Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin vibrationem ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, such as the movement of a tire on a gravel road. here in this Presentation we can understand various vibration measurement instruments and their principals.

1. Name: JAIMIN AJITKUMAR KEMKAR
En. No.: 160123119014
Sem./Class/Batch: 6D1
Subject: DYNAMICS OF MACHINERY (2161901)
Guided By: Prof. PARANJAY PATEL

2. CONTENT
 INTRODUCTION TO VIBRATION
 BASIC CONSTRUCTION OF VIBRATION MEASURING
INSTRUMENTS
 CLASSIFICATION OF INSTRUMENTS
 VIBROMETERS

3. INTRODUCTION TO VIBRATION
 VIBRATION:
 When any elastic body such a spring, shaft or Beam is displaced from the
equilibrium position by the application of external forces and then released
it commences cyclic motion. such cycle of motion of a body or a system,
due to elastic deformation under the action of external forces is known as
vibration.
 Vibration measuring instruments are used to know vibration due to
earthquake, fluctuating wind velocities on structure or buildings random
vibrations due to Ocean waves, etc.

4. BASIC CONSTRUCTION OF VIBRATION
MEASURING INSTRUMENTS
 The vibration measurement process start by sensing the vibratory motion
from vibrating machine of structure and converting it into an electrical signal
with the help of transducer or pickup
 Output signal from transducer which is in the form of voltage or current is
too small to record it
 Therefore the signal conversion unit is used to amplify the signal from the
transducer to the required value
Vibrating
machine or
structure
Vibration
transducer or
pickup
Signal
conversion
unit
Display unit Data analysis

5.  The output signals from the signal conversion unit is displayed on display
unit for visual inspection. This information is recorded and stored into
computer for later use
 Finally, the data can be analyzed to know the vibration characteristics of
machine or structure

6. CLASSIFICATION OF INSTRUMENTS
 The vibratory response of A vibrating system can be expressed in terms
of various parameters such as:
1. Displacement (Amplitude)
2. Velocity
3. Acceleration
4. Frequency
5. induced stresses
 the choice of parameter depends upon the objective and field of
application

7. Vibration measuring
instruments
Based on contact between
vibrating system and
instrument
Contact type
Non contact type
Based on requirement of
power source
Active instruments
Passive instruments
Based on method of
measurement
Indicating type
instruments
Recording type
instruments

8. VIBROMETERS
 Vibrometers or seismometer is an instrument which measures the
displacement of a vibrating machine or structure
 The various type of amplitude measuring instruments are as follows
1. Stylus recording instrument
2. Seismic instrument or seismometer or vibration pickup
3. Optical recording instrument
4. Capacitance pickup
5. Simple Potentiometer
6. Mutual inductance pickup

9. 1.STYLUS RECORDING INSTRUMENTS
 It consists of a drum which is
rotating about Y-Y axis and a
stylus which is pivoted at a
fulcrum ‘O’. To the other end of the
stylish a link is attached which
pickups the vibratory motion from
vibrating machine or structure.
 The motion between the rotating
drum and linear moment of stylus
plot an amplitude of vibratory
motion on paper which is attached
on drum

10. 2. SEISMIC INSTRUMENT
 A seismic instrument consists of a spring-
mass-damper system in a frame or casing
which is mounted on the vibrating machine
or structure to measure the displacement
amplitude of a vibratory motion
 The Mask 'm' is supported in a frame or
casing by means of spring having 'K' and
dashpot of damping coefficient 'c'. the
frame or kissing his fastened to the vibrating
body so that it vibrates along with the
vibrating body. Thermometer is equivalent
to a spring-mass-damper system having a
base or support excitation

11. 3. OPTICAL RECORDING INSTRUMENT
 Light source sends the light signal through a lens to on mirror. The mirror is
attached to a vibrating body by means of some linkage.
 The light which is reflected from the mirror falls on a sensitized film on the
revolving drum and lots the displacement of vibratory motion

12. 4. SIMPLE POTENTIOMETER
 It consists of a voltmeter a
battery and resistance.
 A needle is connected to the
vibrating body and it is
allowed to slide on the
resistance
 The change in voltage due to
movement of needle on the
resistance is recorded this
voltage is proportional to
the amplitude of vibrations

13. 5. CAPACITANCE PICK-UP
 Capacitance pickup is non-
contacting active type
vibration measuring
instrument
which generates an output
proportional to the
displacement of the
vibratory motion
 Change in capacitance due
to variation in the air gap
is utilized in an RC circuit
to indicate the amount of
the vibratory displacement

14. 6. MUTUAL INDUCTANCE PICK-UP
 The mutual inductance pick up is also
a non contacting active pickup which is very
useful for a non magnetic metallic vibratory
surface
 The mutual inductance Lm changes due to
the variation in the air gap between the
vibrating surface and the pick-up. This
changes the field due to Eddy current in the
vibrating body. this field opposes the field
set up by the primary coil. Output voltage
is modulated by the vibratory motion and
demodulated output is proportional to the
displacement

15. references
 Book:
 Dynamics of machinery (by Dr. F. B. Sayyad)
 Mechanical vibrations (by V. P. Singh)