Newly re-made pressure pulse sensor

As requested, shots of the second pressure pulse sensor I (badly) made.



It sure is ugly, but it works! :lol: The piezo disc is glued to the bottom of this contraption. Parts courtesy of Digikey and Lowes.



I have NO idea if this matters, but I opened up the bottom so the bottom of the disc is open to atmosphere. I like to think it'll result in more sensitivity? Could be BS. :silly:

Got some waveforms off a known bad Olds Cutlass. I *think* I'm looking at a bad exhaust valve? Positive voltage is vacuum, negative is pressure.

Can you explain this, please? I'm not sure if I know what I am seeing. This is intake vacuum? In-cylinder pressure?...using the piezo disk as a pressure transducer?

The positive being vacuum and negative being pressure is throwing me off, too. Can it be inverted?

pole71 wrote: Can you explain this, please? I'm not sure if I know what I am seeing. This is intake vacuum? In-cylinder pressure?...using the piezo disk as a pressure transducer?

The positive being vacuum and negative being pressure is throwing me off, too. Can it be inverted?

Well I have the same questions Tell us Tyler.

I wonder what kind of pressure this can handle before the crystal cracks and is unusable. And, honestly, I do not think it is ugly. I think it's a great design. Compact. Has banana jacks built in. And, if you lose it or it breaks it was inexpensive and easy to remake. Great job.

You can invert it on screen or just reverse the wire polarity ---

EricGoodrich wrote: I wonder what kind of pressure this can handle before the crystal cracks and is unusable. And, honestly, I do not think it is ugly. I think it's a great design. Compact. Has banana jacks built in. And, if you lose it or it breaks it was inexpensive and easy to remake. Great job.

The disc is quite thin the problem with over under pressure is permanent bending of the disc. The main problem I found with mine was the wires coming off. In the end I bought an off the shelf Auto Ditex one which wasn't overly expensive. autoditex.com/pressure-pulse-sensor-63.html

pole71 wrote: Can you explain this, please? I'm not sure if I know what I am seeing. This is intake vacuum? In-cylinder pressure?...using the piezo disk as a pressure transducer?

The positive being vacuum and negative being pressure is throwing me off, too. Can it be inverted?

Sorry for the lack of info. :blush: It's intake vacuum pressure pulses during cranking, using the piezo disc inside the plumbing fittings. The scope trace can definitely be inverted depending on personal preference. I've just come to think of vacuum pulses as 'good', and lack of pulses or pressure as bad. As far as these waveforms go, anyway.

I wonder what kind of pressure this can handle before the crystal cracks and is unusable. And, honestly, I do not think it is ugly. I think it's a great design. Compact. Has banana jacks built in. And, if you lose it or it breaks it was inexpensive and easy to remake. Great job.

Thanks!

The disc is quite thin the problem with over under pressure is permanent bending of the disc. The main problem I found with mine was the wires coming off. In the end I bought an off the shelf Auto Ditex one which wasn't overly expensive. autoditex.com/pressure-pulse-sensor-63.html

Yeah, I figured the same. I think its use is best restricted to cranking vacuum/crankcase/exhaust stuff.

I see the Auto Ditex one can be had for around $100 - WAY more reasonable than the $400 they want for the First Look.

Also, I was an idiot and had the firing order wrong on the overlay. :blush: :silly: How did I forget the Chevy firing order? Let's try this again:



Now I wonder if it's an intake valve? :huh: It left today, so I may never know.

What does the yellow channel represent?

The yellow is from the pulse sensor, connected to the brake booster hose on the intake. I'm believe I'm looking at a missing vacuum pulse from the #5 cylinder.

If it helps, this is a known good capture off a four cylinder:



All pulses are even and relatively uniform. This next one is with a loose plug. You can see the variance in the peaks of the pulses.



Then I took the plug out completely.

