Home made in cylinder transducer

The setup I have works really well, it's a 300psi transducer, and measures vacuum if the correct calculation is put into pico custom probe settings. I just need to figure out how to lower the setting by 2 psi. That's all

wrote:

The setup I have works really well, it's a 300psi transducer, and measures vacuum if the correct calculation is put into pico custom probe settings. I just need to figure out how to lower the setting by 2 psi. That's all
 

Try using a lookup table. Numbers I threw in are guesses for a 300 PSIA 0-5 V transducer. You'll have to adjust the voltages in the table to match your transducer. Also bear in mind that if you do have an absolute transducer the PSIG zero will drift around a bit due to changes in barometric pressure.

 

  This is the Linear equation I used for the 300psi transducer so I could use it for incylinder. That way I can see the vacuum pockets, it's just about 1.8psi off. I just need it to read zero at atmosphere. I can see incylinder waveforms with this equation great. I watched a video about setting the custom probes using a look up table with a 5 volt sensor, and it instructed to want to set your 0 psi at 0.5v and your max psi at 4.5v. Here's the video about that. I set my 80psi transducer by this and it compensates for atmospheric pressure I guess is the reasoning behind it

I'm still playing with these, just wanted to share an update for anyone interested.
Really my only complaint using salvaged pressure sensors is the lack of accurate voltage to psi scaling.
I recently discovered that the oil pressure sensor on Chrysler 3.6l V6 engines is just about a perfect 1-1 scale using the 100psi transducer setting on Snap-On scopes.
When bench tested against a trusted gauge I never saw more than a 3psi variance up to 100psi on the Verus Edge and Vantage Pro scope.
And, bonus, since I can use the transducer preset, now I can power the sensor with the appropriate AUX connector on the scope and not the USB port. (The aux power source is only switched "on" when selecting a preset that requires it, so on voltage scale the transducers need a different 5v power source)

I have changed a handful of the oil filter housings on these engines under the intake manifold (mostly Grand Cherokees and Chrysler 300s) and decided to harvest the pressure sensors.
It's a pretty common issue so chances are if you're in an independent repair shop, you'll have a chance to score one no charge.

Thank you Noah for this interesting update. Two questions here:

- Did you take a scope capture of both the pressure reading and the signal voltage as such at the same time?

- Do you happen to know the range/ max. pressure this sensor is capable; does it work with snap throttle acceleration reaching the 300 psi region?

I was looking for a picture to upload, but I guess I didn't save one. If I have downtime today I will post a picture.
I am however doubtful that it will be capable of reflecting pressure of the magnitude you mention.
I have yet to try it in a cylinder, but even if it's not an appropriate sensor for in cylinder testing, it will still be useful for other testing such as oil pressure and perhaps fuel pressure.

juergen.scholl wrote:

- Do you happen to know the range/ max. pressure this sensor is capable; does it work with snap throttle acceleration reaching the 300 psi region?

Since the sensor works with a 0-100psi scale it's probably putting out at least 4 volts at 100psi. It uses a 5V supply so the voltage isn't available to get anywhere near 300psi. The output will likely be clipped at 5V somewhere around 120psi.

I understand your reasoning. Voltage and pressure readings would confirm the sensor's operating span/correlation. It still may be the 100 psi range limiting a higher reading.

That was plugged into my cylinder leak down tester, from high pressure to low.
Max is about 100psi @ 4.5v
Min about 0.3psi @ 0.5v

Noah wrote:

That was plugged into my cylinder leak down tester, from high pressure to low.
Max is about 100psi @ 4.5v
Min about 0.3psi @ 0.5v

This confirms pretty much Matt's assumption about the operating range.


P.S. You really like this picture, don´t you?:woohoo:

lol, I'm more impressed at how easy it was to save a BMP right from the Vantage pro to a USB stick and upload the image.