All Springer/NP/PCP Air Gun Discussion General > Engineering- Research & Development
Trying to add pressure sensors to LDC testing.
WobblyHand:
--- Quote from: WhatUPSbox? on March 03, 2024, 03:46:59 PM ---
--- Quote from: WobblyHand on March 03, 2024, 02:34:14 PM ---I hesitate to say this, but could be interesting to apply an accelerometer or similar sensor to detect vibration of the LDC cylindrical body, sort of a ping detector. I'd bet it really rings.
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Yes, the hope is to integrate some of the other sensors into the set-up. If you look at the segment with the port for the pressure probe, there is a flat spot on the opposite side for either an accel or at least a contact mike. One thing I need to check is how sensitive the pressure sensors are to vibration. On one of the test shots I clipped the front cap and the sensor had a response.
The tricky part for me has been the data acquisition side. The pressure sensors have a sensitivity of about 3mV/psia. Unfortunately my 4 channel Rigol DSO only goes down to 10mV/div and is noisy at that setting. I don't want to spend the money (even surplus) for a lab instrumentation amplifier. I tried the AD620 based modules on Amazon but they had their own problems. I may try an authentic AD620 at some point. For now, I have a humble 2 channel hobby DSO that you see in the picture. It does have some useful features. It is battery powered and relatively low noise with a 5mV/div sensitivity and claims 12 bit. It also accepts an external trigger that I can trip with the laser gate. It will store and export 4 pairs of waveforms (1024 points). That's where the Excel plots came from.
As I add the mic/accel channels, those can go to the Rigol and share the trigger. I just have to make sure I avoid the EMI issues. I'm not an EE so this moves more slowly.
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Cheap decent data acquisition can be an issue. I have a two channel 200 MHz Siglent O-scope with a trigger channel that I bought a while back. It's great for the cost, but one always needs more channels. For multi-channel work, it might be worth rigging something up. Have to look around to see if there's any decent stuff out there. I'd think if all the channels were operating at 300-500 KHz it would be more than good enough. The question is always - how many are needed.
If you have circuit questions, let me know. I was a practicing EE for my career. Wasn't a full time analog circuit designer, but made more than my share of radar front ends for the automotive market. Quite a bit of cost pressure, but the job still needed to be done. We detected and tracked picowatt returns, including babies, strollers, children's toys, as well as vehicles. Anyways, it's an offer.
WhatUPSbox?:
Bruce, thank you for the kind offer. I may bounce a circuit concept or two off of you. Right now I'm trying to work through some EMI shielding/mitigation options. For the pressure measurements, I'm using battery power for everything (DSO, laser, and bridge excitation through a linear regulator). I use twisted pairs where possible and the noise is driven by the DSO and is a little over an equivalent psi p-p. When I add the acoustic sensors and the Rigol DSO, it will share the trigger circuit and I expect the noise to go up.
rkr:
To dampen the ringing on silencer shell a piece of bike inner tube or shrink tube on the outside is normally used. Neoprene covers also work if tight. In addition felt on the inside against the tube slows down the air before it hits the shell.
WhatUPSbox?:
So I already failed my first EE101 pop quiz. :-[
People should ignore the specific curves I included in the first post (though the barrel exit one is probably close).
I do need to add amplifiers between the sensors and the scope to provide isolation. I was OK when I was testing with just one sensor but with two (and the laser circuit), there is coupling with the bridge circuits because of the common ground.
I'll repost when fixed
WobblyHand:
--- Quote from: WhatUPSbox? on March 05, 2024, 03:38:53 PM ---So I already failed my first EE101 pop quiz. :-[
People should ignore the specific curves I included in the first post (though the barrel exit one is probably close).
I do need to add amplifiers between the sensors and the scope to provide isolation. I was OK when I was testing with just one sensor but with two (and the laser circuit), there is coupling with the bridge circuits because of the common ground.
I'll repost when fixed
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Sorry to hear that. It happens, especially if looking at small signals and big ones at the same time. I call it the "learning experience", aka school of hard knocks.
My radar chronograph front end was like that - kicked my butt for a while, until I got it. Was a seven stage active filter, and it took me a long time to design and debug, especially since the simulator just didn't take into account some real world things, like leakage currents. Actually it was the device models that didn't have those effects included. So you sort have got to learn as you go along.
Might want to consider differential amplifiers since they tend to be more independent of ground. You'll get there because you're motivated.
What specifically are you having an issue with? Got a schematic? Or some chicken scratchings?
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