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Home made in cylinder transducer

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17 Jul 2020 13:21 - 17 Jul 2020 13:24 #41381 by Noah
Replied by Noah on topic Home made in cylinder transducer
I'm wondering if I can power it from the auxiliary port on the top of the Verus where the Snap On transducer would get its power and ground. Then maybe I could get a good calibration and use the PSI scales.
I'm pretty sure the Snap On transducer and the one I am using are both 500psi.
I think I have 2 secondary rpm pick-ups collecting dust, I may try to cannibalize one....

I definitely need to do more testing to be able to translate the voltage scales to actually pressure and vacuum.

I will continue post here as I experiment, thank you for your input. It is greatly appreciated!

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Last edit: 17 Jul 2020 13:24 by Noah.

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17 Jul 2020 18:01 #41386 by Matt T
Replied by Matt T on topic Home made in cylinder transducer
Google found this which has pin-outs in the pdf attached to the first post. One interesting thing is that the aux port 0V is floating relative to the 'scope ground. Makes me wonder if maybe the 'scope does something in transducer mode to filter out any voltage changes between aux 0V and ground. Might switch that channels ground over to 0V or something??

Also if the aux 0V floats there's a good chance the USBs will too. Something else to bear in mind if you're unable to get a consistent DC reading at atmospheric pressure. I wouldn't tie the 'scopes 0V to 'scope ground but powering the transducer with a wall wart and tying it's 0V to the 'scope ground shouldn't cause any problems. Or at least not any expensive ones :lol:

www.scannerdanner.com/forum/diagnostic-t...sure-transducer.html
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18 Jul 2020 08:02 #41391 by Noah
Replied by Noah on topic Home made in cylinder transducer
I forgot all about that thread!
Thank you once again Matt, owe you a beer :)

I found the utility in Windows to test various functions of the scope, including the 5v power supply on the aux plug and was able to ID power and ground. I intend to re-pin the Snap-On rpm pick up too utilize it to power the transducer.

Mine isn't power all the time, so I don't know if it powers on when you select an appropriate test lead preset for a given channel or how it works yet.

I Also want to try a "wall wart" as you call it to see if it skews the 0 line compared to the USB ports on the Verus.

I downloaded the PDF and gave it a glance but I will give it a thorough read through this afternoon.

Once again, thank you very much!

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22 Jul 2020 18:35 - 22 Jul 2020 18:35 #41520 by Noah
Replied by Noah on topic Home made in cylinder transducer
Paul, I can't seem to get this to work for me.
I repinned an rpm pick up for the Verus to supply power and ground to my transducer but the calibration fails every time and the pressure ends up skewed very negative.
I have a couple that output 0.5 volts at atmosphere and it still won't take.

Do you use yours on the pressure setting or volts?

Very nice build by the way. I need some kind of coupler to thread mine into a compression gauge hose.

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Last edit: 22 Jul 2020 18:35 by Noah.

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22 Jul 2020 18:40 #41521 by Paul Marchant
Replied by Paul Marchant on topic Home made in cylinder transducer
Pressure mode on the Verus and on the Vantage Pro, and it works every time.

So, some faultfinding is in order.

With the back removed from the d-type, plugged in to the diagnostic tool, with the pressure sensor soldered on, what voltages do you see on the relevant pins (as per the crap picture in my documentation)?

The Verus seems to expect a transducer that outputs 0.5 to 4.5v, with 0.5v for zero PSIG. When it does the 'calibration' thing, it's assuming that the transducer is electrically connected, but with zero pressure on it. This voltage is then deemed to be zero PSI by the Verus / Vantage Pro and 4.5v is full-scale (i.e. 500PSIG if you're in 500PSI sensor mode).
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22 Jul 2020 19:02 #41522 by Matt T
Replied by Matt T on topic Home made in cylinder transducer
For adapting the transducers to a gauge hose do you know what thread diameter and pitch they are? And whether they're taper seal like a pipe thread or use a gasket or o ring?

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22 Jul 2020 19:05 #41523 by Paul Marchant
Replied by Paul Marchant on topic Home made in cylinder transducer
Thinking back to when I built mine, both the transducer and the remains of the compression gauge kit were 1/4 NPT tapered thread. I just did the usual two wraps of PTFE plumber's tape that I do when fitting couplings to air-tools and it sealed up fine.
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23 Jul 2020 08:26 - 23 Jul 2020 08:29 #41528 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Home made in cylinder transducer
A lot are 1/4" Gas thread (more or the same as 1/4" BSP) as used on shop air compressors there is also a tapered version of this thread BSPT.
1/4" Gas looks very similar to 14mm spark plug thread but don't ever mix up the two types.

