Open Air readings

[elmo0104]

Hi

I'm new here. I've made my own shield based on bylund information. It works but have some question- in open air a have a 20% content of oxygen. Most of resistors from schematic was 0.1% of precysion (not sure how to explain this value. I hope U anderstand).
Is this normal? I have bosch sensor but not new- can this be a problem?

[Christian_Bylund]

Hi elmo0104,

If you are reading around 20% in air you are close enough for any automotive readings. What calibration value are you reading, when the CJ125 is in calibration mode?

The reading of the sensor is depending on many factors, temperature of the cell, supply voltage of the CJ125, ADC voltage reference, ground plane interference, EMC, tolerances in components, the list goes long once you start to think about it. Our schematic describes an education approach on how to use the CJ125 controller for the Arduino.

I should also point out that the oxygen level calculation described by Bosch and used in our code is very much simplified. Our code is now designed to use a lookup table for the lambda, which is very accurate from a software conversion point of view. So to summarise, very good for measuring exhaust gases. Less accurate in measuring very lean gases such as air.

I hope this answers your question.

[elmo0104]

Thank you!

The calibration readings are 176-177. Fiew firsts readings of o2 content after device reset are 20,58 ; 20,20 ; 20,00; 19,60 ; 19,80. and then is oscilating around 20%. My goal is to measure O2 content 1-5% . Will it be acurate enough for this range of o2 content?

I have another question about your app for display lambda and o2 content. It was working when I was using the "Lambda App" arduino software. Then when I load the code from GitHub to arduino it is not working byt now I can read o2 content from adruino IDE. Is it normal? What kind of data should be sent to PC by USB to use your PC "Lambda app"?

Regards
Peter

EDIT:

https://photos.app.goo.gl/VDGjrm9tUqvxEev36

It is the oil burner

[elmo0104]

I have tryed fiew different condition lambda sensors and the calibration values are the same on each . I have got:

UA_Optimal : 305
UR_Optimal : 177


Each sensor shows different O2 content at air and at exhaust pipe in my oil burner. I'm operating at 3-4% O2 content. Is it normal ? I have bought brand new sensor and will give it a try when arrive.

[Christian_Bylund]

Hello Peter, sorry for my late reply.

What kind of data should be sent to PC by USB to use your PC "Lambda app"?

The GitHub code is not compatible with the PC application. Either a front end is used, or text output is used. However the GUI code requires an update to improve accuracy, this is already implemented in the GitHub code.

UA_Optimal : 305

So in calibration mode the CJ125 outputs 0% oxygen (λ=1), in your case of 305 it means 0.99λ.

The LSU 4.9 sensors are calibrated in factory by laser which is then read by the CJ125 controller. However they need to operate at the right temperature, set by UR_Optimal during calibration. Sensor accuracy will drift due to ageing.

I suggest you use the GitHub code and use Lambda instead of oxygen, it is converted very accurately. 3% Oxygen = λ 1.18.

[Christian_Bylund]

https://photos.app.goo.gl/VDGjrm9tUqvxEev36
It is the oil burner

Hello Piotr,

Are you using the lambda feedback to optimize the burner? - For example a fan control.

[blacksheepinc]

Hello Christian,

Actually I have something similar problem.
After heating phase(sensor gets hot also), it stops with error message 0xE8FF.
Also, if I modify the code it turned out, the the calibrations values are "normal" Ur=173, Ua=303, however when it exists from calibration mode, Ur is around 55-56. And does not change, it is stucked.
I have a genuine Bosch sensor.

BR
Mark

[Christian_Bylund]

Hello Mark,

It would help to know if this is one of our genuine shields or if you have made it yourself?

After heating phase(sensor gets hot also), it stops with error message 0xE8FF.

0xE8FF indicates an SPI issue or reset in transmission issue. The CJ125 diagnostics register should always respond with 0x28 followed by the fault code in bits. So 0x28FF means OK, probably what it was trying to say.

Also, if I modify the code it turned out, the the calibrations values are "normal" Ur=173, Ua=303, however when it exists from calibration mode, Ur is around 55-56. And does not change, it is stucked.

So the way the UR value works is that the higher it is the colder the sensor is, your sensor is indicating overheating. How is your regulation?

I have a genuine Bosch sensor.

Good!

[blacksheepinc]

Thanks for reply!
Made it after your schematic, and used your code.
After using a new bosch IC, the SPI issue is disappeared.
But still, with stone cold sensor UR is around 55, while calibration value show 157. So the analog reading is fine.
I have a brand new sensor, but I guess it is faulty somehow.

Hello Mark,

It would help to know if this is one of our genuine shields or if you have made it yourself?

After heating phase(sensor gets hot also), it stops with error message 0xE8FF.

0xE8FF indicates an SPI issue or reset in transmission issue. The CJ125 diagnostics register should always respond with 0x28 followed by the fault code in bits. So 0x28FF means OK, probably what it was trying to say.

Also, if I modify the code it turned out, the the calibrations values are "normal" Ur=173, Ua=303, however when it exists from calibration mode, Ur is around 55-56. And does not change, it is stucked.

So the way the UR value works is that the higher it is the colder the sensor is, your sensor is indicating overheating. How is your regulation?

I have a genuine Bosch sensor.

Good!

[Christian_Bylund]

But still, with stone cold sensor UR is around 55, while calibration value show 157. So the analog reading is fine.

Hello Mark,

Sorry for my late reply. What I did was to hook up the Lambda Shield without the heating enabled. So with sensor cold, UR reads approximately 870 bits (4.25V). I hope it helps you in your troubleshooting. I would off course be happy to sell you a Lambda Shield as a reference for your own circuits.