Re: Ohm's law, O2 Sensor testing and Air/Fuel Meters - Saab 9000 Bulletin Board - Saabnet.com
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Re: Ohm's law, O2 Sensor testing and Air/Fuel Meters
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Posted by BobS (more from BobS) on Sun, 19 Oct 2003 19:03:37 Share Post by Email
In Reply to: Ohm's law, O2 Sensor testing and Air/Fuel Meters, TRJ, Sun, 19 Oct 2003 18:41:30
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#1 3 wire sensors use the body of the sensor for ground, common, or sensor return. If the heater wire were used the voltage offsets due to the heater current and resulting voltage drops in the circuit would affect the sensor signal,
#1a A multimeter certainly can affect the sensor reading, fortuately most modern multimeters have very high impedance specifically designed minimize their affect on measured circuits.
#2 Any circuit connected to the O2 sensor circuit should have a high impedance (resistance) Preferably a couple a couple orders of magnatude greater than the sensor. Note, the O2 sensors impedance is also quite high. Actually the O2 sensor is a battery that generates a voltage when there is a difference in oxygen levels between the internal and external electrodes. Generally something with an impedance > 1 meg ohm is best.
#3 My son built one many years ago and used it extensively on his 1985 SPG. A good tool when doing mods. I've found a multimeter with a graphical bar works quite well.

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