Prosig Noise & Vibration Measurement Blog » Nyquist

10 Educational Mechanical Engineering Videos

Chris Mason — Mon, 17 May 2010 13:44:11 +0000

We’ve had a good look around YouTube and dug up a great collection of educational mechanical engineering videos. There’s a wide range of information here from simple maths tutorial to explanations of the inner workings of the internal combustion engine. We hope you enjoy watching and if you have any favorites of your own please drop [...]

Interpolation Versus Resampling To Increase The Sample Rate

Dr Colin Mercer — Mon, 22 Jun 2009 14:12:21 +0000

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.

As a second example we will look at a [...]

Evaluating A Closed Loop Control System For High Pressure Pumps

James Wren — Thu, 29 Mar 2007 11:57:54 +0000

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 [...]

Notes On Fourier Analysis

Dr Colin Mercer — Tue, 29 Jul 2003 14:39:56 +0000

Fourier analysis takes a signal and represents it either as a series of cosines (real part) and sines (imaginary part) or as a cosine with phase (modulus and phase form). As an illustration we will look at Fourier analysing the sum of the two sine waves

shown below. [...]

Frequency, Hertz & Orders

Dr Colin Mercer — Sun, 03 Feb 2002 17:09:46 +0000

The most common form of digitising data is to use a regular time based method. That is data is sampled at a constant rate specified as a number of samples/second. The Nyquist frequency, fN, is defined such that fN = SampleRate/2. As discussed elsewhere Shannons Sampling [...]

Data Decimation. What Do I Do?

Dr Colin Mercer — Wed, 06 Jun 2001 14:13:40 +0000

Sometimes we have digitised data at a much higher rate than we need. How can we reduce the sampling rate? If I wanted to say halve the sample rate can I just throw away every other data point?

The answer is NO, except in pathological conditions where you know that there is no frequency content above [...]

Removing Phase Delay Using Phaseless Filtering

Dr Colin Mercer — Wed, 06 Jun 2001 09:16:07 +0000

In many instances we need to filter a signal to remove unwanted frequencies. If we use classical filters such as Butterworth, Chebyshev or even Bessel then a phase delay is introduced. This phase delay is itself a function of frequency so that the signal content at one frequency is delayed a different amount to that at [...]