7th Sem

Electrical Engineering Department

Batch – B1 (2014 Batch)

Abhishek Choksi

(140120109005)

Industrial Instrumentation (2170913)

ALA Presentation

On

“Variable Inductance & Capacitance Transducers for pressure Measurement”

Prepared By: Guided By:

Prof. Naveen Sharma

Gandhinagar Institute Of Technology

What is a transducer ?

A transducer is a device which transforms a non-electricalphysical quantity (i.e. temperature, sound or light) into anelectrical signal (i.e. voltage, current, capacity…)

What is its structure

• A transducer is made of three blocks:o Input I/Fo Sensoro Output I/F

VARIABLE-INDUCTANCETRANSDUCERS

• An inductive electromechanical transducer is a transducer which converts the physical motion into the change in inductance.

• Inductive transducers are mainly use for displacement measurement

• In such a Transducer the pressure change causes change in the inductance of the sensing element.

• As the pressure passes through the inlet, it is acting on the movablemagnetic core. It causes in increase in the inductance of the coil. As thepressure applied changes the inductance of the coil changes.

Advantages :

• Maintenance free

• Easy repeatability

• Small in size and weighs less

Disadvantages

• The whole circuit is to be shielded as the accuracy can be affetcedby external magnetic field.

• The displacement may produce vibrations which may affect theperformance of the device.

Capacitive Transducers For Pressure Measurement

• A capacitor consists of two conductors (plates) that are electricallyisolated from one another by a nonconductor (dielectric).

• When the two conductors are at different potentials (voltages), thesystem is capable of storing an electric charge.

• The storage capability of a capacitor is measured in farads.

• The principle of operation of capacitive transducers is based upon theequation for capacitance of a parallel plate capacitor as shown in Fig.

• The Capacitive Pressure transducer is shown in above fig.

• It based on the principle that apacitance is inversely propotional to distance between the plates.

• Hence any change in distance between the plates will change the capacitance.

• The Diaphragm acts as one plate of the capacitor. Pressure is applied to the diaphragm. Due to the pressure applied the distance between the static plate and diaphragm changes as the diaphragm moves to left due to the applied pressure, this determines the capacitance between the plates.

• The Change in pressure can be detected by the variation of capacitance.The capacitance is given as,

Advantages of Capacitive transducers:

Low cost

Less power usage

Good stability

Better speed

Good frequency response

They require very less force to operate

Disadvantages of Capacitive transducers

The performance is severely affected by dirt and contaminants as they change the dielectric constant.

They are sensitive to temperature variations

Metallic parts must be insulated from each other

References

• Sensor one : https://www.sensorsone.com/pressure-transducers/

• Electrical for you : https://www.electrical4u.com/transducer-types-of-transducer/

• Wikipedia

• NPTEL : http://nptel.ac.in/courses/108105064/11

• Industrial Instrumentation by U.S Shah