There are six primary pressure sensor technologies used to sense pressure
1. Potentiometric pressure sensor
Potentiometric pressure sensor uses a bourdon tube capsule or bellows as a pressure sensing element which drives a wiper arm providing pressure measurement values. Using the principle of variable resistance, the movement of the wiper across resistive elements will provide a voltage that is proportional to applied pressure. Bellows are used for sensing pressure. The wiper is mechanically linked with the bellows. Whenever pressure is increased, Bellow expands causing the wiper to upward. This will give more output and reducing resistance. Thus, the output voltage is proportional to the pressure applied. The advantages of potentiometers are simplicity, low cost, adaptability to many applications, and high output signal level. Their disadvantages consist of high hysteresis due to sliding friction, sensitivity to vibration, and finite lifetime associated with wiping elements.
2.Capacitive pressure sensor
A capacitive pressure sensor converts pressure into electrical quantity using a change in capacitance. It uses a diaphragm that is deflected by applied pressure which results in a change in the capacitance value can then be calibrated to provide pressure reading. A Capacitive pressure sensor contains a capacitor with one static plate and one flexible membrane. The area of these plates’ fixed capacitance is proportional to the distance between the plates. It uses a thin diaphragm as one plate of the capacitor. Applied pressures cause the diaphragm to deflect and the capacitance to change. The pressure to measure is applied to the flexible membrane side and the resulting deflection causes a change in capacitance that can be measured using an electrical circuit.
3.Inductive pressure sensor
An inductive pressure sensor uses a linear variable differential transformer (LVDT) to vary the degree of inductive coupling that occurs between the primary and secondary coil of the transformer. The transformer core is connected to the center of the capsule. The movement of the capsule of a pressure sensor can be measured using an LVDT. The output voltage depends upon the movement of the core which is connected to the capsule which is sensing the pressure. So as the capsule moves, the core moves in and out of the transformer thereby changing the output voltage. There are various benefits of using an Inductive pressure sensor that is it has a longer life, high switching rate, predictable results, and performance. It has some drawbacks that the sensing range of an inductive sensor depends on the type of metal being detected, its shape, its size, and also coil size used in the design. That’s why inductive sensor has distance limitations for sensing.
4.Piezoelectric pressure sensor
The piezoelectric pressure sensor has the ability of the material such as ceramic or quartz to generate an electrical potential when the material is subjected to mechanical stress. The main principle of a piezoelectric sensor is that a force. When applied to the quartz crystal produces electric charges on the crystal surface. The rate of charge of force applied s input. As the charge produced is very small. A charge amplifier is needed to produce an output voltage big enough to be measured. Piezoelectric pressure sensor with a piezoelectric crystal inserted between a solid base and the force summing member. If a force is applied to the pressure port, the same force will fall on the force summing member. Thus, the potential difference will be generated on the crystal due to its property. The voltage produced will be proportional to the magnitude of the applied force.
5.Strain guage pressure sensor
Strain gauge pressure sensors are the most common type of pressure sensor.Strain gauge pressure sensors rely on a measurement of the change in electric resistance of a material when stretched to measure the pressure. Strain gauge elements can be made of metal or semiconducting material. The resistance change in metal Strain gauges is mainly due to the change in geometry of the material. Attaching a strain gauge to a diaphragm results in a device that changes resistance with applied pressure.
6.Variable reluctance pressure sensor
Reluctance is the opposition of current flow that is caused by magnetic circuits. Inductance is the property of a coil of wire to build magnetic flux lines. The amount of inductance in the coil depends on the number of turns of wire in the coil, the amount of current flowing in the wire, the type of core that is placed inside the coil of wire, or the position of the core. An easy way to change the amount of inductance in the coil is to change the position of a movable core inside the coil. The movable core can be attached to the diaphragm. When the pressure moves the diaphragm the core will move and change the amount of inductance in the coil of wire. As the amount of inductance changes, inductive reactance also changes. The change of inductance can be used to change the voltage drop across the inductor or it can be used in an oscillator circuit to change the circuit.
