DIY Scope Pressure Transducer
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- Опубликовано: 21 июл 2024
- I have spent several years now working with pressure transducers on the PicoScope automotive platform. By no means do I consider myself an expert with these tools, but I really enjoy finding new ways to utilize them and better understand where they fit in the diagnosis of live automotive repair. Several years ago, I attended a seminar by faculty at Souther Illinois University at Carbondale. In that presentation, they highlighted experiments with affordable test equipment. I decided to take my own journey in setting up a $15 transducer to compare it to the ever popular, PicoScope WPS500x. In the end, the result is what most of us would expect, but for the. money. I think it opens the door to some good use cases where multiple sources of data need to be captured. Check out the link below for the sensor I used. Where would you see a use for this type of setup? Let me know in the comments below!
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Components in the video:
- 1/8" NPT 500 PSI Pressure Transducer - amzn.to/3yEVKMt
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SUBSTANTIAL Adam 's Analysis
Thank you very much for sharing what you know with us Adam 's Analysis
From Nick Ayivor from London England UK 🇬🇧
Very good project to save a lot of money because Banggood sell a pressure tranducer for picoscope around $265. Thanks a lot Adam!
Thanks for the info!!
Thanks for watching!
on the last capture you were zoomed out when you took the pico transducer capture and then zoomed in to x4 then you took a capture with the cheap transducer while still zoomed in at x4. Think it would have giving the cheaper transducer a capture like the first cheap transducer capture and took away the step like waveform if took at 1x. Thank you for sharing and great vid
Good catch. I’ll have to see if I saved that waveform and check it out.
Cool project. Thanks for the idea for the USB. I almost stooped to buying a lab power supply. Instead I'm just going to use a USB portable battery (cell phone charger). I would recommend not plugging in the USB cord to the battery without first testing for shorts in the wire. If you short out a battery it might explode.
I've just had this same problem with the schrader valve,but i don't think the schrader valve can be taken out of the hose i have in the spark plug hole!So i'm stuck.
so the power and ground wires going to tranducer are what we tie out scope into,and just do nothing with signal wire?also how do i determine which pin on transducer uses the power and ground?im gonna guess the outside pins can be power or ground and middle pin is signal that we dont use is this right?
That cheap transducer is almost useless for in cylinder pressure. It completely missed the pocket after the expansion stroke leading up to the exhaust stroke on the running compression. There is some valuable information there. Some $75 Honeywell transducers do very well if you’re looking for something decent without having to get a WPS500. The price is worth it for me but I’m also a diagnostic tech that uses it regularly.
Thank you for the insight!
The output of the transducer is an analog voltage which is instantaneous. It is the Picoscope that decides what the refresh rate is. I don't own a Picoscope, but there must be some way of changing the refresh rate on it.
Another thing I just thought about. You are using a 500 PSI sensor; so you are using less than 1/5 of the resolution. The voltagge range for that transducer is 0.5 - 4.5V and you are measuring a low of less than 0.5V and a high of only 0.9V. I don't know what the Picoscope uses, but I'm going to guess that it is a lot less. I would try it with a 100 PSI transducer, just to see what would happen.
Thanks for the feedback, these are all great points!
@Adam's Analysis I've seen these same transducers used elsewhere and they seem to do ok. I'm not sure I've seen one on a running compression test. At any rate, Lizard King is correct that the cheap transducer outputs analog. It is the pico which uses ADCs (analog to digital converters) to convert the analog into a digital waveform. the pico has quite high end ADCs and has a "refresh rate" (sample rate) of up to a billion times a second. Those two things will determine how accurately it can capture (quantize) that analog waveform. Note that in this capture you only have it set to 1MS/s a.k.a. 1,000,000S/s. I do not see any place on screen that shows the resolution it's using (up to 16-bit), but the key is to look at the window in the upper right: it shows the "zoomed out" waveform and the waveform looks normal there.
How to convert Voltage to bar with a cheap transduces? Any link? Thanks.
