How to create a custom probe for a rail pressure sensor.

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KimAndersen
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How to create a custom probe for a rail pressure sensor.

Post by KimAndersen »

My first thought was to show how to create a custom probe for a rail pressure sensor which is used in many 1.6 and 2.0 TDI across the V.A.G. platform.

To begin with I would say - it easy to make a custom probe if you have the right specifications / datasheet over this common rail pressure sensor which I thought I had, but it didn't take me long figur out the output voltage from the rail pressure sensor were out of scaleling in terms to wrong pressure values from the VCDS software, but it´s another story.

This common rail pressure sensor is mounted in a Skoda Octavia 1.6 TDI (77kW) engine type (CLHA) 2014 and there is absolutely nothing wrong with this car or the pressure sensor for that matter as well.

Where to start, when there is documentaion on this pressure sensor or at least very limited info. In terms of a known manufactur - I´ll say Delphi based on the shape of the sensor foot. Its not a Bosch pressure sensor for sure.

The info on the sensor says ( 04L 906 054 ) TN3 A1 RPS22 MALAYSIA - so this sensor could be from a manufactur called SENSATA in malaysia, but I really dont know.

RPS22 on the sensor equals to the maximum operating pressure of 2200 bar that this sensor can handle which is vital to know when you make a custom probe, so thumbs up for that.

So this commonrail pressure sensor has a range of 0 to 2200 bar which I has to find the corresponding output voltage this sensor produce. The most sensors have a voltage output from 0.5 to 4.6 volt and with a linear curve.

The next step will be to find the resistance (OHM) of the pull-up resistor which is inside the ECU. Disconnect the sensor plug and measure the resistance between PIN (3) and PIN (2) of the 3 PIN connector and the outcome that I got was, 4920 OHM which will be used later to determind the final output voltage from the sensor.
SKODA OCTAVIA 1.6 TDI 77KW WIRING COMMONRAIL PRESSURE SENSOR
SKODA OCTAVIA 1.6 TDI 77KW WIRING COMMONRAIL PRESSURE SENSOR
If you think of the commonrail sensor as a voltage diveder its easyer to understand.
With the help of OMHS law and the basic understanding of a voltage diveter can you calculate the right resistor that correspond a specific voltage from this sensor.

The easy way to create the correct scaleing curve is to use 50 Kohm potentiometer which covers the scale from 0 to 2200 bar. Place the potentiometer leads between the PIN2 ( Signal ) and PIN1 ( Ground ) on the 3 PIN connector which goes to the ECU.

The next thing you has to use in order to get the pressure reading correct is a OBD II /EOBD scanner tool or in my case - I used the VCDS software which a exelent tool for VAG cars.

One last thing before you are ready to turn potentiometer and at the same time watch the pressure readings from the VCDS software is to connect a DMM to PIN1 and PIN2 - you are now ready to take notes of the output voltage and the pressure (Bar).

How many data point did I make !!!.

I made 2200 data points as the scale goes to 2200 bar, so from 0 bar of pressure to 2200 bar does I´ve a voltage reading.

No - I didnt.

I created 3 data points and the rest did the CurveExpert software do in terms of generating a linear curve which I later can export to Picoscope software.

Here is the linear curve that that the CurveExpert software did generate from my data points.
RAIL PRESSURE SENSOR 04L 906 054 CURVE
RAIL PRESSURE SENSOR 04L 906 054 CURVE
As I said in the beginning it´s difficult to create a custom probe when you are missing some information or specifications and this the reason that I did those extra steps to be sure that I got the right resistor value and finally confirmed this with the VCDS software.

If you got the correct specification over the sensor then simply plot the value into the Picoscope software under the menu button called "EDIT THE LOOKUP TABLE" or import the data file you have created as I did.

I´ve uploaded this psdata file where it shows the three phases ( start-up - raise the from idle speed to 2000 RPM and finally engine shut off.
Skoda_Octavia_1.6TDI_77KW_CLHA_2014.psdata
SKODA TDI 1.6 TDI COMMONRAIL PRESSURE SENSOR
(1.61 MiB) Downloaded 394 times
CUSTOM_RAIL PRESSURE SENSOR 04L 906 054.psprobe
CUSTOM PROBE RAIL PRESSURE SENSOR 04L906054
(15.28 KiB) Downloaded 388 times
Here at the end I want to hear you guys what do you think about measure the rail pressure instead of a plain voltage output - does it have any diagnostic value to convert the voltage output from the pressure sensor to pressure scale in bar !!!.

Regards
Kim
Last edited by KimAndersen on Sat May 26, 2018 6:59 pm, edited 1 time in total.

ben.martins
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Re: How to create a custom probe for a rail pressure sensor.

Post by ben.martins »

Hi Kim,

Once again thank you for this invaluable work you have carried out and no doubt the custom probe you have created will be downloaded many times.

I guess there is value in knowing what the pressure is as this is normally what the scan tool will deliver on the screen. If you measured directly at the sensor and read off from the scan tool you'll quickly see if there is any discrepancies between the two.

Thank you once again for sharing your knowledge and please keep up the good work.

Kind regards

Ben

DNAutotech
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Re: How to create a custom probe for a rail pressure sensor.

Post by DNAutotech »

Hi Kim

Great job👍

Just a question: How do you connect to the scope?
Do you use a 5 volt power supply to the sensor?
Maybe you have a picture of your setup?

Regards Dan

KimAndersen
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Joined: Fri Nov 30, 2012 2:53 pm
Location: Denmark

Re: How to create a custom probe for a rail pressure sensor.

