Work in Progress
DEPAC Method of Dyno Instrumentation:
All other Dyno instrumentation packages use a simplistic method called 'A/D Sampling'. It is easy to understand but the method is not accurate. It is easily affected by 'noise' and has limited application. Its primarily used for high speed 'strip-chart' data recording, like you have from an on-board race car recorder. The mistake is trying to use this method for other applications, like dyno instrumentation. SAE Dyno standards state that 1% accuracy is all that's required. Yes, Sampling can squeak-in just under 1% so it does meet the (poor) standards.
The DEPAC instrumentation is based on sound methods (without compromise) yielding results 100's of times more precise and meaningfull compared to 'A/D sampling'. DEPAC Instrumentation exceeds the SAE Standards of accuracy by 100's of times.
DEPAC Instrumentation method is the most widely used form of precise measurement.................
The very common Digital Multi Meter (DMM) does NOT Use 'sampling' to provide 'readings' of Volts, Ohms, and Amps, etc. Why not??? It would be very suseptible to common 'noise' and give you erratic, meaningless readings that don't make sense. Instead all DMMs, from very cheap to the most expensive, use the same method DEPAC uses to obtain its quality, precise measurements.. This superior method is called syncronized averaging (also called dual-slope integration). This much better method does not require heavy signal filtering, like sampling requires, and so does not distort the signal. This 'smart averaging' is not suseptible to noise like 'sampling' and is able to provide true and steady readings that actually show what's really happening. Its also faster to get a true reading unlike heavily filtered inaccurate sampling.
'Sampling' is inaccurate, in the real world... The smart syncronized averaging used by the Common DMMs is not affected by 50 or 60 Hz powerline noise since the signal averaging period is precisely set to include whole numbers of 50/60 HZ periods. This automatically cancels the effects of this 'noise' on the measurements. A small signal can easily be seen accurately, and steady, even though there is significant power line and impulse noise. Sampling falls apart and will show very erratic readings. You only have to look at your Digital Multimeter (DMM) to see the precise DEPAC method in action in the real world.
DEPAC Method does not need to filter input signals (like A/D sampling requires) and results are not artifically smoothed. DEPAC results are True.. If the engine is running consistently, the results will be consistent and smooth. If the engine stumbles and is erratic then the results will also be erratic and not repeatable.. You need to see the truth and understand the results. All other system smooth the results to make a bad running engine look good (but is this acceptable?).
DEPAC Method is mathematically correct and uses pure statistics to process information. DEPAC system averages un-filtered information over whole numbers of engine cycles (2 revolutions for 4-stroke). This average is not affected by any periodic engine pulsing or related vibration. Mathematical signal averaging over whole engine cycles produces a True Average packet of information. The DEPAC process does not compromise the quality of the results. What you see is actually what happend, like it or not.
See below... Each DEPAC Integration, or Averaging, period is represented by a Machine Gun Dot (MGun). Each MGun dot 'shot' onto the graph screen below represent the actual Torque and Power (at RPM) of these averaging packets. At hi RPM these MGun packets are the true signal average over 12 revolutions (6 cycles). The next MGun packet holds average information over the Next 12 revolutions of the engine (and so on). The Pattern of MGun dots shows the statistical behavior of the engine. A smooth running engine will have a small, compact pattern of MGun dots. A bad running engine will have much more 'Scatter' showing the engine is stumbling (for whatever reason). As a Dyno/Engine tuner you need to see this True engine behavior.. Or, really, would you feel more comfortable with other dyno systems that show you only filtered, smoothed, and artifically consistent, 'pretty' results?...... DEPAC technology provide significant results and the ability to see the smallest changes in true engine performance.
More information... The Screen-dump above shows two sweep runs, one Up and the other swept Down of (green) Torque and (blue) Power. This is a NASCAR 350 Cup engine on a Stuska dyno. The averages are very close and show great detail from the subtle effects of the complex under-the-car exhaust system. The MGun dots are for the sweep up from 3000 to 9600 RPM. This engine has MGun dots showing consistent behavior. A Bad running engine would have MGun dots scattered much more and not be consistent. Our ADL Controls were also used for these consistent Sweeps Up and the Down at about 500 RPM/sec. NOTE: The average difference between the dotted markers is 0.02 Ft lbs or 0.004% difference. Real Precise Results you can learn from and believe. DEPAC can upgrade any dyno to advanced performance. Also please note that these Fast Up and Down sweeps that the inertia error is canceled, very precisely.
(Note: At very low RPM these MGun packets are averages over 2 revolutions, for consistency, and widen as the Speed increases as in 2, 4, 8, 12, 16 revs).
The A/D 'sampling' method Is in all the engineering textbooks and everyone thinks that is is the only way. Really?... This is an extrememly simplistic method that ignores the fact the nature is random. Sampling methods just does not work to effectively measure Real Nature which is naturally random. How many really believe their engine output is perfectly smooth, and the same everytime?. Excessive pre-filtering is required but still results are flawed.
The DEPAC method uses the most common method of measurement. The method is called syncronized integration. Even your simple digital multimeter (DMM) uses this method (calling it Dual Slope Integration) since it provides the best possible accurracy in a real world noisy environment.
Sampling is very confused when trying to measure naturally random 'real world' sensor data. Excessive signal filtering is needed try to overcome this problem but this does not help. Attempts to prefilter the signal just make matters worst, besides altering or distoring the actual signal over time.
Sampling works OK in high speed data recording to produce time strip-charts, or plotting signals on a time scale. You see this with On-board race car data systems (like Racepak and and others) using this high speed digital recording method.. This is the niche of sampling... The big mistake is trying to use sampling for everyday practical data measurements. It just does not work well at all for many very good reasons. There is a far better method to measure and display results from sensor signals, results you can believe.
Sampling implies being fast but when you need to use so much pre-filtering, it is not fast and does not provide accurate results, no matter how many bits of the A/D converter. Sampling is very susceptable to inpulse signal noise that happen while 'sampling' the noisy signal.
Sampling is used very little in practical measurements. It is simply and extension of the old 'read' the gauge and 'Write' down the reading seen. Most dyno sampling methods are no more sohisticated than what we call "read and print", just an inaccuarate extension of reading the jumping gauges.. Actually reading the gauges was better. The observer would average out the fluctuation needle and write down an apparent average.. We are certainly much smarter than sampling when 'reading the gauges'.
The premise of sampling is that only an occasional peek at the signal is all we need.. Give me a break. What about all the important stuff that happens between these scattered samples?? Sampling is like watching a time lapse security video playback. For a steady, nonchanging scene, it looks OK. If there is any motion then all you see are these jerky glimpses of what is really happening. These short video 'samples' lack any real imformation. But the premise of sampling is that's all you need. Sampling is not very good as compared to the proper methods for documenting dyno information.
The most used method in the world to measure sensor signals is NOT (inaccurate) sampling. The digital multimeters (volt/ohm/amp) you have do not use sampling.... They simply wouldn't work very well if they did.
Syncronized Integration (smart averaging) is the Most widely used method of quality instrumentation. DEPAC uses this best method and provides the best results using further statistical processing. Uncompromised DEPAC performance.
Work in progress - - - - - - please return as we make this simpler and more clear.....