ELECTROMECHANICAL PRESSURE SENSORS: This is the type of pressure sensor that converts applied pressure to an electrical signal. The electrical signal (output) provides different uses with different uses for different applications.
POTENTIOMETRIC PRESSURE SENSORS: This sensor works on the basis that pressure changes causes the arm to move back and forth across a potentiometer, and a resistance measurement can be read. It consists of an arm attached to the elastic pressure sensing element. The sensing elements do have a working range, which restricted their resolution by some parameters. Potentiometric pressure sensors are best used as a cheap detector evaluating a coarse process. The pressure range is 0.035 - 70 MPa with a sensitivity of 0.07 -0.35 MPa
A CAPACITIVE SENSOR: This type of sensor is designed to operate within a pressure range of 2.5 Pa - 70MPa with a sensitivity of 0.07 MPa. A capacitive sensor consists of a parallel plate capacitors and an electrode connected to a diaphragm which is exposed to the process pressure on one side and the reference pressure on the other side. Any movement along the diaphragm is detected by the electrode, which lead to change in capacitance. The change of the capacitance is detected by an attached circuit which in turn read the voltage in relationship to pressure change.
PIEZOELECTRIC SENSORS: Piezoelectric sensors use a crystal sensor. When pressure is applied to the crystal, it twists and a small amount of electric charge is created. In this type of pressure sensor change in pressure is proportional to electric charge. The piezoelectric element is very sensitive, and pressure range is0 .021 - 100 MPa with a sensitivity of 0.1 MPa.
RELUCTIVE PRESSURE SENSORS: When there is a change in pressure, the flexible element reacts by moving the ferromagnetic plate, which leads to a change in the magnetic flux of the circuit which can be measured. One of the condition in which reluctive pressure is employed is when the inductive sensor does not generate a precise enough measurement. The pressure range is 250 Pa - 70 MPa with a sensitivity of 0.35 MPa.
STRAIN GAUGE: The strain gauge senses changes in pressure by measuring the change in resistance of a Wheatstone bridge circuit.
The set up in the strain gauge is in a way that sensors are placed on each of the resistors and measures the change in resistance of each individual resistor due to a change in pressure
Resistance is given by the formula where ρ = resistivity of the wire, L = length of the wire,
and A = cross-sectional area of the wire .
source: https://controls.engin.umich.edu/wiki/index.php/PressureSensors