O2 Sensor current?

[rr]

Ah yes, the ECM bias's the O2 sensor to 450mV, then looks to see
when it starts to change from that value. When it does, the
sensor is coming alive, up to temp.

You should be able to get around this by putting a large value
resister in series with the op-amp output. Maybe a 1 or 2 Meg Ohm.
This will then simulate the output impedence of the O2 sensor.

BobR.


Wen Yen Chan wrote:
> 
> Hello,
> 
> A while back I tried to offset the reading from my O2 sensor with a simple
> op-amp circuit. The circuit worked fine but the ECU always thought the
> sensor was hot (even after a cold restart). It seems that the Honda ECU I
> was playing with pulled a small current from the sensor to check if it was
> lit. When my circuit was added the ECU saw the low output impedence of the
> op-amp and just assumed the sensor was hot.
> 
> Wen
> 
> On Wed, 24 Mar 1999 Teller.John at orbital.com wrote:
> 
> > O2 Sensors do not draw current (excepting the heater in a heated 02
> > sensor), they are in fact a voltage source.  Not only that, they are a high
> > impedance voltage source and therefore do not put out much current at all.
> > The voltage drop through a 10K resistor is going to be negligible due to
> > the miniscule currents (less than a microAmp) involved.  To figure the
> > voltage drop accross your 10K resistor, use Ohm's law (E=I*R) where I =
> > 0.0000002 Amps and R = 10000 Ohms for a voltage drop of 0.02 Volts.
> >
> > If you want to change the output voltage of one of these devices, you
> > probably would be better off using an op amp circuit with a gain factor
> > less than 1.  Any loading of the output of these devices will at best
> > provide erroneous readings and at worst destroy the sensor.  See the
> > Forrest M. Mims books which are (or at least used to be) available from
> > Radio Shock for some examples of these circuits.
> >
> >
> >