Prepared by Dr. Mohamed Ahmed Awad PRESSURE SENSORS Prepared by Dr. Mohamed Ahmed Awad

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

Prepared by Dr. Mohamed Ahmed Awad Pressure Scale Prepared by Dr. Mohamed Ahmed Awad

Prepared by Dr. Mohamed Ahmed Awad 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. This is diagram of a sensor for measuring pressure inside a fluid. The fluid exerts a force of magnitude along the axis of the piston, causing it to compress. The ratio of to the area A of the piston defines the pressure. The compression of the spring indicates the magnitude of the force exerted along the axis of the piston by the fluid. Then, if the cross-sectional area of the piston is A, and the force acting along the piston’s axis has magnitude , the pressure P is defined to be Prepared by Dr. Mohamed Ahmed Awad

Bellows Pressure sensor Prepared by Dr. Mohamed Ahmed Awad

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

Prepared by Dr. Mohamed Ahmed Awad Bellows Gauges Prepared by Dr. Mohamed Ahmed Awad

Prepared by Dr. Mohamed Ahmed Awad 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

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

Prepared by Dr. Mohamed Ahmed Awad 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

Diaphragm Pressure Gage Prepared by Dr. Mohamed Ahmed Awad

Diaphragm Pressure Gage Prepared by Dr. Mohamed Ahmed Awad

Capsule To increases sensitivity Prepared by Dr. Mohamed Ahmed Awad

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

Piston Pressure Sensor Prepared by Dr. Mohamed Ahmed Awad

Prepared by Dr. Mohamed Ahmed Awad 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

Prepared by Dr. Mohamed Ahmed Awad 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

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

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

Bourdon Tube Pressure sensor Prepared by Dr. Mohamed Ahmed Awad

Bourdon Tube Pressure sensor Prepared by Dr. Mohamed Ahmed Awad

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

Prepared by Dr. Mohamed Ahmed Awad Bourdon Tubes Prepared by Dr. Mohamed Ahmed Awad

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

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

Prepared by Dr. Mohamed Ahmed Awad 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

Prepared by Dr. Mohamed Ahmed Awad

Piezoresistive Cantilever Prepared by Dr. Mohamed Ahmed Awad

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

Prepared by Dr. Mohamed Ahmed Awad 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

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

Prepared by Dr. Mohamed Ahmed Awad 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

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

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

Prepared by Dr. Mohamed Ahmed Awad 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