How to avoid a ground loop – It’s not only a problem with accelerometers

When using modern, high technology measurement devices one can often be tripped up by the simplest things. The most common is the ground loop. Time and again this issue rears…

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What Type of Accelerometer Should I Use? IEPE, Charge or Bridge-based?

What type of accelerometer should I use? What are the advantages/disadvantages of a charge mode accelerometer, an IEPE accelerometer and a bridge based accelerometer?

There are so many types of accelerometer that is often difficult to know what type of accelerometer to use. An IEPE accelerometer will have a high pass filter at about 5Hz. The charge type will, by it’s nature have what is effectively a high pass filter at about 0.1Hz. Therefore neither type will show DC levels. The charge type will usually have a lower frequency bandwidth than the IEPE type. Charge accelerometers can be used at higher temperatures however. (more…)

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What Is A Hammer Test Or Hammer Impact Test?

This is often also known as Modal Testing. It is a method of testing that allows us to calculate the natural frequencies (modes), modal masses, modal damping ratios and mode shapes…

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How do I balance a shaft?

“How do I balance a shaft?” seems like a fairly straightforward question, but there are a number of things that we need to understand first. Here we look at a number of key concepts that need to be understood in order perform balancing.

What does balance mean?

Well broadly speaking to balance a shaft, mass must be added or removed at certain angles. The concept being that the centre of gravity and rotational centre of the shaft will be equal when the shaft is balanced. (more…)

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New Hammer Impact Software – Preview coming soon

After listening to customer feedback, we have completely re-engineered the DATS Hammer Impact software. The new version will ship with the next DATS update (not the soon-to-be-released V7.0.23). In the meantime you will be able to download and preview the new package. You will of course need a P8000 system and a DATS licence with the Hammer Impact option enabled. (more…)

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How Do I Get An XYZ Resultant Waterfall

A user has three signals captured using a triaxial accelerometer and asked “What is the simplest way to get the XYZ resultant from run-up file?” He had tried forming a resultant of the raw time histories, but didn’t fully understand the resultant time history.

Of course, the correct way of processing the data is to calculate the individual waterfalls from the x, y & z data and then calculate a resultant waterfall. (more…)

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What is Source Contribution Analysis (or SCA)?

How do you measure the causes of a noise or vibration with respect to several sources? Which source is causing what part of the response?

For example, how does the noise inside the cabin of a vehicle relate to the engine noise or wheel hub noise and vibration? (more…)

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Vibration : Measure Acceleration, Velocity or Displacement?

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 require the measured signals in a different form. Clearly, it is impractical to measure all three at once even if we could. Physically it is nigh on impossible to put three different types of transducer in the same place.

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Using Your VCM To Monitor Auxiliary Equipment

The use of a vibration condition monitoring system for monitoring vibration from large rotating machines fitted with fluid-filled journal bearings such as steam or gas turbines is well understood. Vibration from these components generally falls within the main harmonics or orders of the shaft rotational speed such as 1st, 2nd 3rd or 4th harmonic. Some energy may also exist below the 1st order, called the sub-synchronous component. Most energy exists below 1KHz and so standard displacement probes or velocity transducers are generally fitted. The Prosig PROTOR system collects this data in amplitude and phase form, relative to a ‘once-per-revolution’ phase reference signal, as standard and allows data to be displayed in real-time as mimic diagrams, trend plots, orbit and vector displays.

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Do You Need To Measure Brake Noise?


The objective of the brake noise tests was to record the braking events of cars being driven on various types of road and classify those events according to their type (Groan, Creep or Squeal etc) and severity. To do this the customer needed a system capable of working for long periods inside a vehicle in fairly tough conditions (high ambient temperatures, rough road) that was both quick to install and to remove.

On previous tests a system from another supplier had turned out to be unreliable and had failed to cope with the harsh environment. The analysis processing had also proved tedious and time consuming due to the huge amount of data created when testing several vehicles over many days.

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Read more about the article A Simple Frequency Response Function
Figure 5: H1(f)

A Simple Frequency Response Function

The following article will attempt to explain the basic theory of the frequency response function (FRF). 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 FRF is a mathematical representation of the relationship between the input and the output of a system.

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Acceleration, Velocity & Displacement Spectra – Omega Arithmetic

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.

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Measuring For Success With A Hammer Impact Test

The following application note shows the steps taken to perform structural analysis using a hammer impact test on an automotive exhaust pipe structure to improve the structural damping properties of the exhaust pipe mount. This application note follows up to a previous article – “Preventing Component Failure In The Fast Lane”.

A recent signal processing application note described how the Prosig sponsored Dalmeny Racing Formula Ford Team, whilst contesting the UK Formula Ford 1600cc championship, suffered several minor structural failures on a particular part of an exhaust pipe mount. Prosig dispatched a team of engineers, and after a brief survey of the damage, the engineers made an outline assessment. They concluded that “the exhaust itself is resonating at particular engine speeds. This is causing some shear forces in the mount. This in turn is causing stresses in the material leading to cracking and eventually failure.”

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A Simple Automotive Noise Test

In a recent article we described how the Prosig P8000 hardware and DATS software had been used to help Dalmeny Racing diagnose a problem with an exhaust bracket on their Formula Ford racing car. Whilst the car was instrumented for structural tests on the exhaust the opportunity was taken to carry out a simple automotive noise test. It was felt that these would provide some useful “real world” data as well as maybe providing some extra information regarding the exhaust bracket failure. After analysing and animating the hammer data it became clear that the engine runup data wouldn’t be needed. However, it was decided that some analysis should be carried out to see if the noise and vibration data backed up the conclusions of the other tests.

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Non Linear Calibration Curve And Polynomial

Not all systems vary linearly. One very well known case is, of course, thermocouples. International standard curves are available for these so they present little difficulty. The issue discussed here is determining a non linear calibration curve and if appropriate reducing to a polynomial.

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