LVDT - Linear Variable Differential Transformer

LVDT is a positive or magnetic displacement transducer; it is commonly used to measure force, weight, pressure and acceleration which depend on force in terms of amount and direction of displacement.

LVDT consist of one primary winding and two secondary windings, which are placed at either side of the primary winding on the same magnetic core as shown in figure. The magnetic core is free to move inside the coil and the motion of core measured the quantity of force or weight. The two secondary S1 and S2 have equal number of turns but are connected in series and opposite, so the e.m.f induces in these windings are 108° out of phase with each other and hence cancel the effect of each other. The induce voltages E1 and E2 in the two secondary windings are equal but opposite in direction as shown in figure.

LVDT - Linear Variable Differential Transformer

Operation / Working of LVDT

When the core is in center of secondary winding, S1 and S2, The induced e.m.f E1 and E2 will be equal but will be opposite in polarity, hence they cancel each other and the net voltage is become zero.

When the external applied force moved the core down word the induce voltage E2 in secondary coil S2 increased but the induce voltage in S1 is decreased in magnitude , they are still out of phase due to which there is some net voltage are induce at out put terminals A and B, whose magnitude is E2 – E1.

When the magnetic core moves up word the induced voltage in secondary winding S1 is increased while the voltage in S2 are decreased and the net output voltage E1 – E2.

Advantages of LVDT

Some of the advantages of LVDT are given below.

  • It gives higher output for small change in magnetic core position.
  • It is highly sensitive transducer which can be used form the range of 50mv/mm to 300mv/mm.
  • It can operate over a temperature range from -650C° to 600C°.

Application of LVDT

These are some main applications of the LVDT.

  • It is used to control the jet engine in aircrafts
  • It is used for the measurement of the thickness and weight in the steel mils.
  • It is used for the measurement of the weight on the highways.