1. TRANSDUCER

2. • Transducer is a device that receives energy in
one system and transmits to other in a
different form.
• Will generate signal related to the input
received which energizes the transducer.
• The output may be mechanical or electrical
• The energy transmitted may be mechanical or
electrical or acoustical.
• There are two types- electrical and mechanical

3. Sen
sor
Sensing element Transduction
ele
element Electrical signal
me
nt

4. Parameters of transducer
• Linearity – relationship between input and
output must be linear.
• Dynamic range –should be wide.
• Physical size –minimum weight and volume.
• repeatability- i/p and o/p relationship must be
predictable.
• Accuracy – ideal value of the variable being
measured.
• Physical size – have minimal weight and

5. ELECTRICAL TRANSDUCER
• It converts non electrical signal into electrical
signal.
• The output can be easily used for transmission
and storage.
• Effects of friction are minimized.
• Electrical amplification and attenuation can be
easily done.
• Can be controlled with a very small power
level.

6. • Electrical Transducer is a sensing device
by which a physical , mechanical or optical
quantity to be measured is transformed
directly into electrical voltage or current
proportional to the input.
• Mechanical Transducers respond to change in
physical conditions and give output in
different form.

7. • The output can be modified.
• The output can be recorded at a distance from
the sensing medium.
• It can be classified into two major categories
• Active
• Passive
• Active transducer generates electrical signal in
response to input
• Does not require any power source for operation

8. • Example- piezoelectric cells
• Photovoltaic cells
• Passive transducers depend on the change in
electrical parameters such as R,L,C.
• Examples- strain gauge, thermistors
• Electrical transducers contains sensing
element and transduction element.

9. SELECTION OF TRANSDUCER
• 1.loading effect- should have a minimum
loading effect to keep the errors to minimum.
• Nature of measurement
• Environmental conditions pressure ,shock, size
and mounting restrictions
• Operating range
• Electrical parameters

10. RESISTIVE TRANSDUCER
• Material in which the resistance due to a
change in some physical phenomenon.
• Potentiometer-it consists of a resistance
element provided with a sliding contact called
wiper.
• Movement can be in rotational and
translational or combination of both.

11. • It is a method of converting mechanical
displacement into electrical output.
• The electrical output is proportional to
movement.
• Based on the position of the pot the resistor
will be added.

15. ADVANTAGES
• They are inexpensive
• Simple to operate.
• Disadvantages-large force is required to move
sliding contact
• Can generate noise and misaligned.

16. Resistance pressure transducer
• It is based on the fact that a change in pressure
results in a resistance change in sensing
element.
• The element made by the pressure change is
made to cause a change in resistance.
• The change of resistance can be made part of a
bridge circuit

17. • Fluid or gas whose pressure is to be measured
to pass through pressure sensitive element.
• Causes mechanical displacement.
• Output is proportional to the displacement.
• Bellows is a sensitive element thin walled
cylindrical shells.
• Materials used are phosphor bronze.

20. Strain gauge
• It is an example of passive transducer.
• It uses the variation in electrical resistance in
wires to sense the strain produced by the
force on the wires.
• If a metal conductor is stretched its resistance
changes.
• It is mounted on material which is subjected
to force.

21. Resistance wire gauge
• Unbounded resistance wire gauge and bonded
strain gauge
• In first one a wire is stretched between two
points in an insulating medium
• The diameter is 25 micro meter.
• It is connected to bridge circuit.
• When external load is applied resistance
changes and causes unbalance in bridge
circuit

23. • In bonded strain gauge it's looped back and
forth on a carrier
• The wire is covered on top with a thin material
• A stress tends to change the length of wire
and length increases.
• The strain gauge is normally used in bridge
arrangement.
• Only one of the gauge is active producing the
output proportional to force.

24. Types of strain gauge
• The rosette type is having three or four arms.
• It is used when the direction of force is
unknown
• Gauge elements are arranged in either 45
degree or 60.
• Torque and helical type are the other type of
gauge transducer.
• Advantages.
• It should have a high value of gauge factor.
• The ressitance should be as high as possible.

