Displacement Measurements

Displacement Measurement

These types of transducers are used to measure small displacements. Normally there are two types of Displacement Transducers: contact and noncontact types. Besides the measurement principles can be classified into two categories: electrical sensing and optical sensing. In electrical sensing, passive electrical sensors are used variation of either inductance or capacitance with displacement is measured. On the other hand the optical method mainly works on the principle of intensity variation of light with distance. Interferometric technique is also used for measurement of very small displacement in order of nanometers. But this technique is more suitable for laboratory purpose, not very useful for industrial applications.

Here I am explaining about contact type displacement measuring equipments. The commonly used types are:

Resistive Types:

·        Potentiometer

Inductive Types:

·        LVDT

·        RVDT

·        Resolver

Capacitive Type:

·        Rotary Type Capacitive transducer

·        Linear Type Capacitive Transducer

Potentiometer

Potentiometers are simplest type of displacement sensors. They can be used for linear as well as angular displacement measurement, as shown in Fig. 1. They are the resistive type of transducers and the output voltage is proportional to the displacement and is given by:

E0= (Xi/Xt)E ,

Where X_i is the input displacement, X_t is the total displacement and E is the supply voltage.

The major problem with potentiometers is the contact problem resulting out of wear and tear between the moving and the fixed parts. Because of friction and moving parts, we can’t expect an accurate measurement. But for simple applications potentiometers are very useful and are of low cost.