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Capture Peak Strain Gage Fluctuation For Shotgun Chamber Pressure Measurement

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nctnico:
It says here that using a piezo test is the best way:
https://en.wikipedia.org/wiki/Chamber_pressure

It there a flat surface on the gun? If yes, you can stick a piezo disc like this:

on the outside. These come in many different diameters and will produce a signal that you can measure using an osciloscope without needing amplification.

TurboTom:
The piezo you suggest will detect acceleration or dynamic deformation (warping) of the piezo's brass disc (in this example that is), but there's no way you can analyze an elastic deformation of another construction component in a quantitatively accurate manner.

The strain gauge approach is much more accurate and reproducable since the strain gauge is inherently calibrated and adds much less weight / inertia to the test setup. Moreover, accurately bonding the strain gauge to the exterior of the chamber is way less troublesome.

The piezo may do as a trigger element for pulsing the strain gauge's bridge excitation voltage if that's necessary, but I'ld not recommend it as the measurement transducer itself.

Silver_Is_Money:

--- Quote from: nctnico on December 17, 2023, 05:43:01 pm ---It says here that using a piezo test is the best way:
https://en.wikipedia.org/wiki/Chamber_pressure

It there a flat surface on the gun? If yes, you can stick a piezo disc like this:

on the outside. These come in many different diameters and will produce a signal that you can measure using an osciloscope without needing amplification.

--- End quote ---
Nothing flat on a cylindrical barrel.

David Hess:

--- Quote from: Silver_Is_Money on December 17, 2023, 04:54:33 pm ---
--- Quote from: David Hess on December 17, 2023, 01:57:00 pm ---I have done what you suggest but it was not with firearms.

Any digital storage oscilloscope can do what you need.  You may need several tries to get the gain of the amplifier and trigger level adjusted properly.  Back when I did it, I used an analog storage oscilloscope although DSOs were available.

Besides mechanical issues, like delamination of the strain gauge because the peak strain is too high, the largest difficulty will be with the strain gauge amplifier because normally they are limited to lower bandwidths for performance and noise reasons.  This should not present a problem now because there are many modern fast low noise precision parts.
--- End quote ---

Is there a reasonably priced amplifier that you can recommend please?
--- End quote ---

Do you mean a reasonably priced integrated circuit amplifier?  In the past I used the LT1007 or LT1028 and built my own amplifier.

I never found a suitable amplifier that was already built.  Most are intended for lower frequency applications and have limited bandwidth to control noise, but I did not look very hard.

David Hess:

--- Quote from: TurboTom on December 17, 2023, 05:58:24 pm ---The piezo you suggest will detect acceleration or dynamic deformation (warping) of the piezo's brass disc (in this example that is), but there's no way you can analyze an elastic deformation of another construction component in a quantitatively accurate manner.

The strain gauge approach is much more accurate and reproducable since the strain gauge is inherently calibrated and adds much less weight / inertia to the test setup. Moreover, accurately bonding the strain gauge to the exterior of the chamber is way less troublesome.

The piezo may do as a trigger element for pulsing the strain gauge's bridge excitation voltage if that's necessary, but I'ld not recommend it as the measurement transducer itself.
--- End quote ---

I thought he was referring to piezoelectric strain gauges which have greater sensitivity than metal foil strain gauges.  I never used piezoelectric ones myself.

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