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RVDT – Rotary Variable Differential Transformer

RVDT (Rotary Variable Differential Transformer) is a passive transducer, that works on the principle of mutual induction. It is used to measure the angular displacement. The design of RVDT is similar to LVDT, except for the design of the core.

Read More: LVDT Construction,Principle and Advantages.

Construction of RVDT

RVDT consists of one primary coil and two secondary coils wounded on a cylindrical core. RVDT uses a cam-type core made up of a ferromagnetic material and it can be twisted among the two windings using the shaft.


The primary winding is connected to an AC source. The two secondary windings S1 and S2 have an equal number of turns and are set up in series opposition.

Operation of RVDT

The working of RVDT is same as LVDT. When an alternating voltage is applied in the primary windings of an RVDT, an emf is induced in the secondary windings.

Suppose V1 is the voltage induced across coil S1 and V2 is the voltage induced across S2. The overall output voltage across the secondary winding(V0) is the difference between V1 and V2.

So the differential output is


Based on the movement of the shaft, following three conditions will be occured.

  • When the core is in the centre position. (NULL Position)
  • When the core rotates in a clockwise direction.
  • When the core rotates in the anti-clockwise direction.

When the core is placed at the centre position, voltages induced across secondary windings are equal although reversed in phase. That is V1=V2. Then, the resultant voltage V0=0.

When the shaft is rotated in the clockwise direction, then more emf is generated in coil S1. That is V1>V2. Here V0 will have a positive value.

Similarly, anti-clockwise rotation of shaft leads to increase in voltage V1. That is V2>V1. Here V0 will have a negative value.

Advantages of RVDT

  • Durable.
  • Low cost.
  • Easy to handle.
  • High accuracy.
  • Long life.
  • Excellent linearity.

Application of RVDT

  • Robotics.
  • Modern machine tools.
  • The fuel control system of engines.
  • Fuel valve as well as hydraulics.
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