W : Sound and Vibration Terms, Definitions, Units, Measurements ..
W : under Watt
Warble Tone : sound whose frequency varies periodically about a mean value.
Waterfall : a 3-D plot displaying the amplitude of spectral components as a function of both time and frequency. The frequency spectrum is displayed as a curve for each specified time instant. Several such curves, for different time instants, are displayed simultaneously.
Waveform : the waveform is the shape of a time domain signal as seen on an oscilloscope screen. It is a visual representation or graph of the instantaneous value of the signal plotted against time. Inspection of the waveform can sometimes reveal information about the signal that the spectrum of the signal does not show.
For instance a sharp spike or impulse and a randomly varying continuous signal can have spectra that look almost identical, while their waveforms are completely different.
In machine vibration, spikes are usually caused by mechanical impacting, while random noise can be caused by the advanced stages of bearing degradation
W = m g : where W = weight, m = mass and g = acceleration (m/s2).
So Weight and Mass are related, but not the same thing. An object with a mass of 1 kg would weigh about 9.8 Newtons on Earth, but 6 times less on the moon, due to Gravity. In space an object still has mass but is weightless.
In everyday use the term weight nearly always means mass. In science weight is the
Force due to Gravity and the units are Newtons.
Weighting Networks : an electronic filter in a sound level meter or a vibration meter that correlates the objective meter measurement to the human response.
For example the frequency response of the human ear, in which case the
A-weighting Network is most commonly used with regard to noise control issues, regulations and environmental standards.
Similarly Hand arm and
Whole Body measurements are frequency dependent. There are a range of human vibration networks or filters because measurements are made in 3-axis and the weightings for whole body measurements, seated, standing or lying down are different from the hand arm filters see the list below.
Weighting Network : Bb : for measuring whole body vibration in fixed-guide transport systems in seated or recumbent positions.
Weighting Network : Bc : for measuring horizontal whole body vibration in the X direction, perpendicular to the spinal column, at the seat back.
Weighting Network : Bd : for measuring horizontal whole body vibration in the X and Y directions, at right angles to the spinal column, in seated, standing or recumbent positions.
Weighting Network : Be : for measuring rotational whole body vibration in 3-axis.
Weighting Network : Bg : for evaluation of whole body vibration in the Z direction, with regard to hand control and visibility.
Weighting Network : Bh : for measuring hand arm vibration in the X / Y / Z axis.
Weighting Network : Bj : for measuring vibration acting on the head of a recumbent person in the vertical direction, perpendicular to the lying surface.
Weighting Network : Bk : for measuring whole body vibrations in the direction of the spinal column in seated and standing positions, for measurements in the vertical direction, perpendicular to the lying surface in recumbent position and for measurements in the X / Y / Z axis acting on the feet in seated position.
Weighting Network : Bm : for measuring whole body vibrations in buildings in the X / Y / Z axis.
Weighting Window :
Fast Fourier Transform theory tells us that time and frequency are simply two alternative ways of observing a signal. By changing the nature of a signal in the
Time Domain, we implicitly change the nature of the spectrum in the frequency domain. This is exactly what we do when we apply a weighting function or
White Finger : disorder of the hands caused by using hand-held tools, such as chain saws and jack hammers. Results in reduction of the hand's ability to feel or to regulate its temperature. May also result in numbness and excessive sensitivity to low temperatures. Called Raynaud's disease.
White Noise : noise whose Power Spectral Density is essentially independent of frequency, so is characterless. However levels measurements using sound analysers with 1/1 or 1/3 octave (Constant Percentage Bandwidth) filters will increase by 3dB for each increasing frequency step. Pink noise on the other hand will produce constant levels across the spectrum.
Whole-body Vibration is defined as mechanical vibration which is transmitted into the body, when seated or standing, through the supporting surface, during a work activity.
Our bodies are exposed to vibration at work from many machines, such as construction machinery (bulldozers, tow motors, fork lifts and cranes), heavy equipment (grinders, jack hammers), and power hand tools. Vibration has been proven to result in disorders of both the hand and arm, the neck, and the back.
Windowing : a technique used to reduce
Spectral Leakage by multiplying the
Time Domain waveform by a window function. The process of windowing reduces the amplitudes of discontinuities at the edges of a waveform, thereby reducing the Spectral Leakage.
Windscreens : the 'foam' windscreens extensively used with sound level meters present some interesting problems. They reduce the wind noise by perhaps 15 dB or more on a good day, so in windy conditions how do you know you are measuring the noise source or the wind or a combination of the two? **
Some guidance is given in ISO 1996 (community noise survey noise standard) which recommends you measure downwind at wind speeds of between 1 and 5 m/s. This can result in wind 'generated' noise levels of around 30dB (A) with the windscreen on.
** a practical solution is to listen to the AC output of the sound level meter using earphones, or the audio recording feature included in some sound level meters like the B&K 2250