Also to clear up terminology a transducer is different from a sensor a sensor requires external power, a transducer dosen't require power it is two wire and generates its own voltage.

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Last edit: 23 Jul 2020 08:29 by Andy.MacFadyen.
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23 Jul 2020 09:40 #41529 by Matt T
Replied by Matt T on topic Home made in cylinder transducer
Aside from Brit and US pipe threads, which are different, there are also numerous other standard and metric threads Noahs transducers could be.

Andy.MacFadyen wrote: Also to clear up terminology a transducer is different from a sensor a sensor requires external power, a transducer dosen't require power it is two wire and generates its own voltage.


Three wire voltage output are transducers. 2 wire pressure transducers are usually 4-20 mA loop powered. I can't recall ever seeing one of those on a vehicle but they're the most common type for industrial process control.

www.omega.com/en-us/resources/pressure-t...cers-troubleshooting

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23 Jul 2020 17:56 - 03 Aug 2020 21:46 #41555 by Noah
Replied by Noah on topic Home made in cylinder transducer
The threads are small? Lol, not my bag. I never invested the time to learn threads...

I did find a brass coupler to marry it to my compression gauge but I think I'm abandoning the refrigerant pressure sensors.
The voltage output at rest is too low to use the pressure scale on the Verus. I ordered the same one (presumably) that Paul has had success with. The seller claims it to have a range of .5-5 volts.
All mine put out .012 at rest.
If faced with the prospect of spending several hundred dollars on a transducer set up, you better believe I'd just live with this setup on a 2v scale, measurement be damned. But for under $20, I'll give this a try.
Thanks for your help guys!

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Last edit: 03 Aug 2020 21:46 by Noah.

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31 Jul 2020 19:09 #41885 by Noah
Replied by Noah on topic Home made in cylinder transducer
The 300psi sensor came in today. Hopefully there won't be too much work waiting for me Monday to try it out;)

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03 Aug 2020 21:39 #41997 by Noah
Replied by Noah on topic Home made in cylinder transducer
The first testing with the new sensor is a bit disappointing. When compared to gauge pressure it is 5psi off (positive) around 5 psi and deviates proportionally as pressure increases. So 80psi gauge pressure is more than 100psi on the scope scale.

Looks like a proper 500psi & 100psi sensor is in order to properly use the pressure scale.

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04 Aug 2020 11:11 #42003 by juergen.scholl
Replied by juergen.scholl on topic Home made in cylinder transducer
Is the sensor's update rate fast enough to deliver a good enough, not chopped waveform?
I got frustrated when playing around with these sensors because of the deficient resolution.

Could you upload a screenshot, please?

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04 Aug 2020 14:46 #42005 by Noah
Replied by Noah on topic Home made in cylinder transducer
I never installed it in an engine after the bench test results were not favorable, but I should have something here at the shop I can get a waveform from and post it up.
It did seem to respond appropriately while changing the air pressure through my cylinder leak down tester, but obviously the changes taking place were not happening nearly as rapidly as inside a running engine.

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04 Aug 2020 19:21 #42008 by Matt T
Replied by Matt T on topic Home made in cylinder transducer
For bench testing mine first I used a hand pump to confirm it would measure vacuum. Then threw together an airline quick connect Tee with a short hose from it to the transducer. Then hooked it up to a couple air hammers. The faster one is 4,500 BPM and the slower 2,500 BPM IIRC.

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04 Aug 2020 20:52 - 04 Aug 2020 20:55 #42011 by Noah
Replied by Noah on topic Home made in cylinder transducer
That's a pretty good idea to measure it's response, thanks Matt :)

I put it into my Ridgeline but unfortunately got occupied with visitors.

It did look like the sensor output at shorter time samples was choppy and not fluid, almost pixelated, but I was distracted. It could have been me...

After the clean captures from the salvaged refrigerant pressure sensors, I fully expected to see similar, nice, smooth transitions....

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Last edit: 04 Aug 2020 20:55 by Noah.

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05 Aug 2020 19:00 #42022 by Noah
Replied by Noah on topic Home made in cylinder transducer
The sensor seems to have been damaged. It now outputs 1.5v at atmosphere and will not calibrate to use the voltage scale built into the Verus.

I do still have access to the Accord by the way. It's out in the yard with no tires, I just haven't had the ambition to go out there pull the head.

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