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You will need a Crankshaft inductive pulse pick-up like this one (they are usually used for stroboscopes or for rpm measurements by clipping around the spark plugs. We have a few of this model, Please contact us if you would like one.
And make the following small assembly which is a tension divider bridge:
the Jack is ready to be connected directly into a recorder (MiniDisc, MP3, tape recorder...) or in the Line entry if your sound card on your laptop. The clip must be attached to a spark plug. All vehicles do not have the same gain at exit of the clip, you can replace the resistance of 100K Ohms by a potentiometre, which will enable you to adapt the amplitude of the signal as well as possible.
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The technique is simple, this assembly will make it possible to record the impulses with to the spark plug in a Wav file. The analysis of the Wav file, will allow to see the time passed between each spark, to deduce the engine speed from it, as well as the acceleration of the engine according to the rpm. We can then extrapolate the acceleration of the vehicle via information of gear/ratios of the gear box and the tyre size.
Here are the details of a correct recording
Record of a trial
You have three possibiltés to carry out the recording of a trial. Either you have a laptop and you will be able to use the real time option. Or you have a tape recorder, DAT or MiniDisc.
first case: not real time
Before carrying out the recording you will have to aquire a recording software and a sound editing package. You will be able to use, for example, Goldwave , which is a shareware. You will be able to find without too many problems, an equivalent in Freeware, by carrying out a research on Google for example.
Carry out all of the connections, using the AutoDiag kit or a clip on a wire of sparkplug. Connect the jack on the audio input of your tape recorder, MiniDisc, DAT.
drive a few kilometers to heat up your engine as well as well as your tyres (the coefficient of friction decreases with the temperature of the tyres). The measuring accuracy depends on the conditions under which will carry it out to you. The ideal is to use a very flat road, on a day without rain and wind. If you think that the road is slightly sloping, you will have the possibility of carrying out a test in each direction and of merge the two results. The ideal is also to make measurement on the same road, and starting in the same place.
The recording is carried out in general by using the 2nd gear/ratio of box. Indeed, even if you go to the limit, there is little chance so that you exceed legal speed (do not make these tests downtown of course) and the duration of the recording will remain lower than 15s.
Drive very slowly (1500 rpm), and begin the recording of the signal and 1 second after that press down on the accelerator to the limit (flywheel open to 100%) until the wished rpm level, pass the next gear and stop the recording. I advise you to not be alone while doing this test.
Launch GoldWave (or other), made connection between the headphone output of your tape recorder, MiniDisc or DAT and the entry line in the sound card of your PC.
the acquisition of the signal is done in 44100 Hz, 8 bits, Mono. With GoldWave, start by creating a file as follows :
Regulate the level of acquisition on the Line entry In via the mixing table. The signal must not be chopped, to prevent this make sure the horizontal bars of the noise level do not come into obstinate:
Press on the play key of your tape recorder, MiniDisc, DAT and on the record key of Goldwave to recover the signal on your microphone.
Record your Wav file. It is now necessary to carry out cleaning of the signal, by removing the part which is before you accelerate flat out(beginning of recording) and the part when you cahnge the gear until the end of the recording. Also check that the amplitude of the signal is correct, the largest peaks, should not be located below 0.5.
Click here for a preview
Record your Wav file. It is ready to be recovered by PowerDyn. If you have a laptop, you could also have directly recorded the signal by the intermediaire of GoldWave. It is an alternative to the real time method (explained further), which allows you, during the first tests, to ensure that the signal is correct (noise, form, amplitude...).
Launch PowerDyn and then configure a vehicle, séléctionnez le en double cliquant dessus dans la liste, puis choisissez l'option fichier wav ou txt dans la boite déroulante avant de cliquer sur l'icone Couple et Puissance.
Load your wav file by clicking on the yellow folder, choose the gear/ratio on which you carried out the measurement, regulate the threshold of detection according to your signal. If you wish to bring back your measurement of power in the CNTP (normal conditions of temperature and pressure), select to use correction SAE This will allow you to compare two measurements carried out under different conditions weather. Then click on the green Play button to obtain your result. Carry out the smoothing of the graph if you wish to, but do not exceed level 4 drawing aside too much from reality. Finally click on the diskette to associate your measurement to the selected vehicle.
Click here for a preview
The result can seem erroneous or not display, there are several possible reasons :
- PowerDyn could not isolate all the valid impulses because the signal is too strong. It interprets parasites like impulses. Either it will not be able to interpret your signal, or the power obtained will be too significant. To try to correct the probleme, you can open your Wav file (with GoldWave for example) and 'clean up' the 4 first impulses, by reducing to silence the parasites between the valid impulses. PowerDyn, posseses a mechanism of synchronization on the first impulses :
This signal was cleaned by removal of the parasitic peaks between the 4 first real impulses.
- PowerDyn could not isolate all the valid impulses because the signal is too weak. It misses the impulses and the power obtained is too low. It is necessary to remake the measurement and increasing the gain. If despite everything you do not obtain a correct signal, you can try to reduce the effect of the tension divider bridge. It can also be a question of a spark plug, a HT cable, or a defective reel.
- The restitution is very chaotic: PowerDyn does not manage to isolate all the valid impulses and counts some in more or less (according to the level of noise). check the level of recording, and carry out a new measurement. .
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