Lambda Sensors and Catalyst Temperature Measurement

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Re: Lambda Sensors and Catalyst Temperature Measurement

Post by Avdr » Sat Jan 26, 2013 11:04 pm

Earlier in the thread, when dealing with the LSU4 sensor. It was stated that in order to read resistance of the sensor, the sensor had to be either effectively disconnected from the ECU in so far as its abilty to be a lambda sensor is concerned. Or, using a high frequency wave measure the resistance by a drop in amplitude.

I don't think its going to be a simple as connecting up some channels to a few wires, while the ECU has power, and obtaining useful readings for calculating the resistance. The readings are going to be infulenced more by sensor activity than anything else.

Have you tried using an IR temp gun downstream/upstream of CAT on a known good car, and comparing to ECU/thermocouple value?

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Re: Lambda Sensors and Catalyst Temperature Measurement

Post by KimAndersen » Mon Jan 28, 2013 11:08 am

Hi Richard

I'm glad that i could be of some help here.

But to dig even deeper in this matter - have i found the patent from Robert Bosch there in detail explain how the lambda sensor works and how the temperature measurement are made.

First a warning - this document is heavy reading - but rewarding in the end.
(76.58 KiB) Downloaded 522 times
I have cross check the lookup table from Lamborghini regarding temperature versus resistance against the patent from Bosch - see Fig.2a for further details and they seems to match very well in the higher region of the temperature scale.

One thing to remember about lambda sensor and their internal resistance through the Nernst cell are - that the resistance are different from a LSU 4.2 to LSU 4.9 - so have this in your mind when you make your measurement.

As AVDR mentioned earlier - is there a possibility that measurement may be disturbed - but it´s to soon to tell yet.

I will be nice to hear the outcome of this experiment or test.

Happy reading with document from Bosch.


A small correction to the above.

The temperature/resistance scale scale shown the in patent from Bosch seems to be a LSU 4.9 lambda sensor where the lambda sensor for the Lamborghini look-up table is a LSU 4.2 - this could explain the difference in resistance in the nernst cell between the two diagrams.

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