# Computer program that shows p-p voltage?

• posted

I'm doing work with some accelerometers on a vertical oscillator, and want an easy way to gather the data. They put out a voltage proportional to the acceleration, and I'm looking for the peak to peak voltage, to find the greatest acceleration. I can hook it up to a sound card, but have not been able to find a program that will show me the p-p voltage (they all show dB levels, even on a FFT). I know some Java, but don't have the know-how to write my own. Any ideas? Am I even posting in the right ng? TIA! Matt

• posted

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Determine what voltage corresponds to 3dB by inputting a signal
(within the bandwidth limitations of the card) which drives the```
• posted

Wouldn't peak to peak be the greatest change in acceleration and not the greatest acceleration?

Regardless, are you *only* interested in the peak values or also in the instantaneous acceleration? If the former, then an appropriate op amp "peak hold" circuit might work, with the value then read using any inexpensive data interface; a multimeter with RS-232, or a small Dataq or Measurement Computing device.

If you need a higher sample rate then you're looking at more specialized equipment or "rolling your own" with a buffer amp and a microcontroller.

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Rich Webb   Norfolk, VA```
• posted

There's a nominal voltage of ~1.2 V, and the voltage varies about 23 g/V (.043 V/g). So, the peak to peak will give the difference between the two extreme accelerations (it's vibrated vertically). If the p-p is 1 volt, then it's experiencing ~11.5 g's each way, right? This is in the 20 - 2000 Hz range. I think I will try the calibration exercise suggested in the above post (putting in a known p-p, then doubling it and seeing what that does to the dB's). Will having a wave that isn't sinusoidal adversely affect this?

How would I design an op amp "peak hold" circuit? Am I correct in assuming this would simply hold the peak voltage, so I could measure it with a multimeter? I would then have to assume that the variance from the nominal voltage was symmetric both above and below that nominal voltage (I don't think it would be - it would be 1g higher on the positive side, right?). Is there a way to design a "trough hold" circuit that would hold the _lowest_ voltage? Thanks for the help!

• posted

Only if it's symmetrical. If it changed direction more slowly on one end of the travel than on the other it will still be moving back & forth but the acceleration wouldn't be the inverse.

Google for { "op amp" "peak hold" } for some ideas. You'll probably want some amplification in any case, so peak hold circuit followed by a modest amplification stage might work.

A multimeter would work to measure the result.

Basically, just flip the diode.

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Rich Webb   Norfolk, VA```

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