Wide Ratio O2 meter

[Frank F Parker]

Guys,
For what its worth, here is my estimation of the problems necessary to
make a wide range meter using the Bosch and/or the NTK/Honda sensor.

The Bosch LSM-11 sensor:
 1. There are 3 curves at 650, 750 and 900 C from which we can ESTIMATE
    the transfer function to air fuel.
 2. The sensor temp may be deduced from from the internal resistance of
    the sensor which varies as follows:
			650 deg C	120 ohms
			750 deg C	 35 ohms
			900 deg C	 10 ohms
 3. Here is the major hangup. How do you measure the internal resistance
   of the sensor without disturbing its output. A 1979 SAE paper, 790143,
   shows a parallal resistance method in which a known resistance is put
   in parallal with sensor and change in resistance is noted. From that
   change, it is a simple formula to calculate the sensor internal
   resistance and thus its temperature.
 4. What is not so simple, at least for those of us with no micro
  design, is how you get a microprocessor to do this: you got to put
  resistor in parallal, measure resistance and do math- I guess on a
  rapid sampling basis so do not disturb sensor.
 5. Once you have the sensor temp, you can now go to your 2D map of
   air fuel vs temp of which we have 3 curves from above. Others have
   to be calculated from interpolation if temp is not at 650,750 or 900.
 6. All of the above has to be rapid enough to get at least 10 samples
   per sec data or you will miss rapid accels.
 7. The sensor is touchy. I have used alot in racecars and have overlayed
   many laps of data taken at 100 times per sec using a MOTEC, $3500,
  interface to the Bosch sensor with an analog out to datalogger. What
   you see is that it takes several laps for data to stabilize at the
  final a/f. It needs to be HOT. Thus you need a good heater controller
  design with supply at > 12 volts.
  8. When all of that is done, you really need to prove design on a dyno
  comparing it to a Motec, Bosch or other calibrated meter. I have both
  a Bailey meter which was calibrated on dyno against a Motec and a NTK
  sensor/interface which I offer as cal standards for someone's design.

NTK/Honda Sensor

  1. Jim is correct. The Honda sensor has 7 wires with cal resistor
   built in. That is good BUT it is not the problem. All it means is
  if you have an interface, the sensor can be replaced without a
  recalibration.
  2. The problem is the transfer function is VERY propioritory. No one
   I know knows how to drive and read the sensor. There is a SAE paper
  but it is pretty general. FelPro has a license so they build their
  own interface in their fuel injection ecm.
  3. Sooooo!! -without the data like we have with the Bosch, we don't
  know what to do.
  4. The NTK sensor is much faster responding than the Bosch and lights
  off faster too. It is the better sensor but untill some data shows
  up OR FelPro can get a license from NTK to manufacture a cheap a/f
  meter , don't see much hope for NTK. 
  5. Call up NTK and yell at them. They licensed a/f rights to Horiba
  which screws everyone with a $2500 price. It could be much cheaper if
  NTK would allow competition in the marketplace-sounds even illegal!

Hope above gives everyone the problems involved. Maybe someone good in
design can come up with something.

Flame suit on.

Regards,

Frank Parker
Motorsports Data Acquisition
fparker at umich.edu
313-429-2819