working at the heart of test & measurement
working at the heart of test & measurement
Here you will find a wide selection of articles, notes and tutorials on many aspects of data acquisition, digital signal processing and real-world data measurement and analysis. These articles are free to download and read.
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. 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 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.
MEASURING TORSIONAL CRANK SHAFT JITTERUsing 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.
EVALUATING A CLOSED LOOP CONTROL SYSTEM FOR HIGH PRESSURE PUMPSProsig 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 are various analogue transducers on each pump which measure parameters, such as pressure at the pump inlet and outlet...
MEASURING FOR SUCCESSA 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.
FATIGUE AND DURABILITY TESTINGThis application note describes the test and measurement process for the fatigue testing and development cycle of a component. Strain gauges were used to monitor the strain levels in a particular suspension component. The component had been known to fail at various intervals. A predicted life for the component was required to analyse the feasibility of the its continued use or to see if a design change was required.
EXHAUST DEVELOPMENT USING A PROSIG P8000 SYSTEMThe 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 exhaust manufacturer in Europe. The particular vehicle under test was required by local legislation to have an overall radiated noise level of less than 70 dB. When tested, the vehicle was found to be producing 71.8 dB of radiated noise. The design of the exhaust system clearly needed to be reviewed and modified.
ANALYZING SHAFT TWIST AND REPARING DAMAGED TACHOSA 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.
A SIMPLE NOISE TESTIn a recent article we described how the Prosig P5000 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 also take some noise and vibration readings during an engine run up.
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 = 1...N-1 then the rms value at that speed is given by...
TORSIONAL VIBRATION, TACHO PULSES & ALIASINGWith 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 pulse at regular angular intervals. It we have N pulses per rev then obviously we have a pulse every (360/N) degrees. Determining the speed is nominally very simple: just measure the time between successive pulses. If this period is Tk seconds and the angle travelled is (360/ N) degrees then the rotational speed is simply estimated by 360/(N*Tk) degrees/second or 60/(N*Tk) rpm...
AVERAGE WATERFALLS OR ORDERS?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 is not the case. Why is there a difference? The answer is what is sometimes called the picket fence effect and, at other times, is called "scalloping loss".
TORSIONAL VIBRATIONMeasuring twist in shafts and geartrains.
FREQUENCY, HERTZ & ORDERSAn examination of the relationship between frequency and orders.
HIGH PASS FILTERING AND TACHO SIGNALSThe perils and pitfalls of filtering your tacho signal.
For any online condition monitoring system such as PROTOR the setup of alert limits for vibration data is of major importance and often requires extensive experience of the characteristics of the machine and is usually time-consuming. Selection of limits such that significant events are triggered and where spurious indications are kept to a minimum is the desired aim and requires careful consideration. Failure to achieve this results in any system being seen as unreliable and therefore rarely used to its full potential.
TIME TO TESTThe PROSIG P5600 / DATS Data Acquisition and Analysis system helps save time and money at Ford Motor Company, Dearborn, MI.
In this note the different types of transducers that can be used with the Prosig P8000 series data acquisition system are discussed. The article deals with the design and function of the different types of transducer and the applications they are normally associated with.
NOTES ON FOURIER ANALYSISFourier 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. The resultant summed signal is shown in the third graph.
WHAT IS RESONANCE ?In technical terms resonance is the tendency of a structure or material to oscillate at maximum amplitude at a certain frequency. This frequency is known as the structures "resonant frequency"
ACCELERATION, VELOCITY & DISPLACEMENT SPECTRA – OMEGA ARITHMETICAccelerometers 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.
DYNAMIC RANGE & OVERALL LEVEL : WHAT ARE THEY?Accurate measurement of a signal depends on both the dynamic range and the overall level.
DATA DECIMATIONThe do's, dont's and why's of downsampling, upsampling, anti-aliasing and the Nyquist Frequency.
TIME VARYING OVERALL LEVELWhat are the differences and relationships between overall level, RMS, SD & dynamic SD?
INTERPRETATION OF THE ARTICULATION INDEXWhat is AI and how is it used?
"STANDARD" OCTAVE BANDSWhere do octave band center frequencies come from?
A, B & C WEIGHTINGWhy we need to weight and unweight data. And how we do it.
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 ups, rundowns and periods at operational speeds.
EXAMPLES OF EVENT EXTRACTION AND REMOVALIn many cases only significant events, such as bumps or other transients, in a signal are of relevance. The objective is to be able to isolate these events in a meaningful manner so that they may be automatically recognised and either removed or extracted for analysis in a structured way.
PHASE BETWEEN SIGNALSThe objective is to demonstrate calculation of the time varying phase between a reference signal (tacho) and a sine wave. Two test signals were generated. The first signal was an eight second bandlimited tacho signal at 20Hz (1200 RPM). The other signal was a phase modulated sinewave.
AUDIO EQUALISATION FILTER & PARAMETRIC FILTERINGWhen working with audio signals a common requirement is to be able to equalise, cut or boost various frequency bands.
CLEANING UP DATAUsing a median filter to remove spikes from data.
SMOOTHING SPECTRAL DATASometimes data has spikes that are clearly artefacts of the processing.
DOES YOUR SIGNAL HAVE A GAUSSIAN RANDOM DISTRIBUTION?Find out how a Disney film can help in classifying your data.
DATA SMOOTHING: RC FILTERING & EXPONENTIAL AVERAGINGWhat are RC Filtering and Exponential Averaging and how do they differ?
DIFFERENTIATING & INTEGRATING SIGNALS NUMERICALLYWhy differentiation and integration may cause surprises when carried out numerically.
NON-LINEAR CALIBRATION CURVE & POLYNOMIALCalibrating a nonlinear measurement system using DATS.
CORRELATION EXAMPLEHow DATS for Windows can help in analyzing correlation.
DON'T LET SPIKES SPOIL YOUR DATAWhy it's not wise to ignore the "odd" spike in your data.
REMOVING LAG USING PHASELESS FILTERINGA phaseless filtering technique that eliminates time lag.
GETTING RID OF SPIKESHow DATS can be used to get rid of those annoying spikes.
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| P8000 Series |
 Up to 256 channels Up to 400k samples / second / channel 24-bit analog input USB 2.0 102dB dynamic range -120dB noise floor CAN/GPS Thermocouple & strain gage conditioning Analog output High speed tacho processing Full signal conditioning Comprehensive application software |
| DATS.toolbox |
 Data Acquisition (Capture) 2D & 3D Graphs Data Arithmetic Frequency Spectra Time Domain Analysis Digital Filtering Curve Fitting Shock Spectra Data Generation & Synthesis Probability Analysis Maths, Statistics & Calculus Data Import & Export Built-in Report Generator Worksheet Automation Script (Macro) Automation. Click to find out more |
| RealWave Analyser |
 The Realwave Pocket Analyser is a handheld, PDA-based analyser that addresses many applications including realtime FFT analysis, spectrograms, octave analysis, vibration level meter with human vibration filter, sound level meter & FFT based RPM meter. And prices start from just £1385. Click to find out more |
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| DATS.nvh |
 Waterfalls Order Tracking Sound Quality Metrics Tacho Analysis Waterfall Averaging A, B, C, D Weighting Frequency Spectra 1/nth Octave Bands Worksheet Automation Script (Macro) Automation Click to find out more |
| Free 2007 Catalog |
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| DATS.rotate |
 Waterfalls Order Tracking Tacho Analysis Waterfall Averaging Time Domain Analysis Frequency Domain Analysis Order Domain Analysis Shaft Twist Torsional Vibration Worksheet Automation Script (Macro) Automation Click to find out more |