Download Transducer

SVMIT ELECTRICAL
Prepared By : -
Rohan Kapadia
Bhargav Khambhata
Pradeep Malaviya
Hemik Patel
Snehal Mistry
(016)
(017)
(018)
(019)
(020)
Displacement Transducer
LVDT & RVDT
 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
Pressure
(Physical quantity)
Output
Transducer
Voltage
(electrical quantity)
 Classification
Transducers
On The Basis of
principle Used
Active/Passive
Primary/Secondary
Analog/Digital
Transducers/
Inverse Transducers
Capacitive
 Transducers
Inductive
Resistive
may be classified according to
their application, method of energy
conversion, nature of the output signal, and
so on.
 Classification based on displacement
Transducers
Temperature
Transducers
Pressure
Transducers
Displacement
Transducers
Flow
Transducers
Others
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.
6
 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)
 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.
o Principle
• It works on the phenomenon of electromagnetic induction.

L
i
Where: L= inductance
 = magnetic flux
i = electric current
o 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 .
 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.
 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).
 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.
 Graphical representation


Friction – Free Operation


Zero displacement can be measured.
Single Axis Sensitivity


Most LVDT’s have open bore holes.
Null Point Repeatability


Electromagnetic coupling
 Limited only by electrical noise.
Low risk of damage


NO mechanical contact between core and coil (usually).
 Infinite Mechanical Life
Infinite Resolution


Features !!!
Effects of other axes are not felt on the axis of interest.
Environmentally Robust

Stable/Strong sensors – good for structural engineering tests!!!
 Types
• Free Core
o
o
Frictionless Operation Possible
Mechanically Coupled Core
• Guided Core
o
o
Bearings with Friction, Stiction, etc.
Spring- or Air-Loaded Core
• ADVANTAGES :• Generally Less Expensive
• ADVANTAGES :• Usually Simpler to Install
• Many Ranges and Sizes to
Choose
• Perceived as More
Expensive
• More Complicated to Install
• More Limited Selection of
Ranges and Limited to
Short Strokes
 Uses
•
•
•
•
•
•
•
•
•
Automation Machinery
Civil/Structural Engineering
Power Generation
Manufacturing
Metal Stamping/Forming
Pulp and Paper
Industrial Valves
R & D and Tests
Automotive Racing
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.
 The two induced voltages of the secondary windings,
vary linearly to the mechanical angle of the rotor, θ:
and
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:
,
• 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.
 Advantages
o Relative low cost due to its popularity.
o Solid and robust, capable of working in a wide variety of environments
o No friction resistance, since the iron core does not contact the transformer coils,
resulting in an very long service life.
o High signal to noise ratio and low output impedance.
o Negligible hysteresis.
o Infinitesimal theoretical resolution. In reality, angle resolution is limited by the
resolution of the amplifiers and voltage meters used to process the output signal.
o No permanent damage to the RVDT if measurements exceed the designed range.
 Disadvantages
o The core must be in contact (directly or indirectly) with the measured surface which is
always possible or desirable.
not
 Uses
o Tachometers
o Magnetic speed sensors
o Optical decoders
o Variable reluctance tachometers
o Accelerometers
o Eddy-current tachometers etc.
Thank you…!!!