Trying to learn about oxygen sensors

I like the idea of having an air/fuel ratio gage on my gasifier engine. It’s one thing to add one of those Sunpro gages to a vehicle that already had an oxygen sensor, but there’s apparently more to it if your engine doesn’t already have one. I have listened to a few guys who are working with them and I have watched a few videos and read some other forums, too.
So, I got started by buying the Sunpro gage and a narrow band sensor. Narrow band because I didn’t want spend a lot of money.
Anyway, I did see one youtube video of a guy heating up one of those sensors and measuring the output with a digital VOM. He noted that the readings jumped all over the place, so I thought I’d do a little experimenting on my own.
The result is this video, if you are interested:

Next, I will add the Sunpro gage into the circuit and work on a better way to inject more contollable propane. Then I will send the signal to my arduino datalogger.

Please let me know if I did anything wrong here.

Pete Stanaitis

Good Morning Mr. Pete ,

Enjoyed the video , thanks for posting.

Looking good Pete. One thing to bear in mind, and you’re discovering this: The O2 sensor is rarely at .45 volts. That’s a scientific “ideal” or target. It mostly flip flops between “Lean!” at 0 volts and “Rich!” at 1 volt. The computer does it’s best to keep the voltage flip flopping at a steady even rate, so that it crosses the ideal mark more times, and is “on average” at the right mixture. This can happen several times a second.

The Sunpro gauge is doing some smoothing and averaging for you. It takes the flip flop voltage and tries to average it out to get something of a steady mixture reading. Otherwise it would be completely unreadable.

A wideband sensor is different. Here you are adjusting the current to maintain a voltage, and measuring the current required. This happens with a special box, which translates it into 0-5 volts. The current varies much more smoothly and over a wider range. The wideband gauge is displaying pretty much a direct smooth voltage output from the controller, which is doing all the hard work. This is why they are much more expensive than the narrowband gauges, but more accurate especially at lean mixes.

Yes, yes. Chris Saenz your in-use non-lab O2 sensor explanations are spot on.
I’d like to expand this:
The narrow band is a signal producing OUTPUT sensor on this same catagory as pezio-crystal-electric knock and many early barometric and even magnetic pulse sensors. Weak signal outputs very subject to outside signal interfernce confusion.
The wide band sensor is in a Regulated power (voltage or current), or supplied frequency MODIFYING sensor grouping: all later air flow, speed, baro/manifold/evaporative pressure and even temperature sensors now. Takes a lot more electronics to supply the regulated sensor imputs and translate the sensors modified outputs to a into now a system digetal useable data pacs to feed into the controller system. Much more stable, much less interfered with data pac info then into the whole control system.

Auto O2 sensors ONLY measure the REMAINING oxegen (fron any source) in the engine exhaust stream. They measure NOTHING else. You must infer anything else. Every different HC fuel will have a different ideal in the engine cylinder air to fuel mix ratio range for the power and load demand.
450 millivolts on the narrow bands is idealized for gasoline fuels. Kinnda’ OK for for dense HC methane and propane fuels also. Unusable sensor for diesels useally having an an intended excess engine exhaust O2 pass through for the best ecomony and least soot.
Woodgas you seem to want to see a very “lean” O2 exhaust output signal. This would be a LOW narrow band millivoltage output at the sensors low end of range capabilty therefore inaccurate. Any sensor or gauge needs to be kept somewhere near the center of range for normal operation if you want resonable accurate info to control by.

PeteS spend the bucks for a wide band system if you intend to imput this into any electronic contoller to get a usable, reliable signal imput.
I’ve seen guys woodgasing using complete E-bay Bosch wide band kits for as low a \$129. USD

For good post reactor woodgas control I’d want to be looking at CO and CO2 percentages and balances live streamed as more valid and important control points.
Now a whole level or two up in price and contamination senstitvity to do this. Gasifier direct core hearth temps, outputed gasses all cist bucks to read reliably with durable sensoring. Yep what you will need for finite feed back automation control.

Put a human operator as the control loop it is easy, simple and cheap to system build then. KISS. I like that.

Regards
Steve Unruh

Thanks for this Pete. I will be watching a learning here with you. I haven’t had much time to tinker with our system yet. But its coming soon.