A method to identify subjectively objectionable disturbances (e.g. piston slap, valve tick,… etc) in internal combustion engines

## Generating speed v time information from noise & vibration signals

Picture the scenario; you have captured some noise & vibration data from a rotating machine. Typically, this might be noise in a vehicle cabin, but could have been anything from a tiny pump to a full size power station turbine.…

## Understanding Phase Measurements

When performing frequency analysis of vibration data for any application the resultant spectrum has both amplitude and phase components, therefore the phase component represents half of the information available and can provide a valuable insight into the causes of the…

## How Do I Convert Between Acceleration, Velocity & Displacement?

One of the most searched for and read topics on the Noise & Vibration Measurement Blog is that of converting between measurements of acceleration, velocity and displacement. To help anyone looking for posts on this topic we’ve collected all of…

## What Is Resonance? (Part 3)

In the previous two articles (What Is Resonance? (Part 1) & What Is Resonance (Part 2)) in this series we have looked at how we can identify a resonant frequency. Now we will discuss what happens next. What do we…

## A Guide To Digital Filtering

Understanding filters is actually simpler than it may first seem. Creating a filter is another story; it’s like being able to drive a car without having to know the intricate details of how the engine and its electronics work. When…

## A Different Way Of Averaging – Time Synchronous Averaging

Assuming one wants a frequency spectrum from an acquired time measurement, it is generally accepted that averaging of a signal in the time domain is not very useful due to the randomness of the start of the time block used…

## Quantifying Signals – Peak, Peak-to-Peak, & RMS metrics

Anytime you measure something which is changing with time, there are multiple ways to quantify the signal. For the purpose of this discussion, we will be talking about how to describe the signal in the time domain. There are several ways to…

## What Can I Do About Spikes In My Data?

Whether you call them spikes, glitches, anomalies or data dropouts, these phenomena have been a problem to engineers ever since they started recording data. There are any number of reasons why these problems occur. Sometimes it may be possible to…

## What Are AC and DC Coupling?

This is an important subject to understand when working in the signal processing field. In terms of AC and DC Coupling, what is Coupling? Quite simply, coupling is the transfer of energy from one medium to another, for example, from…

## Understanding & Measuring Noise

There are many reasons to measure and analyze noise. It may relate to legislation or regulations that limit noise in certain environments, we could be using the noise to investigate a related issue or maybe simply improving the noise of…

## What is Resonance? (Part 2)

This article is a follow on from What Is Resonance? (Part 1) and answers some of the issues not covered in that post. How do you find the resonant frequency in the real world? What do you do when there…

## Waterfall Analysis: Frequency Spectrum or Order Spectrum?

This article addresses two basic approaches to analyzing rotating machinery during transient (sweeping rpm) conditions. The first is the traditional method which uses Frequency (FFT) Spectrum analysis at target rpm values throughout a run up or a coast down condition.…

## Wide Band Integrators – What Are They?

For some time now it has been conventional ‘wisdom’ that using time based digital integration may cause amplitude errors in the result and that these get worse as the frequency increases. As a result of this, integration using Omega arithmetic has been prevalent by using Fourier Transforms of the signal. This, of course, remains a valid approach and is particularly useful if the data is already in the frequency domain, which was its prime purpose.

## Noise & Vibration Analysis: Back To Basics

Sometimes it doesn’t hurt to revisit some of the basic building blocks that form the foundation of what we do. And so we have gathered together a few of our most popular past articles that deal with the fundamental aspects…

## Where Does The Noise Come From?

[latexpage] 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 case. The two sinewaves shown in Figure 1 appear…

## Waterfall Analysis: Frequency Resolution and Smearing

When measuring noise and vibration in rotating machines, especially complex devices like automobile engines, it is very important to fully understand what is being measured and what analyses need to be performed on the resulting data. Even the most sophisticated…

## Understanding the Importance of Transducer Orientation

When monitoring vibration on large gas or steam turbines and generators with fluid-film bearings, the relative movement of the shaft within the bearing is typically measured by a pair of shaft proximity (eddy current) transducers. Data from these transducers is…

## Testing Times : Why & How We Measure Noise & Vibration

We’re going to look today at some of the practical aspects of how we measure noise & vibration and consider why it’s important that you should measure and, more importantly, understand the noise and vibration of your products The current…

## Why is the microphone pressure reference 2*10^-5 Pascals?

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 energy through a unit area normal to the direction of…

## Measuring Torsional Vibration 101

Are you interested in measuring torsional vibration? Need to measure shaft twist? Worried about rotational jitter? Don’t worry, we’ve got it covered. Here we have gathered together our most popular articles on the subject of torsional vibration to give you…

## How To Calculate A Resultant Vector

When we are dealing with multiple measurements we often need to calculate a resultant vector to understand their combined effect. What do we mean by this? And how do we calculate the resultant vector? We can distinguish between quantities which…

## Negative Frequencies – What Are They?

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 we analyse a signal with a Fourier transform, typically using…

## What is Synchronous (Angular) Sampling?

The 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 spaced time intervals. The rotating part could be an engine,…