We 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, mass and temperature. The latter are called vectors, for example,…

## How To Analyze Noise & Vibration In Rotating Machines

In this article we will look at the basic steps needed to measure noise & vibration in rotating machines. We won’t look in great detail at some of the techniques involved – we deal with these elsewhere on the blog. This material…

## 9 Great Engineering Animations

Here is a great little collection of engineering animations from the simple everyday to the more sophisticated. A brilliant way to learn how things work. We hope you like them. Please leave your comments. 4-speed Gearbox Engine power enters through the shaft…

## Converting Acceleration, Velocity & Displacement

From 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 versa. Equally, velocity is often used to find acceleration. This article outlines the nature of the conversion between these units and will suggest the preferred method for doing so. .

## 10 Sites That Every Engineer Should Know About

Here’s another post inspired by an office discussion. We were discussing our favourite engineering based websites and realised the results would make a great blog post. So after a rummage through our bookmarks and a little further debate we’ve come…

## A Simple Frequency Response Function

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…

## What Are dB, Noise Floor & Dynamic Range?

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…

## Calculating Velocity Or Displacement From Acceleration Time Histories

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.

## What Is Resonance?

We hear the word used a lot, but what is resonance? First, in order to explain we have to explain the terms we will use. A period is the amount of time it takes to complete one cycle The number…

## Understanding The Cross Correlation Function

To illustrate the use of the cross correlation function, a source location example is shown below. For this, it is assumed that there is a noise source at some unknown position between 2 microphones. A cross correlation technique and a…