Force transducers use elastic members where applied forces cause displacement or strain that is sensed mechanically or electrically. Common types are axially loaded elastic members and cantilever-type elastic members. Measurement methods include mechanical dial gauges, linear variable differential transformers (LVDTs), piezoelectric transducers, and resistance strain gauges. LVDTs and strain gauges are widely used as they can measure small displacements or strains electrically with high sensitivity and repeatability. Piezoelectric transducers generate electric charges when subjected to mechanical stress.

1. Presented by-
Bhupendra kumar singh

2.  These are important device for the measurement
of both static and dynamic forces.
 The force applied to the elastic member result in
a displacement or strain in the elastic member,
which is sensed by mechanical or electro-
mechanical mean.

3.  Axially loaded elastic member;-
 E= Young modulus
 K= stiffness

4.  Cantilever-type elastic member;-

5.  1- Mechanical method
 2-Electromechanical methods
 (i) LVDT
 (ii) Piezo-electric transducer
 (iii) Resistance strain gauge

6.  A mechanical method involving the use of a
dial gauge .
 The elastic ring, called the
proving ring.

7.  Linear variable-differential transformer(LVDT)
 The linear variable-differential transformer(LVDT)
is the most widely used inductive transducer to
translate linear motion into electrical signal

8.  Any physical displacement of the core causes
the voltage of one secondary winding to
increase while simultaneously, reducing the
voltage in the other secondary winding.
 The difference of the two voltages appears
across the output terminals of the
transducers and gives a measure of the
physical position of the core and hence the
displacement.

9.  The transducers possess a high sensitivity.
 The transducers have low hysteresis and
hence repeatability is excellent under all
conditions.
 They have infinite resolution.
 They are simple,light in weight and easy to
maintain.

10.  They are sensitive to stray magnetic fields but
shielding is possible.
 They are inherently low in power output.
 Temperature affects the performance of
transducer.

11.  The LVDT can be used in all applications
where displacements ranging from fraction of
a mm to a few cm have to be measured.
 Acting as a secondary transducer it can be
used as a device to measure force, weight
and pressure.

12.  Appearance of an electric
potential across certain
faces of a crystal when it
is subjected to
mechanical pressure
 Conversely, when an
electric field is applied to
one of the faces of the
crystal it undergoes
mechanical distortion.

13.  The material that show significant and
useful piezoelectric effect fall under three
main groups:
1. Natural, Eg: Quartz, Rochelle salt
2. Synthetic, Eg: Lithium Sulphate, Ammonium
Dihydrogen Phosphate
3. Polarized Ferroelectric Crystals, Eg: Barium
Titanate, Lead Zirconate-Titanate

15.  There are two families of
 constants which are used
 to describe the piezoelectric
 effect:
• g constant
• d constant
 These are written as gij and dij
 Where,
 i= direction of electric effect
 j= direction of mechanical
effect

16.  Applied Piezo: Applications
 Piezoelectric materials are used in
numerous applications.
 The direct piezoelectric effect is used in e.g.
 generators (e.g. gas igniters)
 sensors (e.g. accelerometers, pressure
sensors)
 switches (e.g. in control panels)
 ultrasonic transducers (e.g. in medical
imaging)

17.  A strain gauge is an example of passive
transducer that converts a mechanical
displacement into a change of resistance.
 A strain gauge is a thin, wafer-like device
that can be attached to a variety of
materials to measure applied strain.

18.  The majority of strain gauges are foil types,
available in a wide choice of shapes and sizes
to suit a variety of applications. They consist of
a pattern of resistive foil which is mounted on a
backing material.
 They operate on the principle that as the foil is
subjected to stress, the resistance of the foil
changes in a defined way.

19.  The strain gauge is connected into a
Wheatstone Bridge circuit. The change in
resistance is proportional to applied strain
and is measured with Wheatstone bridge.

20.  The sensitivity of a strain gauge is described in
terms of a characteristic called the gauge
factor, defined as unit change in resistance per
unit change in length, or
 Gauge factor is related to Poisson's ratio µ by,
K=1+2 µ

21. Based on principle of working :
• Mechanical
• Electrical
• Piezoelectric
Based on mounting :
• Bonded strain gauge
• Unbonded strain gauge
Based on construction :
• Foil strain gauge
• Semiconductor strain gauge
• Photoelectric Strain gauge

22. Advantages
 There is no moving part.
 It is small and inexpensive.
Disadvantages
 It is non-linear.
 It needs to be calibrated.

23.  Residual stress
 Vibration measurement
 Torque measurement
 Bending and deflection measurement
 Compression and tension measurement
 Strain measurement

24. THANK YOU