A reference dictionary of sound and vibration terms
  • Data Acquisition System
    Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems (abbreviated with the acronym DAS or DAQ) typically convert analog waveforms into digital values for processing. The components of data acquisition systems include:
    a. Sensors that convert physical parameters to electrical signals.
    b. Signal conditioning circuitry to convert sensor signals into a form that can be converted to digital values.
    c. Analog-to-digital converters, which convert conditioned sensor signals to digital values.

    Data acquisition applications are controlled by software programs developed using various general purpose programming languages such as BASIC, C, FORTRAN, Java, Lisp, and Pascal. COMEDI is an open source API (application program Interface) used by applications to access and controls the data acquisition hardware. Using COMEDI allows the same programs to run on different operating systems, like Linux and Windows. Specialized software tools used for building large-scale data acquisition systems include EPICS. Graphical programming environments include ladder logic, Visual C++, Visual Basic, MATLAB and LabView.
  • Acceleration
    In physics, acceleration is the rate of change of velocity over time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity.

    In classical mechanics, for a body with constant mass, the acceleration of the body is proportional to the net force acting on it (Newton's second law):

    Where F is the resultant force acting on the body, m is the mass of the body, and a is its acceleration.
  • Transducer/Sensor
    A transducer is a device that converts one type of energy to another. The conversion can be to/from electrical, electro-mechanical, electromagnetic, photonic, photovoltaic, or any other form of energy. While the term transducer commonly implies use as a sensor/detector, any device which converts energy can be considered a transducer.
  • Resonance
    In physics, resonance is the tendency of a system to oscillate with larger amplitude at some frequencies than at others. These are known as the system's resonant frequencies. At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores vibrational energy. Resonances occur when a system is able to store and easily transfer energy between two or more different storage modes (such as kinetic energy and potential energy in the case of a pendulum). However, there are some losses from cycle to cycle, called damping. When damping is small, the resonant frequency is approximately equal to a natural frequency of the system, which is a frequency of unforced vibrations. Some systems have multiple, distinct, resonant frequencies.
  • Time domain
    Time domain is a term used to describe the analysis of mathematical functions, or physical signals, with respect to time. In the time domain, the signal or function's value is known for all real numbers, for the case of continuous time, or at various separate instants in the case of discrete time. An oscilloscope is a tool commonly used to visualize real-world signals in the time domain. Speaking non-technically, a time domain graph shows how a signal changes over time, whereas a frequency domain graph shows how much of the signal lies within each given frequency band over a range of frequencies.
  • Amplitude
    Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation. If a variable undergoes regular oscillations, and a graph of the system is drawn with the oscillating variable as the vertical axis and time as the horizontal axis, the amplitude is visually represented by the vertical distance between the extrema of the curve.
  • Signal
    In the fields of communications, signal processing, and in electrical engineering more generally, a signal is any time-varying or spatial-varying quantity. In the physical world, any quantity measurable through time or over space can be taken as a signal. Within a complex society, any set of human information or machine data can also be taken as a signal. Such information or machine data (for example, the dots on a screen, the ink making up text on a paper page, or the words now flowing into the reader's mind) must all be part of systems existing in the physical world – either living or non-living.
    Analog and digital signals
    Less formally than the theoretical distinctions mentioned above, two main types of signals encountered in practice are analog and digital. In short, the difference between them is that digital signals are discrete and quantized, as defined below, while analog signals possess neither property.
  • Vibration (Oscillation)

