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DIY Pressure Transducer

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27 Apr 2018 08:10 #20238 by SailorBob
Replied by SailorBob on topic DIY Pressure Transducer
not sure why the ebay link isn't showing up....

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29 Apr 2018 10:45 #20305 by SailorBob
Replied by SailorBob on topic DIY Pressure Transducer
here's the final fix. I was able to clean up the signal on the 200 psi transducer enough that it's useful for work:

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01 May 2018 15:14 #20361 by Charles Acosta
Replied by Charles Acosta on topic DIY Pressure Transducer

SailorBob wrote: here's the final fix. I was able to clean up the signal on the 200 psi transducer enough that it's useful for work:


Can you do a cranking or running waveform?

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02 May 2018 04:22 #20370 by SailorBob
Replied by SailorBob on topic DIY Pressure Transducer
It's here in this other thread, I'll probably do a quick follow up video also:

www.scannerdanner.com/forum/post-your-re...i-at-idle.html#20351

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14 Sep 2018 09:31 #23312 by Sooknanan
Replied by Sooknanan on topic DIY Pressure Transducer
Anyone knows if a DIY pressure transducer will work with the Pico Diagnostics Software, doing a compression test.

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15 Sep 2018 13:51 #23337 by SailorBob
Replied by SailorBob on topic DIY Pressure Transducer
Yes, it will work fine. A scope is a scope. I'm using my homemade transducer with a Pico 2204A. Just set up a custom probe with low pass filtering enabled at 1 kilohertz and you'll get a good clean waveform.
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16 Sep 2018 23:26 #23364 by Sooknanan
Replied by Sooknanan on topic DIY Pressure Transducer
(null)
I know the diy pressure transducers will with the pico 6 software.
But what I am asking is if the pico diagnostics software would recognize a diy p/t while conducting a compression test and populate for each cylinder.




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17 Sep 2018 01:51 - 17 Sep 2018 02:14 #23365 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic DIY Pressure Transducer

Sooknanan wrote: (null)
I know the diy pressure transducers will with the pico 6 software.
But what I am asking is if the pico diagnostics software would recognize a diy p/t while conducting a compression test and populate for each cylinder.

Sent from my iPhone using Tapatalk


But pressure sensors aren't used for relative compression tests they are done be either an amp clamp on the starter cable or by the battery voltage method. The Pico software should have no problem with working on battery cranking voltage to give a measure of starter current.








From the Pico Automotive Website

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Last edit: 17 Sep 2018 02:14 by Andy.MacFadyen.

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17 Sep 2018 21:06 #23380 by Sooknanan
Replied by Sooknanan on topic DIY Pressure Transducer
Sorry for beating this to a pulp, last video you posted from 3:50 onward, they said the relative compression test can be changed to an absolute compression test by connecting the wpx transducer to channel B, so what I am trying to find out is, would this work with a DIY pressure transducer. I mean wouldn't you prefer see a pressure value for each cylinder rather than seeing a percentage.

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18 Sep 2018 03:57 #23382 by SailorBob
Replied by SailorBob on topic DIY Pressure Transducer
You can do a manual calculation of volts per psi by measuring actual compression in a single cylinder, then dividing that by the peak voltage ( after low pass filtering ) for that same cylinder. Here's a video about it:

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18 Sep 2018 07:30 #23384 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic DIY Pressure Transducer
Probably better just to make judgement call on the raw oscilloscope cranking trace, if one hump more than say 20% down you would want to do more tests anyway. Personally unless I suspect a valve rocker or cam lobe issue I would go straight for an old style cylinder leak down test.

One thing to be aware of with cranking voltage compression testing is old style starters tend to have much higher current draw than more modern starters which can be both geared and be the permanent magnet type.

Other thing to watch for is the number of cylinders --- 3 cylinder 4 strokes :-( always have odd looking cranking voltage traces, 4 cylinder engines have noticeable high peaks and lower valleys than 6 or 8 cylinders and of course on diesels the much higher compression pressures puts huge loads on the starter.

"It is the nature of every person to error, but only the fool perseveres in error." Marcus Tullius Cicero
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06 Oct 2018 15:57 #23707 by bruce.oliver
Replied by bruce.oliver on topic DIY Pressure Transducer
I can't get my DIY transducer to put up a clean waveform on my pico. The waveform is very "notchy." Ive made several adjustments to the settings but it stays notchy. But it does work, I diaged a plugged cat with it last week on a F150. Can't find the waveform, so I must not have saved it. Thinking about just buying the WPS next week

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06 Oct 2018 17:08 - 06 Oct 2018 17:10 #23712 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic DIY Pressure Transducer
If by notchy you mean you can see distinct steps in the trace it would suggest the sensor is mis-matched to the range you are measuring. For a running compression test a zero to 200 psi works well. The one below was made with a zero to 300 psi sensor. Also of course switch the connection wires to either a twisted pair or co-axial BNC as close as possible to the cylinder. On the scope settings make sure peak detect is turned off.


"It is the nature of every person to error, but only the fool perseveres in error." Marcus Tullius Cicero
Read more at: www.brainyquote.com/authors/marcus_tullius_cicero



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06 Oct 2018 17:38 #23714 by bruce.oliver
Replied by bruce.oliver on topic DIY Pressure Transducer
Well I will have to do some more testing. I have a 100, 300, and 500. I think I've been using the 500

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07 Oct 2018 04:28 #23725 by SailorBob
Replied by SailorBob on topic DIY Pressure Transducer
Set the pico to use 1 khz low pass filtering and that should clean it up. You're just seeing electrical noise probably.

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07 Oct 2018 07:17 #23726 by bruce.oliver
Replied by bruce.oliver on topic DIY Pressure Transducer

SailorBob wrote: Set the pico to use 1 khz low pass filtering and that should clean it up. You're just seeing electrical noise probably.


It's not noise. I am used to seeing that on waveforms. It's like Andy described, distinct steps in the waveform. Like the transducer responds to slow for the software.

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07 Oct 2018 08:06 #23727 by ShaoLin68
Replied by ShaoLin68 on topic DIY Pressure Transducer
Dont forget, in order to calculate your readings properly, 0.5v = 0 psi and 4.5v = whatever psi transducer you are using..

I am making a dedicated set of transducers myself that will be able to be used with either a pico or a verus..
15psi for Vacuum (which converts to 30 in Hg, which is what a regular vacuum gauge reads anyway),
150psi for fuel pressure (a fuel pressure gauge goes up to 140psi),
300psi for Gas engine compression (which is what a regualar gauge goes to),
and a 1000psi for Diesel engine compression (which is what a diesel compression gauge goes to.. Im a truck driver, I had to make one for trucks.. LOL)

over the Thanksgiving holiday, I am going to build the ones I have the stuff for so far.. for the electrical, I am using battery power/ground, then going to a 12v/5v stepdown to supply the transducers with the correct voltage.. there will be an LED at the power plug to let you know there is power, and an LED at the signal out to let you know there is signal going to the scope..

I will then post some videos showing them, and showing how to use them so you get the best results.. I dont have access to a verus but I will be testing it on a Hantek 1008C.. I have a 98 Infiniti I30 that will be my test mule..

but that wont be for another month and a half.. I just wanted to point out that the transducers use a 5v and produce a 0psi reading at 0.5v and maximum psi reading at 4.5.. have a good day..

heres a sneek peek at the labels..
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