Post by KimAndersen »

Hi.

It's really simple to connect to this sensor.

Connect the red test lead to the signal wire (PIN 2) and the black test lead to ground of the sensor which is (PIN 1) as shown on the above picture.

Sorry - I don´t have any picture of this setup.

I hope this explanation was of some help to you. :wink:

Regards
Kim

victor2k
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Re: How to create a custom probe for a rail pressure sensor.

Post by victor2k »

Hello,
How can be used your method for some non-linear sensors like exhaust temperature sensor,air/fuel ratio sensor?
From my experience with the exhaust temperature sensor the best fit was at 5th order in Curveexpert but can we use this 5th degree in "table lookup" ?What math is used behind this function,what polynomial degree is used by Pico?Maybe a "residuals" function in custom probe can help us ...(this is a request for developers,of course). :D
Thank you
Attachments
exhaust temperature sensor.PNG

KimAndersen
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Posts: 230
Joined: Fri Nov 30, 2012 2:53 pm
Location: Denmark

Re: How to create a custom probe for a rail pressure sensor.

Post by KimAndersen »

Hi victor2k

The only way to use my method is when you have the correct temperature / resistance specification of that particular exhaust temperature sensor you are using.

If you have this it's possible to create a lookup table that you later can export to the picoscope. It seems that you already have created curve by using the Curveexpert software - so if the 5th degree curve is the best fit- then why not import that file to picoscope. BTW - I dont see any voltage versus temperature on your picture !!!

I do not think it's a good idea to apply this method to an air / fuel ratio sensor - because I do not think it would work, but on an exhaust gas temperature sensor, it works fine.

Some time ago, I made a small case study on the exhaust temperature (G235) of a Volkswagen Jetta TDI 2.0 - so I think you should start there if you plan to make similar project. I know the casestudy got a bit messy, because of my self.

Here is the link topic10217-20.html to the Volkswagen Jetta TDI 2.0 casestudy, which starts half way in the topic. BTW this casestudy is called "How to measure a Bosch LSU 4.9 wideband lambda sensor" just to make some confusion. :wink:


Regards
Kim

victor2k
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Re: How to create a custom probe for a rail pressure sensor.

Post by victor2k »

Hello and thank you for the answer,
The easy way is to put in the lookup table the measured values but...today I re-readed your first post related to the "linear curve" and a small devil started in my mind ...what math(I don't know why the math is cool :D ) is used by Pico,how accurate is the used polynomial approximation?
I found some infos in my backups related to the Denso sensors and inspired by your post(some .psprobe was created using lookup table and uploaded on forum),but how accurate it is? :o
I will use Curveexpert to find the perfect match and import the created math in Pico until the developers will agree the file format .dat :lol:
A final check is good to verify if your math serve to you or...not(for example please look how far is the 3th degree polynomial approx.)
3th degree.PNG
Sorry for hiding y values with "residual" report,also x bar,I use it in every approx. to see how good is the used math :wink:
5th degree.PNG
Best regards

KimAndersen
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Joined: Fri Nov 30, 2012 2:53 pm
Location: Denmark

Re: How to create a custom probe for a rail pressure sensor.

Post by KimAndersen »

Hi

BTW what version of Curveexpert are you using ?. The picture of the residual report looks a bit different than my version - I'm using Curveexpert Pro version.

Your data values from your latest plot are they taken from a datasheet or are they actual values that have plotted into your graph and by that I mean real voltage reading at the sensor ?

Regards
KIm

victor2k
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Re: How to create a custom probe for a rail pressure sensor.

Post by victor2k »

Hello,
I used 1.4 Curveexpert free version and data was collected using your easy way(20 kohm multiturn potentiometer as a voltage source monitored by pico 4425 and KTS with ESI for data reading from ECU).
Today I used a math but not work,can't see anything in Pico. :cry:
Thank you
Attachments
denso exhaust temperature.rar
(9.93 KiB) Downloaded 167 times
Denso exhaust temperature sensor.psmaths
(506 Bytes) Downloaded 214 times

KimAndersen
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Posts: 230
Joined: Fri Nov 30, 2012 2:53 pm
Location: Denmark

Re: How to create a custom probe for a rail pressure sensor.

Post by KimAndersen »

Hi victor2k

I have read some of your previous posts, and I can miss or overlook this question.
victor2k wrote:
Sat Nov 10, 2018 5:43 am
From my experience with the exhaust temperature sensor the best fit was at 5th order in Curveexpert but can we use this 5th degree in "table lookup" ?
Of Course, this can be used in the picoscope lookup table ? I dont understand this.

Do you have trouble with with lookup table in picoscope or is it accuracy of the generated curve from Curveexpert that you are concerning about.

One vital thing to remember when have created a curve in the Curveexpert software is to rotate the columens X1 and Y alias voltage/temperature before you save this file which you later on import to the lookup table in picoscope. If you dont do this it wouldnt work in picoscope as you cant rotate the columens in the lookup table.

The exhaust gas temperaure sensor you are testing is manufactured by Denso - do you have info regarding part number or perhaps some infomation of what car this sensor mounted in. I´ve lots of specifications on EGT sensor of the type RTD, but this Denso sensor is a NTC type - so its a another story.

It would be nice if I could see your Psprobe file over this EGT denso, just check that there is any obvious error with this file.

I could try to generate a curve if got the right specfications - I know I´ve your CurveExpert data file, but I´m missing the psprobe file. :wink:

Regards
Kim

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