Instrumentalities For Vibrational Patterns Determination:Oscillometric Orientation💠VibrationalTheory
0Vibration Measurement
Vibration can be considered to be the oscillation or repetitive motion of an object around an equilibrium position. Vibrations usually occur because of the dynamic effects of manufacturing tolerances, clearances, rolling and rubbing contact between machine parts and out-of-balance forces in rotating and reciprocating members.
Table of contents
Where do vibrations come from?
What are vibrations?
Machine vibration
Vibration level
Vibration parameters
What is acceleration and what is an accelerometer
Basic principle of an accelerometer
Types of accelerometers
Piezoelectric acceleration sensors
Static acceleration sensors - MEMS sensors
Choosing the correct sensor
Choosing the mounting position for the accelerometer
Eddy-current sensor
Measurement instrument selection
Channel setup for vibration measurement
Acceleration sensor setup
Velocity and displacement calculation
Vibration analysis - acceleration, velocity and displacement
Vibration measurement - example
Bearing fault analysis - Envelope detection
Where do vibrations come from?
Vibration can be considered to be the oscillation or repetitive motion of an object around an equilibrium position. The equilibrium position is the position the object will attain when the force acting on it is zero.
Vibrations usually occur because of the dynamic effects of manufacturing tolerances, clearances, rolling and rubbing contact between machine parts, and out-of-balance forces in rotating and reciprocating members. Often, small insignificant vibrations can excite the resonant frequencies of some other structural parts and be amplified into major vibration and noise sources.
Image 1: Vibrations caused by an unbalanced wheel
Sometimes mechanical vibration is needed. For example, we generate vibration intentionally in component feeders, concrete compactors, ultrasonic cleaning baths, rock drills, and pile drivers. Vibration testing machines are used extensively to impart a controlled level of vibration energy to products and sub-assemblies where it is required to examine their physical or functional response and ascertain their resistibility to vibration environments.
Image 2: Vibrations caused by a drilling machine
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What are vibrations?
The vibrating body describes an oscillating motion about a reference position. The number of times a complete motion cycle takes place during the period of one second is called the frequency and is measured in hertz (Hz).
The motion can consist of a single component occurring at a single frequency, as with a tuning fork, or of several components occurring at different frequencies simultaneously, as for example, with the piston motion of an internal combustion engine.
On the image below we can see the motion of a tuning fork. A tuning fork is an acoustic resonator in the form of a two-pronged fork. It resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object and emits a pure musical tone.
Image 3: Vibrating tuning forks
The signal from tuning the fork in the Dewesoft recorder and on the FFT widget.
Image 4: Signal from tuning fork in time and in the frequency domain
In the image below we can see the motion of the piston, which can be found in internal combustion engines.
Image 5: Motion of a piston in internal combustion engines
The signal from piston motion in Dewesoft recorder and on FFT widget.
Image 6: Vibration from piston motion in time and in the frequency domain
Vibration signals in practice usually consist of many frequencies occurring simultaneously so that we cannot immediately see just by looking at the amplitude-time pattern, how many components there are, and at what frequencies they occur.
These components can be revealed by plotting vibration amplitude against frequency. The breaking down of vibration signals into individual frequency components is called frequency analysis, a technique which may be considered the cornerstone of diagnostic vibration measurements.
The graph showing the vibration level as a function of frequency is called a frequency spectrogram. When frequency analyzing machine vibrations we normally find a number of prominent periodic frequency components that are directly related to the fundamental movements of various parts of the machine. With frequency analysis, we are, therefore, able to track down the source of undesirable vibration.
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Machine vibration
Most of us are familiar with vibration; a vibrating object moves - oscillates.
There are various ways we can tell that something is vibrating. We can touch a vibrating object and feel the vibration. We may also see the Emovement of a vibrating object. Sometimes the vibration creates sounds that we can hear o hea
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