Great video. But the stair step pattern you see is of the settings on the scope software and not the transducer. The transducer device is analog and therefore it doesn't update. It's a continuous signal. I tried it with a cheap Ebay transducer and the patterns were identical to the WPS. No Stair step effects.
Thanks for the feedback!
This depends a lot on the transducer. You can clearly see Adam's waveform has a time-based step in it, rather than a amplitude-based step.
Most of these sensors have ASIC chips inside them. They're not as simple as they seem. These ICs allow for error correction, and compensation for non-linearities or temperature drift. As such, they have response times. Check out a datasheet for a Kavlico P265, for instance (15ms response time listed). I'm not sure how these ASICs are built, but they could be largely analog still. Response times are alluded to more like a slew rate than a sample rate, so perhaps they wouldn't give these stair steps after all. Even so, with a 15ms response time, there would certainly be some waveform distortion even if it weren't obvious stair steps.
If you found an affordable sensor with a quicker response time, could you provide a link or provide a recommendation? I'd love to find one myself. It seems to be a crapshoot, with many sellers even mislabeling the full-scale ranges, so customers end up with poorer resolution than they'd hoped.
@@CheapskateGarage That it correct. I recently heard that these transducers have a chip in them that interprets the analog data. That makes sense of this stairstep pattern. I would like a faster transducer, like the pressure transducer made by Pico. It doesn't have the stairstep pattern.
@@cyberslacker5150 I actually just found a great video that dives a little deeper making these comparisons:
ruclips.net/video/uan5mgi2mgw/видео.html
I may pay a bit more for a Honeywell or SSI sensor now.
So your samples per second rate was the same? I would have never guessed that the cheap transducer would produce a stepped output like that. I figured it would simply be a continuous (smooth) analog output.
I believe the refresh rate of that cheap transducer is slow enough that we can see a stepped output.
Excellent narrative! Did you ever try to find a quality pressure transducer that's comparable to the Pico? Also, what do you use for testing both + & - pressure in the same transducer?
Thanks for watching! I have not gone searching for a better transducer. We are fortunate to built up to four WPS500x kits to use with our students. As for getting both vacuum and pressure, that would likely be a more unique and more expensive transducer.
@@AdamsAnalysis
OK, thanx.
I have a map sensor from an old Horizon I'm going to test out today. Maybe that'll work?
Thinking of trying this with a 10bar map sensor. Is there anyway to convert the voltage on the pico software to display psi?
The picoscope software has an option for "Custom Probes" I'm not sure if PSI is one of the options. I'll have to take a look.
Absolutely. Pico custom probes is very flexible.
Hello, I'm Brazilian and I didn't understand this transistor very well, does it work well for gasoline engines or not? does it measure atmospheric pressure? I'm looking to buy a transducer to use on my hantek oscilloscope, thanks
This transducer did work well overall given the cost and would provide some useful information for diagnostics on a gasoline engine. If I was to invest more time with it, I think I would purchase some quick release fittings and cut down on the amount of flexible rubber hose. I would also work on building a custom probe profile in the software. I've got a Hantek scope that I have hardly used. I should give get that going and refine the DIY transducer a bit.
Can i use pressures transducer for diesiel engine ?
You certainly can, it is just important that you verify the rated compression specification for the engine and make sure it does not exceed your transducer. PicoScope for example sells the 500 PSI rated transducer for petrol engines and a WPS600c which measures up to 600 bar (8700 PSI).
use linear PSU for 5V ! Or battery !
can you give the diagram how to make the connection
USB cables generally have a red (5v) and black ground. The other two (green and white) wires are communication. I used the red and black from the USB to power the transducer. I can't recall what the colors were, but I made those connections then the signal wire from the transducer was the input for the scope signal. Hope that helps!
@@AdamsAnalysis can you connect the red and black wires of the transducer to a 12v battery post
Way too much hose you need a hard hose or braided steel paintball lines 8” from eBay etc then grab some 14mm adapters
Thanks for the suggestion! My setup was definitely experimental and in need of more refinement.
Slew rate