I thought I would post this.
It answers a lot of questions for those curious about narrow band O2 sensors. It's from the Innovate WB board.
"Using a narrowband O2 sensor to measure/tune AFR or Lambda is pretty much impossible. The only Lambda number that will be correct is 1.0.
The reason is as follows:
A typical NBO2 sensor puts out a voltage between 0.1 and about 1.1V. Around Lambda 1.0 (14.7 AFR for gasoline) the voltage jumps from low voltage to a higher voltage as the mixture gets richer. At Lambda 1.0 the output is 0.45V typically. The curve at that point is very steep. Below Lambda 1.0 (richer) the voltage rises slowly the richer the mixture is.
BUT:
Although the slope of the sensor output curve at that rich region is fairly constant, the voltage offset is not. Depending on sensor temperature, an AFR of 12 can be 0.7V or 1.1V or anything in between. This means that even though you could make a millivolt table measuring AFR/Lambda vs. output of a NBO2 sensor (and program that into a meter), this table will be only correct for one particular sensor temp. for each of the measured points.
For example:
865mV on the NBO2 sensor can mean anything between an AFR of ~10 (high sensor temp) to an AFR of ~14 (low sensor temp).
If the sensor temperature is not precisely controlled (and it is not, typically), the millivolt outputs of the O2 sensor can tell you only rich, stoich, lean. Basically saying that the output is above, at or below 0.45V. And that is what it is designed to do ONLY.
Measuring AFR with a NBO2 sensor is like trying to measure battery voltage with a relay. If it clicks, voltage is there, but it's impossible to tell if it is 7V or 18V.
A lot of people believe there is a 'magic' mV number to tune while using a NBO2 sensor. This mV number is of course useless for the above reasons. It can change (by several hundred mV) even depending on the state of your battery and charging system (more or less heater voltage for the NBO2 sensor).
Regards,
Klaus"
Paul
It answers a lot of questions for those curious about narrow band O2 sensors. It's from the Innovate WB board.
"Using a narrowband O2 sensor to measure/tune AFR or Lambda is pretty much impossible. The only Lambda number that will be correct is 1.0.
The reason is as follows:
A typical NBO2 sensor puts out a voltage between 0.1 and about 1.1V. Around Lambda 1.0 (14.7 AFR for gasoline) the voltage jumps from low voltage to a higher voltage as the mixture gets richer. At Lambda 1.0 the output is 0.45V typically. The curve at that point is very steep. Below Lambda 1.0 (richer) the voltage rises slowly the richer the mixture is.
BUT:
Although the slope of the sensor output curve at that rich region is fairly constant, the voltage offset is not. Depending on sensor temperature, an AFR of 12 can be 0.7V or 1.1V or anything in between. This means that even though you could make a millivolt table measuring AFR/Lambda vs. output of a NBO2 sensor (and program that into a meter), this table will be only correct for one particular sensor temp. for each of the measured points.
For example:
865mV on the NBO2 sensor can mean anything between an AFR of ~10 (high sensor temp) to an AFR of ~14 (low sensor temp).
If the sensor temperature is not precisely controlled (and it is not, typically), the millivolt outputs of the O2 sensor can tell you only rich, stoich, lean. Basically saying that the output is above, at or below 0.45V. And that is what it is designed to do ONLY.
Measuring AFR with a NBO2 sensor is like trying to measure battery voltage with a relay. If it clicks, voltage is there, but it's impossible to tell if it is 7V or 18V.
A lot of people believe there is a 'magic' mV number to tune while using a NBO2 sensor. This mV number is of course useless for the above reasons. It can change (by several hundred mV) even depending on the state of your battery and charging system (more or less heater voltage for the NBO2 sensor).
Regards,
Klaus"
Paul
