Dr Colin Mercer : Noise & Vibration Blog : What You Need To Know About Noise & Vibration Measurement

About Author: Dr Colin Mercer

Website: http://www.linkedin.com/pub/colin-mercer/21/102/535
Description: Dr Colin Mercer is the Technical Director of Prosig and has prime responsibility for signal processing and its applications. He was formerly at the Institute of Sound and Vibration research (ISVR), Southampton University where he founded the Data Analysis Centre. He is a Chartered Engineer and a Fellow of the British Computer Society.

Posts by Dr Colin Mercer

Where Does The Noise Come From?
Posted on May 14, 2012 | 2 Comments
When one thinks of noise in a signal it is generally associated with having been added in some way to the amplitude of a signal. This is not always the...
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Why is the microphone pressure reference 2*10^-5 Pascals?
Posted on February 7, 2012 | No Comments
This seemingly simple question is actually quite fundamental. To answer the question we need to consider sound intensity. Now sound intensity is defined as “the average rate of flow of...
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Negative Frequencies – What Are They?
Posted on December 13, 2011 | 2 Comments
Normally when we are analysing a signal it is a purely real signal, that is it has no imaginary part. A classic example is of course a sine wave. When...
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Vibration : Measure Acceleration, Velocity or Displacement?
Posted on September 5, 2011 | 3 Comments
When using vibration data, especially in conjunction with modelling systems, the measured data is often needed as an acceleration, as a velocity and as a displacement. Sometimes different analysis groups...
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Do Missing Tacho Pulses Mean The End Of The Road For Your Test?
Posted on September 20, 2010 | No Comments
Creating a stable, good quality tacho signal can be one of the hardest parts of analyzing rotating machinery. So what happens if our carefully designed and implemented tacho misses a...
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Removing A-Weighting From Time History Signals
Posted on July 22, 2010 | No Comments
It sometimes occurs that signals are captured with A-weighting applied to the data by the acquisition device. This can be a problem if, for example, you wish to use the...
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Aliasing, Orders and Wagon Wheels
Posted on June 29, 2010 | No Comments
These days most people collecting engineering and scientific data digitally have heard of and know of the implications of the sample rate and the highest observable frequency in order to...
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Interpolation Versus Resampling To Increase The Sample Rate
Posted on June 22, 2009 | 4 Comments
These are two different techniques aimed at different objectives. First consider a simple sinewave that has been sampled close to the Nyquist frequency (sample rate/2). Visually this looks very pointy. We...
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Vibration Monitoring Phase Measurement And The Tacho Signal
Posted on March 4, 2008 | 5 Comments
Any vibration signal may be analyzed into amplitude and phase as a function of frequency. The phase represents fifty percent of the information so it is most important to measure...
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Human Exposure To Vibration In Buildings (DIN 4150-2:1999-06 & DIN 45669-1:1995-06)
Posted on November 30, 2007 | 4 Comments
Standards DIN 4150-2:1999-06 and DIN 45669-1:1995-06 provide a means of assessing the effect on human beings of vibration caused by vehicle traffic, trains both above and below ground, construction work...
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Orders v Time – Comparing Overall Levels
Posted on October 23, 2007 | 4 Comments
By combining a speed signal with a data signal and using the Short Time FFT algorithm (Hopping FFT), it is possible to extract order data directly as a function of...
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Sound Steering
Posted on September 12, 2007 | No Comments
The requirement was to develop a ‘standard’ test for assessing the sound quality of power steering pumps in vehicles. Measurements needed to be objective so that the method would be...
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Order Cuts And Overall Level
Posted on February 25, 2007 | No Comments
Order cuts are taken from a set of FFTs, each one at a different rpm. The rms level is then found as the Square root of the Sum of the...
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Acceleration, Velocity & Displacement Spectra – Omega Arithmetic
Posted on December 7, 2006 | 18 Comments
Accelerometers are robust, simple to use and readily available transducers. Measuring velocity and displacement directly is not simple. In a laboratory test rig we could use one of the modern...
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Examples Of Event Extraction And Removal
Posted on November 9, 2006 | 1 Comment
In many cases only significant events, such as bumps or other transients in a signal are of relevance. The objective is to be able to isolate these events in a...
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Standard Octave Bands
Posted on February 17, 2006 | 6 Comments
The “standard” centre frequencies for 1/3 octave bands are based upon the Preferred Numbers. These date from the 19th century when Col. Charles Renard (1849–1905) was given the job of...
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Torsional Vibration, Tacho Pulses And Aliasing
Posted on January 12, 2006 | 4 Comments
With shafts, gears and the like, the general method of determining the rotational speed is to use some form of tachometer or shaft encoder. These give out a pulse at...
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Analyzing Shaft Twist And Repairing Damaged Tachos
Posted on October 19, 2005 | 1 Comment
A shaft has been instrumented with two shaft encoders, one at each end. Each shaft encoder gives out a once/rev pulse and a 720 pulses/rev signal. Each signal was digitised...
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Phase Between Signals
Posted on August 9, 2005 | 4 Comments
The following article was written in response to a question from a visitor to the website. The gentleman in question had been reading some of the Prosig signal processing articles...
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Average Waterfalls Or Average Orders?
Posted on June 14, 2005 | No Comments
One would expect that averaging waterfalls and then extracting orders would give the same result as extracting orders from individual waterfalls and then averaging them. This is not the case.
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Audio Equalisation Filter & Parametric Filtering
Posted on May 17, 2005 | No Comments
When working with audio signals a common requirement is to be able to equalise, cut or boost various frequency bands. A large number of hardware devices on the market provide...
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Cleaning Up Data
Posted on September 22, 2003 | No Comments
When we have a very noisy signal with a large number of spikes and signal bursts then if all else fails try Median Filtering. This is a technique often used...
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Notes On Fourier Analysis
Posted on July 29, 2003 | 14 Comments
Fourier analysis takes a signal and represents it either as a series of cosines (real part) and sines (imaginary part) or as a cosine with phase (modulus and phase form)....
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Data Smoothing : RC Filtering And Exponential Averaging
Posted on April 28, 2003 | 7 Comments
What are RC Filtering and Exponential Averaging and how do they differ? The answer to the second part of the question is that they are the same process! If one...
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Smoothing Spectral Data
Posted on July 15, 2002 | No Comments
Sometimes data has spikes which are clearly artefacts of the processing or are due to some other external source. One is used to seeing these on time series but in...
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