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By Chris Mason on January 19th, 2010  Prosig have welcomed 2010 with the official launch of their PROLOG data acquisition controller.
PROLOG is a controller that will allow remote, unattended or standalone operation of a P8000 system. In normal operation a P8000 data acquisition system is connected to a laptop or PC and data is stored, in real-time, on the computers hard drive via the USB 2.0 interface. This configuration provides a robust, high speed data capture environment. However, there are situations where it is not practical to keep the laptop connected. In some cases the environment may be suitable for the P8000 unit, but not for some of the more fragile components in a laptop. In other situations it may be desirable to have the measurement system in one location, whilst the operator may be positioned some distance away. The PROLOG unit is designed to address both of these requirements.
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By James Wren on January 19th, 2010  I’m often asked what is the difference between free field microphones, diffuse field microphones and pressure microphones.
For a run-of-the-mill ½ inch microphone the short answer is nothing.
However the long answer is a bit more involved.
Basically if the sample rate is 10 kHz or below and an accuracy of ±2dB is acceptable then there is no real difference between the types.
So what is the difference between these types of microphone?
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By James Wren on October 19th, 2009 The 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 points on a structure using an accelerometer to measure the response and a force gauge hammer to measure the excitation.
Fundamentally a frequency response function is a mathematical representation of the relationship between the input and the output of a system.
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By John Mathey on September 1st, 2009 In this article we will look at why we need to consider energy correction when producing frequency spectra and how we go about it. We will use a perfect, ’special case’ signal to keep the explanation as simple as possible. The signal we will use is periodic within the time record used to calculate the FFT. Specifically, we will look at 1 second of 10Hz sinusoid with an amplitude of 1Vrms as seen in Figure 1.
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By John Mathey on July 20th, 2009 Before 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 be preserved during transformation. That is, the energy measured on time signal must equal the energy measured on the frequency representation of that signal.
- Second, an FFT converts the signal representation between time and frequency domains. The time domain representation shows when something happens and the frequency domain representation shows how often something happens.
- And finally, an FFT assumes that the signal is repetitive and continuous.
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By Dr Colin Mercer on June 22nd, 2009 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 will examine it using a filter based interpolation and a classical curve fitting procedure to obtain a better representation.
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By Chris Mason on April 22nd, 2009 
Following a discussion in the office about Fourier Transforms we did a little searching on the web. As always, we discovered that the Internet is packed with some great resources on Fourier and his work. So rather than keep all of the information to ourselves we thought we should share it with our readers. We have whittled our list down to 10 links that we think represent the whole range of information from beginners guides to reference pages. So there should be something for everyone whether you’re a grizzled signal processing veteran or a student looking to learn something new. If you have your own favourite Fourier links then please add them to the comments. Maybe we could use them for a future blog post. Or if you have other comments please feel free to add them below.
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By Adrian Lincoln on October 17th, 2008  Torsional 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 crankshaft rotary vibration. This vibration is transmitted to and modified further by other components in the powertrain such as the gearbox and by other equipment driven off the drive belt or chain. Additional torsional vibrations are also likely to appear downstream at the drive shafts and wheels.
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By James Wren on September 8th, 2008  A strain gauge is an electrical sensor which is used to accurately measure strain in a test piece. Strain gauges are usually based on a metallic foil pattern. The gauge is attached to the test piece with a special adhesive. As the test piece is deformed, so the adhesive deforms equally and thus the strain gauge deforms at the same rate and amount as the test piece. It’s for this reason that the adhesive must be carefully chosen. If the adhesive cracks or becomes detached from the test piece any test results will be useless.
Strain gauges are used not just for metals; they have been connected to the retina of the human eye, insects, plastics, concrete and indeed any material where strain is under investigation. Modern composite materials like carbon fibre when under development are often constructed with strain gauges between the layers of the material.
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By Don Davies on September 5th, 2008  Prosig have been awarded the contract to upgrade the Online Vibration Monitoring System at Wylfa nuclear power station.
