Guys, I have asked this question to everyone I know with some knowledge of a scope. Hopefully someone here can give me an answer. I have a 4425 pico. I also own various pressure transducers. Now, on the pico if you buy the wps system you can measure pressures and the scope will show the psi when you choose the option in the menu for the wps. However, I have tried my fluke pv350 which will give me a waveform, of course. However it will not be scaled correctly. So as an example, I did cranking compression on a 4.3 blazer today. The results were 16.5 psi, when of course the actual compression reading on a gauge was close to 175psi. Is it possible to set the pico up to use with other transducers besides the 1200 dollar kit they offer and get accurate pressure readings? If this is a stupid question I apologize, but I have no one who can help me out and it is frustrating. Any input is appreciated as always.
Also while I am on this subject, if I used the fluke and set it on a millivolt scale it read in the neighborhood of 150. This was closer to the actual compression in psi but is this just a coincidence? Or is there some sort of math formula to set the scope on a mV scale and convert to psi? I know so little it hurts...
"The man who says it cannot be done should not interrupt the man doing it."
Joe, reading other replies in threads I wont accept you know little at all.
A quick google tells me the WPS reads 1V per 100psi and the fluke reads 1mv per psi (.1V per 100psi) so if you simply multiply your result by 10 its accurate. I'm pretty confident that's correct.
Edit, just took the time for your last paragraph to get through my thick head. Yes, at 1mv per PSI, measuring in mv scale will give you an accurate PSI reading.
Thank you Matt for the kind words and the helpful reply.
Ok, so then I was correct in thinking that my 16.2 psi was actually 162 psi. Now what I want to know is this. Is there a way to make a custom probe for the pico to scale and correctly show actual psi as the wps would do.
Secondly, being that I have my own home made transducer setup as well using three different pressure transducers how can I find out what they are v/psi rating is? Third would be why the hell can I never find this info when I search google?
I try so hard to get information on this stuff but no one seems to want to share it, even among other techs. Paul did a great thing with this site bringing people together to learn and share. This is what it is all about.
"The man who says it cannot be done should not interrupt the man doing it."
What it sounds like you want is some sort of reverse attenuator. I have no idea how to go about that sorry. Doesn't sound impossible though. As for calibrating the rest what if you T into your shop air and se the fluke to set it to something definite lie 100psi. Then look at your other transducers and record the outputs?
This sight is great. I find it easy to get intimidated by far more knowledgeable people but I just chime in when Í think it may be some use. Theres always so much to learn. Im all for sharing information. Theres plenty of crappy cars out for us all to fix.
A general issue on measuring compression pressure is that the design of the adaptor between the gauge/sensor and the cylinder can make a big difference. Any volume of air in the pipe between the cylinder and the sensor and the cylinder reduces the effective compression ratio, the stiffness/lack of stiffness of the tube also has a similar effect.
With a cranked compression test with an ordinary compression gauge the position of the Schrader valve in the adaptor is important the closer to the cylinder the Schrader valve is the more accurate the result.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
matt.white wrote: Ah ok, so a solid brass push in adaptor might show 175 where as a wps500 on a rubber hose may show 10psi less. Hadn't considered that.
Yes --- especially with modern high compression engines it didn't matter much with Flathead engines which were about 7:1 compression ratio , my own car is a 10.5 and GDI's are going over 11:1
I crunched some numbers on MS Excel for a 1.8 4 cylinder engine 450cc per cylinder with a 10:1 compression ratio.
I will do a calculation in PSI & Bar but I will need to revise the maths first. :silly:
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Thanks guys, I was aware of the hose/valve design effecting output on the scope.
On the pico they give you the ability to make what are called custom probes. So for instance when you attach a current probe , you tell the scope that you are using a 600A clamp from the tool menu. If you know how to do it, you can add your own custom probe, in my case a pressure transducer of a specific value into the menu for use at any time. However, I am simply not informed enough to do this. I have visited autonerdz, but they have certain things on the forum locked unless you either bought the pico from them or pay a 650 dollar a year fee for information. So, I am looking at other avenues of knowledge. Seems that the pico has the ability to do wonderful things in the right hands...I'd like to have a set of those hands if possible. lol
"The man who says it cannot be done should not interrupt the man doing it."
With the standard industrial 0.5 to 4.5v sensors I looked into making read directly building a circuit with a device called an OP Amp but the circuit design was beyond me I found the easiest way is just to read the pressure off a graph.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
I have been planning to, just haven't had a lot of time lately. We recently moved to the new location and it has been a rough transition. I had a few videos saved to edit, but decided that they were not worth posting up. Maybe I should have posted them...
"The man who says it cannot be done should not interrupt the man doing it."
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