OK, I have a 2bar MAP and want to use ac pressure sesnor..

[kp]

I used to run my wideband through the AC pressure sensor a while ago before all these fancy EIO interfaces but I'm kinda lost with this now. I liked the old calculated PID thing a lot better :)

I have a 2bar GM map sensor and I want to hook it to the a/c pressure sensor and use that to log boost. I already have two widebands hooked to the external voltage inputs.

So what I need is the 0-5v raw a/c pressure sensor voltage converted to display PSI.

here is the 2bar voltage out vs sea level pressure:

14.31psi - 4.90V
14.00psi - 4.84V
13.00psi - 4.67V
12.00psi - 4.50V
11.00psi - 4.33V
10.00psi - 4.16V
9.00psi - 3.99V
8.00psi - 3.82V
6.00psi - 3.47V
4.00psi - 3.13V
2.00psi - 2.79V
0.00psi - 2.45V
5.00inHg - 2.03V
10.00inHg - 1.61V
15.00inHg - 1.19V
20.00inHg - 0.77V
25.00inHg - 0.35V
29.10inHg - 0.02V

I can make minir corrections for voltage and elevation, I'm not looking for 100% accuracy, just run to run variation at the track. I can just log the voltage and convert it I know but it would be nice to have a direct reading in PSI :)


help

[Blacky]

There is a new "lookup" function for calculated PIDs for exactly this purpose.
The psi units are already defined in sae_generic.txt so don't redefine them in calc_pids.txt
You'll need to select the {GM.ACPS} Air conditioner pressure sensor voltage PID before this calculated PID will be valid. It's in the "Accessories " system.

Currently the lookup function is not interpolated, so you will get an output shaped like a set of stairs instead of a sloping line. Interpolation is being added to the next release.

NOTE: the line starting with "psi" and the line starting with "Lookup" should all be on the same line - the format is not preserved correctly inthis message.


# ================================================== ============================
# File details
# ------------
#
# This section defines various details about the file format.

*FILE

#Parameter Value Description
#---------- ---------------- ---------------------------------------------------
VERSION 7.1.1 File version
DECSEP . Decimal separator used in this file

# ================================================== ============================
# Units
# -------------------
# See sae_generic.txt for more information on the *UNITS section

*UNITS

#Code System Abbr Description
#-------- ---------- -------- --------------------------------------------------

# ================================================== ============================
# Add slot definitions here
# --------------------------------
# See sae_generic.txt for more information on "SLOT" formats
#
#Units Low High Fmt Expression
#------------ ------------- ------------- ---- ---------------------------------


*CLC-00-001
psi 0.0 30.0 .1
"Lookup({GM.ACPS},4.90,14.31,4.84,14.00,4.67,13.00, 4.50,12.00,4.33,11.00,4.16,10.00,3.99,9.00,3.82,8. 00,3.47,6.00,3.13,4.00,2.79,2.00,2.45,0.00,2.03,5. 00,1.61,10.00,1.19,15.00,0.77,20.00,0.35,25.00,0.0 2,29.10)"

# ================================================== ============================
*PRN - Parameter Reference Numbers
# --------------------------------
# See sae_generic.txt for more information on the *PRN section
#
#Code PRN SLOT Units System Description
#------------------------- ---- ------------ ---------------- ---------------- ---------------------------------

CALC.BOOST F500 CLC-00-001 psi Air "Boost via AC pressure sensor"

[kp]

cool, thanks Paul.

I'll try it tomorrow. I seen the lookup function but had no idea how to put in a calc PID format. For some reason I'm just not getting how to create calculated PID in this version - I just havent spent a lot of time on it..

If I were to want to do a correction, say multiply the voltage by like .95 or something how would I include that. Also to smooth out the line I could put more lookup points in I assume until the new version comes out. Any limit to how many?

