signal processing Archive
Why is the microphone pressure reference 2*10-5 Pascals?
Posted on January 31, 2012 | No CommentsThis 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...
Measuring Torsional Vibration 101
Posted on January 24, 2012 | No CommentsDo you need to measure torsional vibration? Interested in shaft twist? Worried about rotational jitter? Don’t worry, we’ve got it covered. Here we have gathered together our most popular articles...
How To Calculate A Resultant Vector
Posted on January 12, 2012 | No CommentsWe can distinguish between quantities which have magnitude only and those which have magnitude and are also associated with a direction in space. The former are called scalars, for example,...
Negative Frequencies – What Are They?
Posted on December 13, 2011 | 1 CommentNormally 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...
What is Synchronous (Angular) Sampling?
Posted on November 9, 2011 | No CommentsThe term synchronous data is usually applied to vibration or acoustic data that is captured from an item of rotating equipment at regularly spaced angle intervals as distinct from regularly...
Understanding Filter Characteristics
Posted on October 4, 2011 | 2 CommentsRecently when discussing with an engineering student the characteristics of filters, it became clear that some confusion exists around this subject area. This note attempts to explain the differences between types...
Video: Noise & Vibration From Rotating Machines
Posted on October 4, 2011 | No CommentsThis is complete version of the video illustrating my recent article How To Measure Noise & Vibration In Rotating Machines. This video was previously published on the blog in 3 parts....
Vibration : Measure Acceleration, Velocity or Displacement?
Posted on September 5, 2011 | 3 CommentsWhen 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...
Understanding Windowing And Overlapping Analysis
Posted on August 30, 2011 | 2 CommentsThe following article was inspired by a question asked by a reader regarding my previous article - Data Windows : What, why and when?. Specifically, the reader asked “Could you please...
How To Analyze Noise & Vibration In Rotating Machines
Posted on August 9, 2011 | 3 CommentsIn this article we will look at the basic steps behind a simple rotating machinery study. We won’t look in great detail at some of the techniques involved – we deal with...
Which Should I Use? Real & imaginary? Or magnitude & phase?
Posted on May 4, 2011 | 7 CommentsIn one of our recent articles a question was asked regarding the practical use of real & imaginary type plots compared with modulus & phase type plots. In general, noise...
What Is The Difference Between Single Ended & Differential Inputs?
Posted on February 15, 2011 | No CommentsProsig P8000 systems use differential inputs, but what are they and why are they so special? This subject is not always fully understood and, therefore, the focus of this article...
Converting Acceleration, Velocity & Displacement
Posted on December 16, 2010 | 9 CommentsFrom time to time I meet engineers who are interested in the conversions between acceleration, velocity and displacement. Often, they have measured acceleration, but are interested in displacement or vice...
High Dynamic Range – Fact or Fiction?
Posted on November 18, 2010 | 3 CommentsAt least one manufacturer of data acquisition systems claims to achieve an incredibly high dynamic range (160dB) when capturing data. This is supposedly achieved by the use of dual-range data...
Do Missing Tacho Pulses Mean The End Of The Road For Your Test?
Posted on September 20, 2010 | No CommentsCreating 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...
Developing an Algorithm for Tick Detection
Posted on August 23, 2010 | 3 CommentsAn investigation was made of a sample of automotive components where some were exhibiting a high frequency “tick” or rattle during each operating cycle. This feature could be heard above...
Removing A-Weighting From Time History Signals
Posted on July 22, 2010 | No CommentsIt 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...
Aliasing, Orders and Wagon Wheels
Posted on June 29, 2010 | No CommentsThese 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...
The Intelligent Way To Sort, Extract & Analyze Signals
Posted on May 10, 2010 | 1 CommentThis note is based on a real requirement presented to Prosig by a prospective user. It’s the sort of challenge that we relish. This case is a great example of...
The Causes of Road Noise
Posted on March 30, 2010 | 1 CommentRoad noise (the noise produced by the interaction of tires and road surface) is in many circumstances the dominant noise experienced by vehicle occupants. The requirements for producing quieter roads...
A Simple Frequency Response Function
Posted on October 19, 2009 | 20 CommentsThe following article will attempt to explain the basic theory of the frequency response function. This basic theory will then be used to calculate the frequency response function between two...
Amplitude And Energy Correction – A Brief Summary
Posted on September 1, 2009 | 8 CommentsAmplitude and energy correction has been and is a continuing point of confusion for many people calculating spectra from time domain signals using Fourier transform methods. The first thing to...
Data Windows : What, why and when?
Posted on July 20, 2009 | 7 CommentsBefore we discuss the use of data windows, we should first remind ourselves of three basic properties of the FFT (Fast Fourier Transform) process. First, energy information in signal must...
Interpolation Versus Resampling To Increase The Sample Rate
Posted on June 22, 2009 | 5 CommentsThese 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...
Measurement And Analysis Of Torsional Vibration
Posted on October 17, 2008 | 13 CommentsTorsional vibration is of key importance in the area of vehicle development and refinement. The main contributory source is the engine where periodically occurring combustion cycles cause variation in the...
