Transcript TRANSDUCERS - 123seminarsonly.com

SENSORS MEETING THE NEEDS OF THE DAY
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A device which converts energy or information
in one form to another
In other words, a device which provides a
usable output in response a to specific input
measurand which may be physical or
mechanical quantity ,property or condition.
Basic requirements
of a transducers
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The main function of a
transducer is to respond
only for the
measurement under
specified limits for
which it is designed.
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RUGGEDNESS (Capability of
withstanding overload)
LINEARITY (input – output
characteristics should be linear)
REPEATABILITY (should reproduce
same output signal when the same input
signal is applied again and again)
HIGH OUTPUT SIGNAL QUALITY
(quality of output signal should be
good)
HIGH RELIABILITY & STABILITY
GOOD DYNAMIC RESPONSE (output
should be faithful to input when taken
as a function of time)
NO HYSTERESIS (should not give any
hysteresis during measurement)
RESIDUAL DEFORMATION (should
be no deformation on removal of local
after long period of application)
1: PRIMARY AND
SECONDARY
TRANSDUCERS
2: ACTIVE AND PASSIVE
TRANSDUCERS
3: ANALOG AND
DIGITAL
TRANSDUCERS
4: TRANSDUCERS AND
INVERSE
TRANSDUCERS (An inverse
transducer is a device which that converts an
electrical quantity into a non-electrical quantity)
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RESISTIVE PRESSURE DISPLACEMENT TRANSDUCER
It is used to sense position of an object or the distance it has moved.
The physical variable being measured is made to cause a resistance change in
sensing element.
A resistance element AB with a sliding contact or shaft(w)
linked with the object being monitored.
Resistance between W and B ,R depends on the position of shaft .L1/L XR = R2.
Output voltage V is fn of shaft position
V=V X R2/R1+R2.
ADVANTAGES
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Electrical efficiency high
Provides sufficient output for control operations.
Device may be excited by ac or dc supply.
DISADVANTAGES
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Mechanical friction between W and resistive elements
AB reduces its life.
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RESISTIVE PRESSURE TRANSDUCER
INDUCTIVE PRESSURE TRANSDUCER
CAPACITIVE PRESSURE TRANSDUCER
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It is based on an arrangement in which a change
in pressure results in the
change of the resistance
of a sensing element .
When applied pressure
changes, the spring
bellow extends or
contracts thereby moving
the resistance slider up
and down.Consequently
changes in resistance of
sensing resistive element
become proportional to
the changes in pressure .
INDUCTIVE PRESSURE TRANSDUCER
In
this case, change in
pressure produces a change
in the self inductance of a
sensing element.
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When pressure being
measured increases, the
bellow expands and, hence,
the movable magnetic core
is pushed more inside the
coil thereby increasing in
self inductance. Similarly,
when applied pressure
decreases, the bellows
contract and thus the
magnetic core is pulled out
of the coil and, as a result,
coil inductance is decrease.
The changes in self inductance
can be made a part of an
inductance bridge and
converted into an electrical
signal for pressure
measurement .
As compared to the previous
resistive arrangement the
advantages of this inductive
type are as under :
No moving parts are used thereby
avoiding wear & tear,
No extra friction load is imposed on
the measuring system.
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CAPACITIVE PRESSURE TRANSDUCER
In this arrangement, changes
in pressure are detected by
the variation in the
capacitance of a parallel
plate capacitor whose one
plate is free to move with
change in pressure.
The capacitance of the
capacitor is given by
C=εA/d, where A=plate
area, d= plate separation
When pressure increases the
moving plate comes inwards,
thereby decreasing d and
consequently increasing C.
However when the pressure
decreases exactly opposite
happens. The changes in
capacitance can be used for
pressure determination
ADVANTAGES:
Inexpensive and easy to construct.
Particularly effective for high frequency variations.
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Capable of measuring both static and dynamic phenomena.
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DISADVANTAGES:
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Sensitivity to temperature variation.
Possibility of erratic or distorted signals due to long leads.
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It is an inductive transducer (active) that utilizes the basic
generator principle that when there is any relative motion
between a conductor and a magnetic field or flux , an emf is
induced in the conductor.
The relative motion between flux and conductor is provided in
tachometer by the physical quantity under measurement(velocity).
The object whose angular velocity is to be measured is directly
coupled to the rotor made of permanent magnet having N and S
poles.
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As the rotor rotates , its
alternating flux cuts the
stationary coils thereby
inducing an alternating
voltage ‘E’ in them. The
magnitude of ‘E’ depends on
the angular velocity of the
rotor directly. Polarity of
output voltage indicates
direction of rotation.
This emf can be measured
by using a moving coil
voltmeter having a uniform
scale calibrated directly in
terms of rpm(speed).