Prosig Noise & Vibration Measurement Blog » orders

Aliasing, Orders and Wagon Wheels

Dr Colin Mercer — Tue, 29 Jun 2010 09:51:21 +0000

These days most people collecting engineering and scientific data digitally have heard of and know of the implications of the sample rate and the highest observable frequency in order to avoid aliasing. For those people who are perhaps unfamiliar with the phenomenon of aliasing then an Appendix is included below which illustrates the phenomenon.

In saying that [...]

Measurement And Analysis Of Torsional Vibration

Adrian Lincoln — Fri, 17 Oct 2008 07:44:13 +0000

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 [...]

Vibration Monitoring Phase Measurement And The Tacho Signal

Dr Colin Mercer — Tue, 04 Mar 2008 09:52:09 +0000

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 [...]

Orders v Time – Comparing Overall Levels

Dr Colin Mercer — Tue, 23 Oct 2007 13:33:06 +0000

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 [...]

Sound Steering

Dr Colin Mercer — Wed, 12 Sep 2007 09:54:20 +0000

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 [...]

Measuring Torsional Crank Shaft Jitter

Chris Mason — Sun, 24 Jun 2007 07:43:54 +0000

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.

Figure 1: A Prosig P8020

The Prosig P8020 data acquisition unit (see figure [...]

Order Cuts And Overall Level

Dr Colin Mercer — Sun, 25 Feb 2007 14:38:43 +0000

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 [...]

Exhaust Development Using A Prosig P8000 System

James Wren — Mon, 20 Feb 2006 11:17:48 +0000

The following note describes an application of the Prosig P8000/DATS system in the refinement of an automotive exhaust muffler design for a major after-market [...]

Torsional Vibration, Tacho Pulses And Aliasing

Dr Colin Mercer — Thu, 12 Jan 2006 15:44:34 +0000

With shafts, gears and the like, the general method of determining the rotational speed is to use some form of tachometer or shaft encoder. These give out a [...]

Analyzing Shaft Twist And Repairing Damaged Tachos

Dr Colin Mercer — Wed, 19 Oct 2005 09:22:40 +0000

A shaft has been instrumented with two shaft encoders, one at each end. Each shaft encoder gives out a once/rev pulse and a 720 pulses/rev signal. Each signal was digitised at 500,000 samples/second. The objective is to measure the twist in the shaft and analyze into orders. The test stand was already equipped with a data [...]

A Simple Noise Test

James Wren — Fri, 26 Aug 2005 19:53:35 +0000

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 [...]

Average Waterfalls Or Average Orders?

Dr Colin Mercer — Tue, 14 Jun 2005 20:51:52 +0000

One would expect that averaging waterfalls and then extracting orders would give the same result as extracting orders from individual waterfalls and then averaging them. This [...]

Audio Equalisation Filter & Parametric Filtering

Dr Colin Mercer — Tue, 17 May 2005 14:14:20 +0000

When working with audio signals a common requirement is to be able to equalise, cut or boost various frequency bands. [...]

Torsional Vibration Example

Dr Colin Mercer — Wed, 15 May 2002 10:10:09 +0000

The measurement of the twist angle between two points along a shaft or through a gear train may be derived from a pair of tacho signals, one at each end of the shaft. Typically the tacho signals would be derived from gear teeth giving a known number [...]

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 [...]