25. • It should not have hysteresis effect,.
• The variation in resistance should be having
linear characteristics.

30. Foil strain gauge
• The strain is detected using am metal foil.
• The metals and alloys used are nichrome
,constantan etc.
• It is based on peizo resistive effect.
• They can be fabricated on large scale and at
any shape.
• It can be mounted on remote and places and
curved surfaces.
• The resistance values is generally 50 and 1000.

33. Semiconductor strain guage
• These are used when high value of gauge
factor is necessary.
• They have gauge factor 50 times as high as
wire strain gauges.
• Materials used are germanium and silicon.
• It consists of strain material and leads that are
placed in a box.
• Semiconductor wafer which have thickness of
0.05 mm are used.

34. advantages
• It can be used to measure very small strains.
• Very small in size ranging from .7 to 7.0mm
• But they are more expensive and linearity of
these type is poor.

35. RESISTANCE thermometer
• The resistance of a conductor changes when its
temperature is changed.
• It is used to measure the resistance in terms of
temperature.
• Its main part is the sensing element.
• It exhibits a relatively large resistance change
with change in temperature.
• Platinum, nickel, copper are the metals most
commonly used to measure temperature.

37. • The measurement is very accurate.
• It has a lot of flexibility with regard to choice
of measuring equipment.
• Stability of performance over long period of
time.
• But they have higher cost need for bridge
circuit and power source.

38. INDUCTIVE TRANSDUCER
• IT IS A DEVICE WHICH converts physical motion
into change in inductance
• It works on one of the following methods
• Variation of self inductance
• And variation of mutual inductancce.
• It is mainly used for the measuremnt of
diaplacement.
• It is arranged to cause the variations in any one of
the variables
• Number of turns
• Geometric configuration.

41. Variable reluctance type
transducer
• It consists of a coil or winding wound on a a
ferromagnetic core.
• The displacement which is to be measured is
applied to ferromagnetic target.
• The target does not have any contact with he
core on which it is mounted.
• When the target is near the core length is
small and therefore the reluctance is large.

42. • When the target is away from the core the
reluctance is large resulting in smaller self
inductance value.
• Thus the inductance of the coil is a function of
displacement.

44. • In variable reluctance bridge a saperate col is
wound on each outside leg of E core and iron
bar is pivoted on center leg.
• The moving member is attached on one end
of the iron bar.
• It is balanced only when the inductance of the
two transducer coils are equal

46. Thermistor
• Thermistor is as a semiconductor component which
made by pure oxides of iron, cobalt, nickel,
magnesium, with other material.
• It has negative temp coefficient.
• It is mainly used for temperature measurement .
• It is found in different shapes like disc type, rod type
,washer type.
• Disc type – 10mm diameter
• It is mainly used for temperature control.
• Thermistors can be connected in series or parallel
combination
• It is also used in regulator circuits , memory units.

48. Differential output transducer
• It consists of a coil which is divided into to
parts.
• In response to displacement the inductance of
one part increases form L to delta and other
part from L-deltaL

49. • The output represents a change of self
inductance due to change of response.

50. LVDT
• The transformer consists of single primary
winding P1 and two secondary windings s1
and S2 wound on hollow cylindrical former.
• The primary is connected to ac source.
• The displacement to be measured is applied
to arm attached to the soft iron core.
• When the core is its normal position equal
voltages are induced in the two secondary
windings.

51. • If the core is moved to the left of the null
position more flux links with windings s1 AND
LESS WITH WINDINGS S2.
• Hence output voltage es1 of the secondary
winding s1 is greater than es2.
• If the core is moved to right position the flux
linking with winding s2 becomes greater than
the linked winding S1.

54. • The Rotational Variable Differential Transformer
(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. A schematic
is shown below.

56. • 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.
• The core must be in contact (directly or indirectly) with
the measured surface which is not always possible or
desirable.
•