O2 sensor output vs temp vs impedance

Fred Miranda fcmtb at ix.netcom.com
Wed Jul 9 03:38:09 GMT 1997


You're right Frank, the info I have is on the National LM9040.
They call it a dual lambda interface. 
Got it from their web site.

Also Frank, any way you could put a copy of that graph on the DIY web site
so all of us could get a look at it. 
I have a copy but it's a crappy gif of a fax.

Fred

At 10:31 PM 7/8/97 -0400, you wrote:

>Would be interested in that IC chip #. I know that NAtional makes some
>o2 sensor interface chips.
>
>The answer on whether to control sensor temp for accurate a/f measurements
>is an emphatic YES- you must do that. I have a enginering graph from
>Bosch for their LSM-11 sensor which is specially made for rich field a/f
>measurements. It is their Motorsports sensor. It does , however, have
>about the same output curve as a std production O2 sensor. This graph
>shows internal resistance of sensor changes  as follows:
> 	SENSOR INTERNAL RESISTANCE       	TEMP
>
>		10 ohms				900 deg C
>		35 ohms				750 deg C
>		120 ohms			650 deg C
>
>This results in the following change in a/f for a particular output
>voltage, say 0.78 volts.
>
>		VOLT		A/F		TEMP
>
>		0.78		13.23		900 deg C
>		0.78		14.11		750 deg C
>		0.78		14.41		650 deg C
>
>Thus you can see that there is over a 1 a/f # change if you do not
>control the temp. Bosch does in their high $ LA-2 meter and so does
>Bob Bailey in his $1000 O2 meter that uses the LSM-11. I have one of these
>and have had it checked on a dyno against both a MOTEC a/f meter( $5000)
>and the measured air and fuel flows. It was very close to the measured
>values. $1000 is not cheap, but way less than any other ACCURATE meter
>and mandatory if you are to do any serious tuning with a DFI or major
>mods of a production efi.
>
>Hope this helps.
>
>Frank Parker
>fparker at umich.edu
>
>PS: Very good book on automotive sensors (including O2) is "Automotive
>Electronics Handbook" by Jurgen, ISBN:0-07-033189-8
>
>fp
>
>
>
>




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