Fluid Pressure Sensors

FLUID SENSORS

FLUID PRESSURE SENSORS:

Diaphragm Type:

In the diaphragm type sensor, when there is a difference in pressure between the two sides then the centre of the diaphragm becomes displaced.

Corrugations in the diaphragm result in a greater sensitivity.

This movement can be monitored by some form of displacement sensor, e.g: a strain gauge.

A specially designed strain gauge is often used, consisting of four strain gauges with two measuring the strain in a circumferential direction while two measure strains in a radial

direction

The four strain gauges are then connected to form the arm of a Wheatstone bridge.

While strain gauges can be stuck on a diaphragm, an alternative is to create a silicon diaphragm with the strain gauges as specially doped areas of the diaphragm.

Capsule and Bellow Types:

Capsules are two corrugated diaphragms combined to give greater accuracy

Capsules and bellows are made up of stainless steel, phosphor bronze, and nickel with rubber

and nylon

Pressure range 10³ to 10⁸ Pa

Tube Pressure Sensor:

A different form of deformation is obtained using a tube with an elliptical cross section

Increase in pressure in tube causes it tend to circular cross – section

C – Shaped tube is generally known as a Bourdon tube.

C opens when pressure in the tube increases

A helical form gives more sensitivity

Tubes are made up of stainless steel, phosphor bronze, and nickel with rubber and nylon

Pressure range 10³ to 10⁸ Pa

Piezoelectric Sensors:

Piezoelectric materials when stretched or compressed generate electric charges with one face of the managerial becoming positively charged and the opposite face negatively

charged.

As a result a voltage is produced. The net charge q on a surface is proportional to the amount x by which the charges have been displaced, and since the displacement is

proportional to the applied force F. q =kx= SF

Where k is a constant and S a constant termed the charge sensitivity

Tactile Sensor:

It is used on fingertips of robot hands and for touch display screen

It uses piezoelectric polyvinylidene fluoride (PVDF) film

Two layers are separated by sift film

The lower PVDF film has an alternating  voltage applied to it results in mechanicaloscillations

Intermediate film transmits the vibration to upper film