O2 Sensor type?

Mark Boxsell mrb at mail.mpx.com.au
Wed Jan 17 08:24:29 GMT 1996


>
>FWIW, I have recently bought an NGK UEGO and have the prices sitting in
>front of me.  Sensor AUD$950, loom $120 and controller $750 ex tax.  They're
>not cheap!
>
>I ran some calibration runs last week against an ADS9000 four gas analyser.
>There is some problem with the UEGO in that the voltage output wrt AFR
>has a 1.7V discrepency at stoiciometric and about 1.0V at the extremes
>of my tests (12:1 and 25:1).  I'll be faxing NGK later today to find out 
>why the output is out of spec.
>
>Robert Dingli
>-- 
>----------------------------------------------------------------------
>             Robert Dingli           r.dingli at ee.mu.oz.au
>
>Power and Control Systems                 Thermodynamics Research Lab
>Electrical Engineering                    Mechanical Engineering
>   (+613) 9344 7966                          (+613) 9344 6728
>  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
>----------------------------------------------------------------------
>
>
Robert,
        Are yes, but is your ADS9000 correct! Four gas analysers use a
"chemical cell" O2 sensor and they have a life of only about 12-18 months.
Oxygen is used along with the other gases(3) to calculate the AFR so if this
sensor is not reading correctly your AFR will be all over the place. The
other problem is that most "cal gas bottles" do not contain any oxygen so it
is hard to check.
With the "firewall mounted" controller NTK only claim +/- 0.5 AFR as far as
I can remember.
I would be very suspicious of it being 1.7 volts out at stoiciometric that
does not sound correct to me. After all it only gives a 0-5 volt output so
an error of 1.7 volts is pretty bad!!!!
Make sure you have enough power for the heater circuit I have run into
problems with cicarette lighter plugs ie. dirty contacts, etc.
The early controllers could drive a meter movement directly however the
later type which you have cannot, so make sure you are not "loading" the
output. High impedence input or build yourself a voltage follower op-amp to
give it some grunt!
Also it is very sensitive you can watch each cylinder's gases coming down
the exhaust pipe if you hang a scope off it!
Also do you have the correct output table ie. volts to AFR. Also 25:1 is a
bit on the lean side of things to be testing spans. Quoted scale shows 10:1
- 22:1 so 25:1 is really pushing it.
14.7:1 AFR = 3 volts.
10:1   AFR = 1.7 V
22:1   AFR = 2.65 V

  Hope this helps,
                    Mark Boxsell
                    MRB Design
                    Sydney Australia
                    Fax (02)629 4796 (International 61 2 629 4796)




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