Download Aim: The goal of this project is to study a Linear variable differential

Aim:
The goal of this project is to study a Linear variable differential transformer (LVDT) , typical
characteristic of measuring devices and possible applications.
Apparatus:
LVDT, micrometer, analog transducer amplifier
Theory
Operating principle: Electromagnetic Induction Whenever the flux linkage through an
electric conductor changes, a voltage is induced in the conductor. In case of LVDT, an object
of ferromagnetic material is moved within the flux path which in effect changes the
reluctance of the flux path and brings about the change in flux linkage. Thus mechanical
energy (used in moving the ferromagnetic material) is directly converted into electrical
energy. The induced voltage is used as a measure of the motion.
Construction:
LVDT consists of a cylindrical, insulating, non-magnetic form that has primary coil in the
mid segment and a secondary coil symmetrically wound in the two end segments. The two
secondary coils are connected in series opposition, so that the potentials induced in the two
coils segments oppose each other. A core of ferromagnetic material is inserted coaxially in
the cylindrical form without actually touching it.
Working:
The primary coil is energized by AC supply voltage. As a result AC voltage of same
frequency is induced in the secondary windings. When the core moves the reluctance of the
flux path changes and hence the flux linkage with two secondary windings changes. Since the
two secondary coils are connected in series opposition, it is seen that the net induced voltage
is zero(Vo = Vs1 - Vs2; Vs1 = Vs2; Vo = 0) when the core is at the centre in between the two
secondary windings. This position is known as ’Null position’. Also, since the secondary
windings are connected in series opposition, the LVDT provides direction as well as
magnitude displacement. At steady state, the amplitude Vo of the induced voltage is
proportional, in the linear region, to the core displacement.
Note: An error known as ’zero error’ is present in some differential transformer i.e. a nonzero reading at the null position. The main reasons for the zero error are non-uniformities in
the windings, harmonic components in the primary signal, and non linearity in the device.
The LVDT is a transducer which converts mechanical energy into electrical energy i.e we get
output in terms of voltage. Transduced energy levels are generally weak and often need
conditioning. The signal conditioning is achieved by analog transducer amplifier which we
connect to the LVDT. The signal conditioning associated with the differential transformers
includes filtering and amplification. Filtering is necessary to reject the noise i.e. to achieve
high signal to noise ratio of the o/p signal .Amplification is necessary to achieve signal
strength for data acquisition and processing.
Applications:
Applications of LVDT are:
 Automotive appliances
 Automotive Test Laboratories
 Die casting machinery
 Fossil fuel and Nuclear Power
 Ground attack vehicles
 Industrial gauging
 Industrial Robots
 Injection Moulding Machinery
 Material handling and testing equipments
 Missiles
 Punch presses and Press brakes
 Simulators
 Space shuttles
 Weighing systems
 Military and Commercial Aircraft
Procedure:
1. Connect the o/p of LVDT to the i/p of Analog Transducer Amplifier.
2. Connect the voltmeter to the o/p of Analog Transducer Amplifier.
3. Adjust the micrometer such that voltmeter shows approximately 0 V dc.
4. Take readings for increasing value of displacements till the o/p becomes constant for any
number of further increments.
5. Similarly take the readings for decreasing value of displacement till the o/p voltage
becomes constant for any number of further decrements.
6. Plot the graph of displacement vs Voltage and observe the linearity.
7. Draw Conclusion.