﻿ Frequently Asked Questions for Vibration

# Oscillation

Oscillations are the vibration with time of a quantity such as force, stress, pressure, amplitude, velocity, acceleration or jerk.

## Vibration

The term vibration is defined as Mechanical oscillation or motion about a reference point of equilibrium.

### Periodic Vibration

A Vibration whose instantaneous value of any future time can be predicted by an exact mathematical expression. Sinusoidal Vibration is the classic example of periodic or Deterministic Vibration.

#### Forced Vibration

The Vibratory motion of a system caused by some mechanical excitation is known as forced Vibration.

##### Free- Vibration

Free- Vibration occurs without forcing

###### Acceleration

Acceleration is a rate of change of velocity with time. Usually along a specified axis & Denoted by 'g'

###### How Are Dust Samples Collected And Analyzed?

The simplest method of collecting dust is a surface wipe sample in an area of one square foot is sampled. To assure collection of all dust particles, the area is wiped several times in different directions. After collection, the dust sample is contained and sealed, then sent to a laboratory for assessment.

###### ‘g’

The acceleration produce by Earth’s gravity. By international agreement, the value of gravitational unit is 9.80665 m/ sec2

###### Amplitude

The magnitude of variation from its zero values known as Amplitude i.e. 0 to peak value.

###### Displacement

Displacement specified change of position and measured peak to peak. It is 2x amplitude of any variation.

###### Velocity

Rate of Change of displacement (x) with time, usually denoted by dx/ dt.

###### Frequency

The reciprocal of Time period (in seconds). It is measured in Hz.

###### Frequency Response

It is defined as the portion of frequency spectrum, which a device can cover within specified limit of error.

###### Fundamental Frequency

It is defined as the no. of cycles per second of the lowest frequency component of a complex, cycle motion.

###### Frequency Spectrum

A description of the resolution into frequency of any signal.

###### Natural Frequency

It is denoted by Fn and known as the frequency of an undamped system’s free vibration.

###### Resonance Frequency

Resonance frequency is the same as natural frequency. It is also called as critical frequency.

###### Distortion

The acceleration produce by Earth’s gravity. By international agreement, the value of gravitational unit is 9.80665 m/ sec2

###### RMS or root mean square value

The square root of the time-averaged squares of a series of measurements. In case of sine wave, the RMS value is 0.707 x Peak value

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###### Sine Vibration Rating

Sine vibration test is very common test having different profiles. Endurance by sweeping is the most appropriate method for simulating the effect of stress undergone by specimen in use. The displacement is associated with a corresponding value of acceleration in such a manner that the magnitude of vibration should be same at the cross over frequency. The frequency range may be thus programmed and swept continuously changing from constant displacement to constant acceleration and vice-versa at the cross-over frequency.

###### Random Vibration Rating

Acceleration (g) in random testing is defined in terms of r.m.s. Value and calculated on the basis of Power Spectral Density (PSD). Random ratings have been calculated as per the directions of International Standards Organization document ISO 5344. The force rating are based on flat spectrum 100 to 200 Hz with 20 db/ decades roll-off from 100 Hz down to 20Hz, with loads equal to or greater than twice the armature mass. ISO 5344 indicates that the ratio of peak to rms acceleration level must be at least 3:1 sigma, as measured on the vibration table.

###### Shock Vibration Rating

The shock capability of the system is determined by the test profile such as pulse duration, pulse amplitude, pre and post pulse structure etc. Dynamic Associates & Services should be consulted to provide the most suitable system.