Displacement is a vector quantity representing a change in position of a body or a point with respect to a reference. It can be linear or angular (rotational) motion.

• With the help of displacement transducer, many other quantities, such as force, stress, pressure, velocity, and acceleration can be found.
• In case of linear displacement, the magnitude of measurement may range from a few micrometers to a few centimetres.

• A majority of displacement transducers detect the static or dynamic displacement by means of suitable mechanical links coupled to the point or body whose displacement is to be measured.

   

The main electrical displacement transducers work on the principle of

1. Variable resistance: transducer is strain gauge.
2. Variable inductance: transducer is linear variable differential transformer
3. Variable capacitance: transducer is parallel plate capacitor with variable gap

4. Synchros and resolvers: used to measure angular displacement.

    

A simple and more popular type of displacement transducer is the variable inductance type wherein the inductance is varied according to the displacement. This is achieved either by varying the mutual inductance between the two coils (linear variable differential transformer) or by varying self inductances (variable reluctance sensor). The very fine resolution, high accuracy, and good stability make LVDT most suitable as a position-measuring device.

LVDT forms the basic sensing element in the measurement of pressure, load, and acceleration. It is also a basic element of electronic comparators, thickness - measuring units, and level indicators.

Displacement Measurement transducers:

• LVDT
• Hall effect transducers for measurement of angular displacement
• Capacitive transducers
• Capacitive pressure transducers
• Resistive displacement transducers
• Precision potentiometers
• Inductive transducers