Modifying O2 output

[J.W. Harris]

><CICIORA STEVEN JOSEP> wrote:
>
>>   I think I remember reading somewhere (this list?  the hotrod list?) 
>> that one way to get a little bit more liniarity out of an 02 sensor is to 
>> apply (something like) 0.6 v to it and measure the current into or out of 
>> it.  I also seem to remember seeing a circuit that will switch a load 
>
>>From a WWW page about O2 sensors, I got the following information:
>
>--> start of quotation <--
>
>     Almost always, the answer is no.  You must be careful to not
>     *apply* voltage to the sensor, but measuring it's output voltage
>     is not harmful.  As noted by other posters, a cheap voltmeter
>     will not be accurate, but will cause no damage.  This is *not*
>     true if you try to measure the resistance of the sensor.
>     Resistance measurements send voltage into a circuit and check the
>     amount returning.
>
>--> end of quotation <--
>
>So Steven's input confuses me a bit. May I apply voltage to an O2 sensor
>or not? Any inputs welcome.
>
>Jens
>
>
>

The o2 sensor amplifiers we use apply a bias of 450 millivolts to the sensor 
through a 1.2 meg resistor.  This voltage can be seen across the PCM input 
with a good digital voltmeter.  When the sensor is cold, and has a very high 
output impedance, this bias will cause the system to indicate a steady half 
scale voltage.  When the sensor warms up to about 600 F, it begins to 
function and this source is swamped out.  

To scale the o2 output you should build an op amp circuit with a couple of 
meg ohms of input impedance and I would guess about 100 - 200k of output 
impedance.  I don't know how your system functions with a cold sensor.

The control system should not "learn" out your adjustment to the system 
because it is made in the feedback portion of the loop.  As long as it still 
switches correctly everything should work fine.
----------------------------------------------------------------------------
J.W. Harris                                          Delco Electronics Corp.
Project Engineer                                     One Corporate Center
Powertrain Electronics                               M.S. CT40C
                                                     Kokomo, IN 46904-9005
jwharris at kocrsv01.delcoelect.com

Of course, all responses are my own and should not be mistaken for those of
Delco Electronics or General Motors.