This transducer is used for displacement measurement. It is done by calculating the change in inductance in a single coil according to the variation in inductance. A schematic of the linear motion variable inductance transducer is shown below.

Working

The device consists of an arm that moves linearly according to the displacement produced. It also consists of a single coil wound on a former with ‘N’ number of turns. The end of the arm is connected to a soft iron core which moves linearly along the axis of the former. Thus, reluctance ‘R’ will be produced due to the flux path. The coil inductance of the device can be written by the equation, L= N² /R.

A linear movement of the arm to the right decreases the reluctance ‘R’ of the flux path. Thus, according to the equation given above, the inductance increases due to the decrease in reluctance and vice versa. This inductance ‘L’ can be calculated or recorded with the help of an inductance bridge or through a recorder. Thus the measure of the displacement of the arm can be obtained from the corresponding change in inductance.
If the transducer is connected to the input of an oscillator tank circuit, the change in frequency ‘f’ of the oscillator could be taken as the measurement for the corresponding change in the displacement of the arm. A displacement of the arm changes the inductance and hence the frequency. Thus, the output can be measured in terms of inductance and frequency.

Advantages

1. There will not be problems due to mechanical hysteresis.

2. Provides a good response to static as well as dynamic measurements.

3. Provides a high output.

Disadvantages

1. The frequency response is controlled by the construction of force ring members.

2. Accuracy errors may occur due to the interference of external magnetic field.