Wylfa is located on the north coast of Anglesey and has two Magnox design nuclear reactors and four turbine generators. The station supplies 23 million kilowatt hours of electricity, enough to meet the needs of two cities the size of Liverpool and Manchester put together.
A PROTOR system has been installed and running Wylfa since 1998. The system monitors the four main steam turbine generators and also eight gas circulators, four for each of the two reactors. The system provides important vibration trends for these critical items of plant for both local and remote analysis.
The new contract is to replace the existing PROTOR-3 Remote Monitoring Data Analysis Systems (RMDAS) with new PROTOR-4 P4700 units. A total of eight P4700 units will be supplied, one for each main turbine and one to monitor a pair of Gas Circulators. The flexibility of the P4700 in handling multiple machines with individual tachometer or phase reference signals is ideally suited to this requirement.
By Don Davies on June 4th, 2008  Shaft displacement is an important vibration measurement for rotating machines. Shaft displacement is usually monitored by non-contact shaft displacement probes such as eddy-current probes. These probes produce a voltage proportional to the distance of the shaft surface relative to the tip of the probe. For maximum benefit, ideally two shaft displacement probes will be fitted to measure the displacement in both the horizontal and vertical directions. Actually the probes do not have to be exactly horizontal and vertical as PROTOR (http://www.prosig.com/protor) is able to resolve into the horizontal and vertical directions.
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By James Wren on April 14th, 2008  Most engineers are probably familiar with or have come across the decibel or dB as a unit of measurement. Its most common use is in the field of acoustics where it is used to quantify sound levels. However, as will be explained in this article, it is also useful for a wide variety of measurements in other fields such as electronics and communications.
One particular use of dB is to quantify the dynamic range and accuracy of an analogue to digital conversion system. This applies to Prosig’s P8000 range of data acquisition hardware where the noise floor, dynamic range and resolution are all specified in terms of dB.
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By James Wren on March 25th, 2008  The size and shape of the Prosig P8000 data acquisition systems greatly facilitates installation in locations that are small or difficult to access. Now Prosig can offer a new level of flexibility. Not only can the P8000 be used in the laboratory and in the automobile, but with the new mobile Prosig Power units they are truly portable. Now with the new Prosig Power units the systems can operate totally independently. The Prosig Power units can be mounted externally or internally and can provide several hours use. As well as improvements to portability the Prosig Power units can be used in situations where power supply from a vehicle is unstable such as during engine cranking.
The P8000 systems are light and easy to carry. They also offer flexible cable connections. The P8000 has a robust design and is capable of operating under extreme temperatures and harsh conditions. The low power consumption and low heat generation of the P8000 gives its advanced cooling system the flexibility to completely shut off the system fans during data captures thus providing absolute silence for acoustic measurements.
By Dr Colin Mercer on March 4th, 2008  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 phase for vibration monitoring. Most vibrations on a rotating machine are related to the rotational speed so it is clearly important to have a measure of the speed, either directly or as a once per revolution tacho pulse. A question some time arises as to whether a once per revolution tacho reference signal is needed to measure phase. Is it possible to get phase if we only have a speed signal? This note gives some insight into those questions. Actually the question that should be asked is – “Can we measure a meaningful phase, for use in vibration monitoring, if we only have a speed signal as well as the vibration signals?”
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By Dr Colin Mercer on November 30th, 2007 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 and occasional impulsive type vibration caused by, say, blasting and the like.
DIN 45669-1 describes the signal processing actions and DIN 4150-2 details how these are used. Provisions are included for day or night levels and for five categories of building:
- Industrial
- Predominantly Commercial
- Mixed Commercial and Residential
- Residential
- Special Areas such as Hospitals
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By Dr Colin Mercer on October 23rd, 2007 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 time (Orders from Hopping FFT) rather than as a function of speed (Waterfall). This is very useful when analyzing a complete operational cycle which includes run ups, rundowns and periods at operational speeds.
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By Adrian Lincoln on October 5th, 2007  It is quite straightforward to apply “classical” integration techniques to calculate either a velocity time history from an acceleration time history or the corresponding displacement time history from a velocity time history.