    Vibration refers to mechanical oscillations about an equilibrium point. 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. Vibration is occasionally "desirable". For example the motion of a tuning fork, the reed in a woodwind instrument or harmonica, or the cone of a loudspeaker is desirable vibration, necessary for the correct functioning of the various devices.
    More often, vibration is undesirable, wasting energy and creating unwanted sound – noise. For example, the vibrational motions of engines, electric motors, or any mechanical device in operation are typically unwanted. Such vibrations can be caused by imbalances in the rotating parts, uneven friction, the meshing of gear teeth, etc. Careful designs usually minimize unwanted vibrations. The study of sound and vibration are closely related. Sounds, or “pressure waves”, are generated by vibrating structures (e.g. vocal cords); these pressure waves can also induce the vibration of structures (e.g. ear drum). Hence, when trying to reduce noise it is often a problem in trying to reduce vibration.
    Free vibration occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely. Examples of this type of vibration are pulling a child back on a swing and then letting go or hitting a tuning fork and letting it ring. The mechanical system will then vibrate at one or more of its "natural frequency" and damp down to zero. Forced vibration is when an alternating force or motion is applied to a mechanical system. Examples of this type of vibration include a shaking washing machine due to an imbalance, transportation vibration (caused by truck engine, springs, road, etc.), or the vibration of a building during an earthquake. In forced vibration the frequency of the vibration is the frequency of the force or motion applied, with order of magnitude being dependent on the actual mechanical system.

  • What is machine vibration?
    Most of us are familiar with vibration; a vibrating object moves to and fro, back and forth. A vibrating object oscillates. However, we experience many examples of vibration in our daily lives. A pendulum set in motion vibrates. A plucked guitar string vibrates. Vehicles driven on rough terrain vibrate, and geological activity can cause massive vibrations in the form of earthquakes.

    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 back-and-forth movement of a vibrating object. Sometimes vibration creates sounds that we can hear or heat that we can sense. To observe how vibration can create sound and heat, rub your feet back and forth on a carpet.

    01-mechanical vibration-machine vibration-examples-industrial machine vibrations-automobile vibration-guitar vibration

    In industrial plants there is the kind of vibration we are concerned about: machine vibration.
    What is machine vibration? Machine vibration is simply the back and forth movement of machines or machine components. Any component that moves back and forth or oscillates is vibrating.

    Machine vibration can take various forms. A machine component may vibrate over large or small distances, quickly or slowly, and with or without perceptible sound or heat. Machine vibration can often be intentionally designed and so have a functional purpose. (Not all kinds of machine vibration are undesirable. For example, vibratory feeders, conveyors, hoppers, sieves, surface finishers and compactors are often used in industry.)

    At other times machine vibration can be unintended and lead to machine damage. Most times machine vibration is unintended and undesirable. This article is about the monitoring of undesirable machine vibration.
    Shown below are some examples of undesirable machine vibration.
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    For getting the undesired vibration, we are often required to do the NVH test. The test equipment includes:
    Analyzers, shakers and controllers, accelerometers, noise dosimeters, octave band filters, transducers for vibration and acoustics, dynamometers, sound level meters, microphones, and analysis software.

    With technology changing every day, focus is shifting more toward the development of PC based analyzers, multichannel NVH data acquisition systems, acoustic holography devices, laser vibrometers, and anechoic test cells. The NVH test equipment manufacturers can be classified as product vendors and solution providers.

    Product vendors supply devices that fulfill certain end users, usually called application specialists, whereas solution providers design products that cater to the clients’ requirements. They often face the end users including aerospace & defense, automotive, industrial, consumer products, and building construction among others, often have a great need of the test equipment.

    The undesired vibration and noise are often solved by the NVH test equipment manufacturer.
  • Who can benefit from NVH test ?
    Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured, Harshness is a subjective quality, and is measured either via "jury" evaluations, or with analytical tools that provide results reflecting human subjective impressions. These latter tools belong to the field known as "psychoacoustics”. And our escalating demands for safety and physical well being mirror our increased awareness of the effects of noise and vibration
    In automatic industry, NVH test deal with both noise and vibration experienced by the occupants of the transportation vehicle and the noise radiated by vehicle, such as drive-by noise testing, the mechanical shocks imposed on them, brake testing etc. The cars are extensively tested to make sure they can withstand the mechanical shocks imposed on them. The noise that cars make will have been analyzed to make sure that it’s comfortable for the driver and passenger and it does not spoil the environment of those around you. There’s no doubt that the customers of automobile industry would benefit directly from the NVH test.
    Definitely, the automatic manufactures who appreciate such measures will benefit from such regulations. As they care about their customers’ requirement and pay more attention to the component design process, the manufactures would beat the competitors during the frenetic manufacturing competition.
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