This document discusses different types of transducers used to measure vibration, including variable resistance, piezoelectric, and electrodynamic transducers. It also describes accelerometers, which specifically measure acceleration. Variable resistance transducers detect changes in electrical resistance from mechanical motion. Piezoelectric transducers generate electrical charges when subjected to mechanical stresses or forces. Electrodynamic transducers produce voltages through the interaction of a moving coil within a magnetic field. Accelerometers are widely used to measure vibration and earthquakes, with different types including shear, flexural, and compression mode accelerometers.

1. Table of Contents
1- Introduction.............................................................................................................1
2- Transducers.............................................................................................................1
3- Variable Resistance Transducer..............................................................................2
4- Piezoelectric Transducer.........................................................................................3
5- Electrodynamic Transducers...................................................................................3
6- Accelerometer.........................................................................................................4
6-1 Type of Accelerometers......................................................................................4
7- References...............................................................................................................5
List of Figure
Fig- 2 Basic vibration measurement scheme .................................................................1
Fig- 3 Electric resistance strain gage. ............................................................................2
Fig- 4 Strain gage as vibration pickup. ..........................................................................2
Fig- 5 Piezoelectric Transducer .....................................................................................3
Fig- 6 Electrodynamic Transducers...............................................................................4
Fig- 7 Accelerometers....................................................................................................5

2. 1 | P a g e
1- Introduction
the motion (or dynamic force) of the vibrating body is converted into an electrical
signal by the vibration transducer or pickup. In general, a transducer is a device that
transforms changes in mechanical quantities (such as displacement, velocity,
acceleration, or force) into changes in electrical quantities (such as voltage or
current). Since the output signal (voltage or current) of a transducer is too small to
be recorded directly, a signal conversion instrument is used to amplify the signal to
the required value. The output from the signal conversion instrument can be presented
on a display unit for visual inspection, or recorded by a recording unit, or stored in a
computer for later use. The data can then be analyzed to determine the desired
vibration characteristics of the machine or structure. Depending on the quantity
measured, a vibration measuring instrument is called a vibrometer, a velocity meter,
an accelerometer, a phase meter, or a frequency meter. If the instrument is designed to
record the measured quantity, then the suffix meter is to be replaced by graph.
Fig- 1 Basic vibration measurement scheme
2- Transducers
A transducer is a device that transforms values of physical variables into equivalent
electrical signals. Several types of transducers are available; some of them are less
useful than others due to their nonlinearity or slow response. Some of the transducers
commonly used
The type of vibration measuring Transducers depend on:
- The expected range of frequencies and amplitudes
- The size of machine / structure involved
- Conditions of operation of the machine / structure
- Type of data processing used

3. 2 | P a g e
3- Variable Resistance Transducer
In these transducers, a mechanical motion produces a change in electrical resistance
(of a rheostat, a strain gage, or a semiconductor), which in turn causes a change in the
output voltage or current.
An electrical resistance strain gage consists of a fine wire whose resistance changes
when it is subjected to mechanical deformation. And the resulting change in its
resistance is given by
Fig- 2 Electric resistance strain gage.
Fig- 3 Strain gage as vibration pickup.

4. 3 | P a g e
4- Piezoelectric Transducer
Certain natural and manufactured materials like quartz, tourmaline, lithium sulfate,
and Rochelle salt generate electrical charge when subjected to a deformation or
mechanical stress, The charge generated in the crystal due to a force is given by
Qx = kFx = kApx
E = vtpx
5- Electrodynamic Transducers
When an electrical conductor, in the form of a coil, moves in a magnetic field a
voltage E is generated in the conductor. The value of E in volts is given by
E = Dlv
Fig- 4 Piezoelectric Transducer

5. 4 | P a g e
Fig- 5 Electrodynamic Transducers
6- Accelerometer
accelerometer is an instrument that measures the acceleration of a vibrating body
Accelerometers are widely used for vibration measurements and also to record
earthquakes. From the accelerometer record, the velocity and displacements are
obtained by integration.
6-1 Type of Accelerometers
• Shear Mode Accelerometer
• Flexural Mode Accelerometer
• Compression Mode Accelerometer

6. 5 | P a g e
Fig- 6 Accelerometers
7- References
[1] Theory of Vibration with Applications 4th
Edition by “William Thomson” is
Emeritus Professor at the University of California
[2] Mechanical Vibrations 5th
Edition by “SINGIRESU S. RAO”