Andy.MacFadyen wrote:

EricGoodrich wrote: I wonder what kind of pressure this can handle before the crystal cracks and is unusable. And, honestly, I do not think it is ugly. I think it's a great design. Compact. Has banana jacks built in. And, if you lose it or it breaks it was inexpensive and easy to remake. Great job.

The disc is quite thin the problem with over under pressure is permanent bending of the disc. The main problem I found with mine was the wires coming off. In the end I bought an off the shelf Auto Ditex one which wasn't overly expensive. autoditex.com/pressure-pulse-sensor-63.html

Good find. Have you used it much?

One thing I've learned about peizo discs is that they only generate voltage when their momentum is changed. If you vibrate them or flex them they generate voltage. If you apply steady pressure they will generate voltage as the pressure is rising but once the pressure is held, and stops rising, voltage will bleed off. I have found the bleed off rate to be about 200ms.

I've also found that their response range for sound tops out around 3khz. After that the voltage generated drops off rapidly. This was tested by using the mic to pick up sound vibrations in air. Impacts will always be picked up. For example using these for detecting knocking in engines. But steady frequencies above 3khz are a problem.

These things still kick ass though and I'm always finding new ways of using them.

I bought a bag full of mics off Amazon so I figured I may as well use them for something. So, I made three of these...

Here are all the parts I used. No glue for the disc. I used the step inside a 3/4" coupler and a rubber washer to make a seal. The bottom is open to atmosphere.

The next few photographs illustrate how is assembled.

The step inside the coupler...


Rubber washer for the disc to sit on ...

The disc sits between the end of the 3/4" pipe and the rubber washer. The notch is for the wire soldered to the disc.

One half assembled with the cap ready to go on. The wires have knots to prevent them from being disconnected from the disc if they get yanked on.


And that's it. Now to use it. I'll post some updates soon. First thing I plan on doing is sampling the same thing on three channels ( I made three of these ) and compare them for consistency.

I wonder why some pictures are getting rotated when I upload them. It seems to be random...

Here is what I did for some experimentation. I plugged all three sensors into the side of a 2 liter bottle.

First, I pressed on the side of the bottle, rapidly and with increasing pressure and then decreasing pressure just to get an idea of how consistent they are to one another. Two of them are nearly identical while the third generates a waveform with slightly less amplitude. Still, all three create useful signals.



Next, I pressed and held, waited a moment and released. As you can see, there is a wave when the pressure is increased and held and there's a second wave when the pressure is released.


Now, just one quick press and release. Pressure rises and falls back to zero immediately. Unlike a MAP sensor, or any three wire pressure sensor, the mic is not generating a steady signal based on pressure. The mic is generating voltage as the material is deformed. This is really important because the pulses generated are not going to look like a powered sensor looks. These peizo sensors will generate a sin wave with each pressure pulse. Measuring exhaust pressure pulses, for example.

Still, awesome, cheap and effective. I'm just going to have to practice with them so I know what the hell I'm looking at.

It's also important to understand that polarity matters. My sensors generate a negative voltage on initial pressure increase then a positive voltage on pressure decrease. If you're using more than one, say to check exhaust pressure and intake pressure at the same time, if the sensors aren't polarity matched the signals will be 180 degrees out of phase. If you aren't careful this could possibly get you in trouble.

This is an example with one sensor having reversed polarity. ( Plugged in backwards, ie red/black wires etc )

Dude the soda bottle test is awesome. I honestly hadn't considered using multiple pressure pulse sensors before, but it makes sense! Crankcase, intake, exhaust, plus some kind of sync, and you'll definitely know where the issue is.

I recently adapted a Stant cooling system pressure tester cap to work with my pressure transducer for checking headgasket leaks. I'll post a picture as soon as I go back to work Monday.

I repeated the same test with the soda bottle except this time I included a WPS500x pressure transducer for comparison. The black trace is the WPS500x

I wouldn't substitute my WPS500x pressure transducer for a peizo sensor but for less than five bucks these peizo sensors are definitely worth it. Next I'll sacrifice one of them to see how much pressure/vacuum they can take before the disc fails.