Computer program that shows p-p voltage?

[Matt]

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

 

[Rich Webb]

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?

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.
http://www.dataq.com/194.htm
http://www.measurementcomputing.com/cbicatalog/cbiproduct_new.asp?dept_id=352&pf_id=1535

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.

 

[Matt]

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

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?

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.

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!

 

[Rich Webb]

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?

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.

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?

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.

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?

Basically, just flip the diode.