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Capture Peak Strain Gage Fluctuation For Shotgun Chamber Pressure Measurement
Silver_Is_Money:
Would a Digital Oscilloscope be capable of capturing and storing an image of the brief fluctuation in the amplified DC voltage witnessed across a Wheatstone Bridge for the case of a Quarter Strain Gage glued above mid-chamber of a Shotgun? Or would some other instrument be better suited to the capture of this image, or at the very least the capture of the brief peak of the strain induced voltage increase witnessed upon firing the Shotgun?
Stray Electron:
I can't give you a straight answer to that but I would say that it's going to depend on the speed of the scope. They do make digitial scopes that are VERY fast, but FOR A PRICE. I also know that they do make systems that do what you want so it is possible but you would need a very fast censor and a fast scope. Just as, a rough estimate if you assume a muzzle velocity of 1000 fps and an 18" barrel and an initial velocity of 0 fps, the entire firing process would only take 3/1000 of a second. (That's assuming uniform acceleration but I think that the initial acceleration would be much higher.) And of course, the pressure rise would be even faster and you would want to sample that single pulse MANY times to get an accurate representation so you would need a very fast scope to accurately show the wave shape and not just the period.
But IIRC Brownells in Utah used to sell some kind of system to measure chamber pressure. I don't remember what kind of output device it had but it included piezo-electric sensors that were epoxied to the barrel.
tautech:
Welcome to the forum.
Certainly a DSO is a good tool for this task.
You would use a Single trigger setting at a trigger level and timebase setting to be sure to capture the complete pressure cycle.
Once captured export a BIN or CSV and import it into Excel to graph the pressure cycle.
TurboTom:
Virtually, any current digital scope would be fast enough for this job. Pressure buildup in the chamber will be in the low millisecond, maybe several hundreds microseconds range. Any entry-level DSO today will record a sample every nanosecond (1GSa/s) or faster.
The more problematic item in the signal processing chain is the strain gauge amplifier since the typical output voltage of the strain gauge is very low. Hence, often lock-in amplifiers with heavy low-pass filtering are applied.
Since the measurement itself will be very short and since the output signal of the strain gauge is ratiometric to the excitation voltage, you may consider pulsing the excitation voltage to a much higher value than the strain gauge would be able to withstand continuously, thus boosting the output level by that factor, and using a faster, low noise operational amplifier for signal amplification. Tests would be required to verify that this approach doesn't affect accuracy due to strain gauge heating.
For triggering the measurement chain, you could use either an optical interrupter type sensor to detect the cock approaching the firing pin (still many milliseconds to go...) or an accelerometer system that senses the vibration when the cock hits the firing pin (a few milliseconds before the shot will break).
...just some food for thought...
voltsandjolts:
@OP How do you plan to calibrate this measurement system, to get psi, or whatever?
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