Kevin

[kp]

Been trying to make it work for almost 3 hours - decided to do a search and found this:

http://www.efilive.com/forum/viewtopic.php?t=1717&highlight=lookup+function

Works now :)

[C3vette75]

KP
In the lookup expression that Blacky supplied change it to this. Lookup({GM.ACPS},4.90,14.31,4.84,14.00,4.67,13.00, 4.50,12.00,4.33,11.00,4.16,10.00,3.99,9.00,3.82,8. 00,3.47,6.00,3.13,4.00,2.79,2.00,2.45,0.00,2.03,-2.46,1.61,-4.91,1.19,-7.37,0.77,-9.82,0.35,-12.28,0.02,-14.29)"
It looks like he just copied your numbers from your post but what you posted changes from psi to in. (Hg). In. (Hg) is negative pressure. I think you need to keep the same units. This will keep it all in psi.

[kp]

I did the negative thing but it still didnt work, have to start with the lowest voltage first before it works.

this is what I have now, I split some of the voltages to read a little finer:

"Lookup({GM.ACPS},0.02,-29.10,0.35,-25.00,0.77,-20.00,1.19,-15.00,1.61,-10.00,2.03,-5.00,2.45,0.00,2.62,1.00,2.79,2.00,2.96,3.00,3.13, 4.00,3.30,5.00,3.47,6.00,3.64,7.00,3.82,8.00,3.91, 8.50,3.99,9.00,4.08,9.50,4.16,10.00,4.25,10.50,4.3 3,11.00,4.42,11.50,4.50,12.00,4.59,12.50,4.67,13.0 0,4.76,13.50,4.84,14.00,4.90,14.31)"

I dont know how accurate it is, I'm really just looking for run to run variation. Havent driven the car but it reads '-psi' at idle and drops to zero when Ithe boost gauge hits zero so close enough. I'll get it into boost and see where its at.

[joecar]

...,0.02,-29.1,0.35,-25.00,0.77,-20.00,1.19,-15.00,1.61,-10.00,2.03,-5.00,...

kp, you're mixing units (psi, inHg); use the psi values that C3vette75 posted in your ascending order list.

[joecar]

kp, your pressure range (-15psi to 15psi) scale is guage pressure (referenced to BARO) rather than absolute pressure;

suggestion/observation: it is easier to discuss and compare data in the same range scale that the PCM uses: absolute pressure;
for 2 bar, the range is 0psi to 30psi (or 0kPa to 200kPa), so just add the BARO psi value to all your psi values in the lookup list.

[kp]

It doesnt really matter, I realize psi and inhg are two different things. I just have the graph displaying 0-15psi anyhow. The negative numbers still show but not on the chart. I could just get rid of anything under 2.45v actually and it wouldnt really matter - its just for comparing boost numbers run to run.

Works great though, this is just 5psi with the car in high gear gainst the converter at 4500rpm and the boost gauge read 5psi as well - close enough for me. Too hat to blasting around the streets but I'll see how close it reads to gauge next time at the track..

[Blacky]

Been trying to make it work for almost 3 hours - decided to do a search and found this:

http://www.efilive.com/forum/viewtopic.php?t=1717&highlight=lookup+function

Works now :)

:oops: Sorry about that, I did just copy your numbers and forgot about the ascending requirement.

I have also implemented interpolation which makes the "in between" values more accurate.
That will be available in the next release.

Regards
Paul

[kp]

Been trying to make it work for almost 3 hours - decided to do a search and found this:

http://www.efilive.com/forum/viewtopic.php?t=1717&highlight=lookup+function

Works now :)

:oops: Sorry about that, I did just copy your numbers and forgot about the ascending requirement.

I have also implemented interpolation which makes the "in between" values more accurate.
That will be available in the next release.

Regards
Paul

No problem Paul, search can be your friend sometimes :) I tested it today with a vacuum pump and its pretty close to the boost gauge without any correction so it worked out well.

interpolation will be great - thanks again.