Experiment – 4

Study of Linear Variable Differential Transformer (L.V.D.T)

Aim: To study linear variable differential transformer (L.V.D.T)

Equipments required:

1) Patch cords2) LVDT trainers kit

Theory:

The L.V.D.T has three solenoidal coils placed end-to-end around a tube. The centre coil is the primary and the two outer coils are the top and bottom secondaries. A cylindrical ferromagnetic core, attached to the object whose position is to be measured, slides along the axis of the tube. An alternating current drives the primary and causes a voltage to be induced in the coil in each secondary proportional to the length of the core linking to the secondary. The frequency is usually in the range 1 to 10 kHz. As the core moves, the primary’s linkage to the two secondary coils changes. The coils re connected so that the output voltage is the difference between the top secondary voltage and bottom secondary voltage. When the core is central in position, equidistant between the two secondaries, equal voltage are induced in the two secondary coils, but the two signals cancel so the output voltage is theoretically zero. In practice minor variations in the way in which the primary is coupled to each secondary means the primary is coupled that a small voltage is output when the core is central.

Procedure:

1) Connect the trainer kit to the mains supply and switch ‘ON’2) Now, slowly shift the position of LVDT. Print A, B and C as per the observe the

null point and phase shift position of the input signal between A and C terminals.

3) Now connect the output of LVDT point A, B and C at LVDT detector circuit with the help of patch cords. Calibrate the output of LVDT to 10 mm by adjusting the output potentiometer of the detector circuit.

4) Connect the LVDT to the displacement indicator digital meter.5) Observe and record the output of LVDT and plot the graph of displacement in

mm v/s output in D.C. millivolts. Verify the linearity of LVDT.

Observations:

Conclusions: