Introduction of LVDT
LVDT full form is a Linear Variable Differential Transformer. As the name suggests, many people get confused that it is a Transformer. But actually, it is a Transducer, not a
Transformer. Because its working principle is the same as the Transformer (i.e. Mutual Induction Principle) and the output across its secondary coil is in the form of differential voltage, that’s why it is named a Linear Variable Differential Transformer (LVDT). It is categorized as an Inductive Transducer used to measure the speed or position of an object. Generally, most Inductive Sensors work on the principle of a Transformer. Now let’s discuss the complete concepts of LVDT in detail.
What is LVDT?
|Construction of LVDT|
Hydrogen annealing is done on the Iron core to reduce harmonics, and residual voltage of the core and thus provides high sensitivity. The movable core also is laminated in order to reduce the eddy current losses. The displacement to be measured is attached to this movable soft iron core. LVDT is placed inside the stainless steel housing because it will provide electrostatic and electromagnetic shielding.
LVDT Working Principle
|Working of LVDT|
Now according to the position of the core, there are three cases that arise. So Let’s discuss these three cases one by one in detail.
Case 2: When the core is at Null position.
Case 3: When the core moves towards S2 (Max Right).
From all these three cases, we can have the following conclusions:
- The direction of the movement of an object can be identified with the help of the differential output voltage of LVDT. If the output voltage E0 is positive then this means an object is moving towards the Left from the Null position.
- Similarly, If the output voltage E0 is negative then this means the object is moving towards the Right of the Null position.
- The amount or magnitude of displacement is proportional to the differential output of LVDT. The more the output voltage, the more will be the displacement of the object.
- If we take the core out of the former then the net differential of the output of LVDT will be zero.
- In fact corresponding to both cases, whether the core is moving either Left or Right to the Null position. Then the output voltage will be increased linearly up to 5mm from the Null position and after 5 mm output E0 will be non-linear.
Following are the main advantages and disadvantages of using LVDT as a secondary Transducer.
Advantages of LVDT
- Smooth and Wide Range of Operation:- LVDT has a very wide range of measurement of displacement. It can measure displacement ranging from 1.25mm to 250 mm.
- High Sensitivity:- LVDT gives a high output value so that there is no need for any Amplifier circuit for the amplification process. Typically the sensitivity of LVDT is recorded as 40V/mm.
- Low Hysteresis Losses:- LVDT gives low hysteresis losses hence repeatability is excellent under all the conditions.
- Low Friction Losses:- As the core moves in a hollow Former, there is no concept of friction losses. Hence it gives an accurate output value.
- Rugged Operation:- It can tolerate a high degree of shock and variation, especially when the core is loaded with spring.
- Low Power consumption:- LVDT consumes very low power of approx 1W during its operation.
- Direct conversion to Electrical Signal:- They convert linear displacement directly to the corresponding electrical voltage signal which is easy to process further.
- Fast dynamic Response:- Due to the absence of Friction, Its dynamic response becomes very fast to change in a core position.
Disadvantages of LVDT
- Since LVDT is an Inductive Transducer, it is sensitive to a Stray Magnetic Field. Hence an extra setup is required to protect it from Stray Magnetic Fields.
- Since it is an electromagnetic device, it also gets affected by vibrations and temperature variation.
Applications of LVDT
- LVDT is used to measure physical quantities such as Force, Tension, Pressure, Weight, etc. These quantities are first converted into displacement by the use of primary transducers and then it is used to convert the displacement to the corresponding Electrical voltage signal.
- It is mostly used in industries as well as a servomechanism.
- It is also used in Industrial Automation and aircraft. Turbine, Satellite, hydraulics, etc.
- Range of Measurement: ± 0.25 mm to ± 750 mm
- Operating Temperature: (-265 to 600) degree celsius.
- Frequency Range: 50 Hz to 20 kHz.
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