O2 Sensor current?

Ord Millar ord at aei.ca
Thu Mar 25 02:27:51 GMT 1999


This is the standard way of telling if the O2 is at temperature yet... many
systems will bias the sensor to .45 volts through a very high resistance (10
megaohms I believe).  Once the sensor is at temperature, it does provide
enough current to move the voltage away from the preset level.


-----Original Message-----
From: Wen Yen Chan <chanwe at ecf.utoronto.ca>
To: diy_efi at esl.eng.ohio-state.edu <diy_efi at esl.eng.ohio-state.edu>
Date: Wednesday, March 24, 1999 8:49 PM
Subject: Re: O2 Sensor current?


>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.
>>
>>
>>
>
>




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