1. SVMIT ELECTRICAL Prepared By : - Rohan Kapadia (016)
Bhargav Khambhata (017)
Pradeep Malaviya (018)
Hemik Patel (019)
Snehal Mistry (020)

2. Displacement Transducer
LVDT & RVDT

3. Transducer
A transducer is a device that convert one form of energy to other form. It converts the measurand to a usable electrical signal.
In other word it is a device that is capable of converting the physical quantity into a proportional electrical quantity such as voltage or current.
The physical quantity to be measured can be temperature, pressure, displacement ,flow,vibration etc.
Input Output
Transducer
Pressure
(Physical quantity)
Voltage
(electrical quantity)

4. Classification Transducers Capacitive
On The Basis of
principle Used
Active/Passive
Primary/Secondary
Analog/Digital
Capacitive
Inductive
Resistive
Transducers/
Inverse Transducers
Transducers may be classified according to their application, method of energy conversion, nature of the output signal, and so on.

5. Classification based on displacement
Transducers
Temperature
Transducers
Pressure
Transducers
Displacement
Transducers
Flow Transducers
Others

6. Displacement Measurements
Used to measure directly and indirectly the size, shape, and position of the organs.
Displacement measurements can be made using sensors designed to exhibit a resistive, inductive, capacitive or piezoelectric change as a function of changes in position.

7. Displacement Transducers
A measuring transducer that converts a linear or angular displacemen-t into an electric, mechanical, pneumatic, or other signal suitable for recording, longdistance transmission, or further conversion.
For linear measurement we can use LVDT (Linear Variable Displacement Transducer/ Linear Variable Differential Transformer). and for rotary measurement we can use RVDT (Rotary Variable Differential Transformer)

8. LVDT :- Linear Variable Displacement Transducers/Transformers
Electromechanical transducer
Coupled to any type of object/structure
Converts the rectilinear motion of an object into a corresponding electrical signal
Measures Displacement !!!!!!!!
The linear variable differential transformer (LVDT) is an Inductive variable type displacement transducer.
Liner variable differential transformer excitation to such devices is normally a sinusoidal voltage of amplitude 3 to 15 rms and frequency of 60 to 20,000Hz.

9. Principle
It works on the phenomenon of electromagnetic induction.

10. Construction
It consists of a primary coil and secondary coil all in linear arrangement, with a magnetic core free to move inside the coils. The core is normally made of nickel iron alloy and has longitudinal slot as shown in figure to reduce eddy current .
When core slides through transformer, a certain number of coils are affected.
This generates a unique voltage .

11. How Does An LVDT Work?
This figure illustrates what happens when the LVDT's core is in different axial positions. The LVDT's primary winding, P, is energized by an AC source of constant amplitude. The magnetic flux thus developed is coupled by the core to the adjacent secondary windings, S1 and S2.

12. If the core is located midway between S1 and S2, equal flux is coupled to each secondary so the voltages, E1 and E2, induced in each winding are equal. At this midway core position, referred to as the null point, the differential voltage output, (E1 - E2) is zero.
As shown here, if the core is moved closer to S1 than to S2 , more flux is coupled to S1 and less to S2, so the induced voltage E1 is increased while E2 is decreased, resulting in the differential voltage (E1 - E2). Conversely, if the core is moved closer to S2, more flux is coupled to S2 and less to S1, so E2 is increased as E1 is decreased, resulting in the differential voltage (E2 - E1).

13. The phase angle of this AC output voltage, Eout, referenced to the primary excitation voltage, stays constant until the center of the core passes the null point, where the phase angle changes abruptly by 180 degrees, as shown graphically in this diagram.
This 180 degree phase shift can be used to determine the direction of the core from the null point by means of appropriate circuitry. As this diagram shows, the polarity of the output signal represents the core's positional relationship to the null point.

14. Graphical representation

15. Features !!! Friction – Free Operation Infinite Resolution
NO mechanical contact between core and coil (usually).
Infinite Mechanical Life
Infinite Resolution
Electromagnetic coupling
Limited only by electrical noise.
Low risk of damage
Most LVDT’s have open bore holes.
Null Point Repeatability
Zero displacement can be measured.
Single Axis Sensitivity
Effects of other axes are not felt on the axis of interest.
Environmentally Robust
Stable/Strong sensors – good for structural engineering tests!!!

16. Types Free Core ADVANTAGES :- Generally Less Expensive
Frictionless Operation Possible
Mechanically Coupled Core
ADVANTAGES :-
Generally Less Expensive
Many Ranges and Sizes to Choose
More Complicated to Install
Guided Core
Bearings with Friction, Stiction, etc.
Spring- or Air-Loaded Core
ADVANTAGES :-
Usually Simpler to Install
Perceived as More Expensive
More Limited Selection of Ranges and Limited to Short Strokes

17. Uses Automation Machinery Civil/Structural Engineering
Power Generation
Manufacturing
Metal Stamping/Forming
Pulp and Paper
Industrial Valves
R & D and Tests
Automotive Racing

18. RVDT:-Rotary Variable Differential Transformer
It is a type of electrical transformer used for measuring angular displacement.
It is an electromechanical transducer that provides a variable alternating current (AC) output voltage that is linearly proportional to the angular displacement of its input shaft. When energized with a fixed AC source, the output signal is linear within a specified range over the angular displacement.
(RVDT) is used to measure rotational angles and operates under the same principles as the LVDT sensor. Whereas the LVDT uses a cylindrical iron core, the RVDT uses a rotary ferromagnetic core.  

19. The difference gives a proportional voltage :-
The two induced voltages of the secondary windings,    and  ,
vary linearly to the mechanical angle of the rotor, θ:
Where G is the gain or sensitivity.
The second voltage can be reverse determined by:
The difference   gives a proportional voltage :-
and the sum of the voltages is a constant:

20. This constant gives the RVDT great stability of the angular information, independence of the input voltage or frequency, or temperature, and enables it to also detect a malfunction.

21. Advantages Disadvantages Relative low cost due to its popularity.
Solid and robust, capable of working in a wide variety of environments
No friction resistance, since the iron core does not contact the transformer coils, resulting in an very long service life.
High signal to noise ratio and low output impedance.
Negligible hysteresis.
 Infinitesimal theoretical resolution. In reality, angle resolution is limited by the resolution of the amplifiers and voltage meters used to process the output signal.
 No permanent damage to the RVDT if measurements exceed the designed range.
Disadvantages
  The core must be in contact (directly or indirectly) with the measured surface which is not always possible or desirable.

22. Uses Tachometers Magnetic speed sensors Optical decoders
Variable reluctance tachometers
Accelerometers
Eddy-current tachometers etc.

23. Thank you…!!!