices. • It produces a voltage output that is fairly linearly dependent on the applied pressure. Prepared by Dr. Mohamed Ahmed Awad

  26. Piezoresistance • A piezoresistor is basically a device which exhibits a change in resistance when it is strained. • There are two components of the piezoresistive effect in most materials - the geometric component and the resistive component • The geometric component of piezoresistivity basically comes from the fact that a strained element undergoes a change in dimension. • These changes in cross sectional area and length affect the resistance of the device. • More Information about piezo effect Prepared by Dr. Mohamed Ahmed Awad

  27. Prepared by Dr. Mohamed Ahmed Awad

  28. Piezoresistive Cantilever Prepared by Dr. Mohamed Ahmed Awad

  29. Cross section in Solid state Prepared by Dr. Mohamed Ahmed Awad

  30. What is a Strain Gage A Strain gage is a sensor whose resistance varies with applied force; It converts force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured Prepared by Dr. Mohamed Ahmed Awad

  31. Strain gauge Prepared by Dr. Mohamed Ahmed Awad

  32. 1.                  Resistance •                  Increased resistance •                     heating wire resistor •                   cooling semiconductor •                 stretching (making longer & thinner) wire resistor •                  ‘Strain gauge’: used in pressure transducer •                  To monitor & measure the change in resistance — use of ‘Wheatstone Bridge’ circuit Prepared by Dr. Mohamed Ahmed Awad

  33. Typical Strain gauge Prepared by Dr. Mohamed Ahmed Awad

  34. Strain gauge Prepared by Dr. Mohamed Ahmed Awad

  35. As pressure is applied to the strain gauge, the wires increase in length and decrease in diameter, increasing the resistance to flow of current through the wires of the Wheatstone Bridge •                  This change in the wires electrical resistance causes a voltage change that can be quantified to reflect the amount of pressure that changed the wires length & diameter. •                   The electrical signal can be amplified & measured; when calibrated, it is proportional to the pressure change •                  By combining strain gauge elements of which some stretch while others simultaneously compress, exaggeration of the signal within the Wheatstone bridge can be achieved Prepared by Dr. Mohamed Ahmed Awad

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