The standard method is to calculate the area under the curve of the appropriate trace. If the curve follows a known deterministic function then a numerically exact solution can be found; if it follows a non-deterministic function then an approximate solution can be found by using numerical integration techniques such as rectangular or trapezoidal integration. Measured or digitized data falls in to the latter category. However, if the data contains even a small amount of low frequency or DC offset components then these can often lead to misleading (although numerically correct) results. The problem is not caused by loss of information inherent in the digitisation process; neither is it due to the effects of amplitude or time quantisation; it is in fact a characteristic of integrated trigonometric functions that their amplitudes increase with decreasing frequency.
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By Dr Colin Mercer on September 12th, 2007  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 suitable for evaluating dissimilar vehicles and different types of pump.
Noise is an important consideration when a consumer is selecting a new vehicle. It is therefore imperative that every aspect of the vehicle’s acoustic profile is thoroughly understood and refined.
From an end user point of view the assessment criterion is simply how much will the driver or passengers hear the pump noise in relation to the vehicle background noise. That is, will the pump produce, what may be called, audible tones with the vehicle in different operating conditions.
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By Chris Mason on June 24th, 2007 Using Prosig’s P8000 series data acquisition system with DATS signal analysis software, torsional analysis (crank jitter) was performed on an automotive engine attached to an engine dynamometer. The significance of this is that only one tachometer channel was required to identify crank jitter.
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By James Wren on May 23rd, 2007  First, in order to explain resonance we have to explain the terms we will use.
• A resonance is a particular frequency.
• A period is the amount of time it takes to complete one cycle
• The number of cycles in one second is the frequency of an oscillation.
• Frequency is measured in Hertz, named after the 19th-century German physicist Heinrich Rudolf Hertz
• A single Hertz is equal to one cycle per second.
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By Chris Mason on April 7th, 2007  Prosig USA Inc. is proud to announce an alliance with SenSound, maker of powerful 3D acoustic holography software. To kick off the new Prosig / SenSound alliance a demo day has been scheduled to give engineers a thorough understanding of the potential available in acoustic testing. The demo will be at TechTown, in Detroit, MI, USA on April 11th 2007. Attendance is limited. Don’t be disappointed. Contact Prosig USA to book your place. If you can’t make the demo day, but would like further information of the Prosig/Sensound system or any of Prosig’s other products please contact sales@prosig.com.
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By James Wren on March 29th, 2007 Prosig were recently involved in the validation of a closed loop control system for an automotive pump supplier. The customer has a large number of test cells, each test cell has 8 pumps continually on test. Each pump is instrumented with a revolution or tachometer sensor, giving a once per revolution tachometer pulse. Additionally, there are various analogue transducers on each pump which measure parameters, such as pressure at the pump inlet and outlet.
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By Dr Colin Mercer on February 25th, 2007 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 squares of each of the FFT values. Mathematically, if Xks is the modulus (magnitude) of the kth value of the FFT at speed s for k = 1…N-1 then the rms value at that speed is given by
This takes into account the entire energy at that speed both the order and the non order components, including any noise.
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By Dr Colin Mercer on December 7th, 2006 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 potentiometer or LVDT transducers to measure absolute displacement directly as static reference points are available. But on a moving vehicle this is not possible.
More here… OmegaArithmetic.pdf
By Dr Colin Mercer on November 9th, 2006  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 meaningful manner so that they may be automatically recognised and either removed or extracted for analysis in a structured way.
There are two principle objectives initially: one is to be able to recognise an event and the other is to be able to mark it in some way so that subsequent software is able to operate on the actual event. We must also note that an event has a start and an end; the criterion we use to recognise the start may not necessarily be the same criterion we use to recognise the end. Searches for the start and end points are carried out on a Reference Signal. How the reference signal is formed is discussed in detail later, it includes the original signal, various running statistical measures such as the dynamic RMS, differentiation for slope detection, integration and so on. In many cases the start criterion will be some check on the level achieved by the reference signal. By the time any check level has been detected then it is almost certain that the event started earlier! That is, a pre trigger capability is essential.
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