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How To Make An Oxygen Sensor For Your Kiln.


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#1 joshur

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Posted 03 December 2013 - 01:43 PM

Is there any interest here on how to make and use oxygen sensor for a  gas kiln, using an automotive oxygen sensor? or has this been done already? I built one a year or so ago and after working out the kinks, have had good results, If there is enough interest I will share what I have done and learned.

 Josh



#2 neilestrick

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Posted 03 December 2013 - 02:04 PM

Put your head in the kiln. If you don't pass out, there is plenty of oxygen. :D  But seriously, yes, let's hear your results!


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#3 Brian Reed

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Posted 03 December 2013 - 03:21 PM

Joshur,

  I am so very interested.  I fire gas reduction and would like to purchase an O2 reading device, but the cost is too high for me.  If you had an alternative that I could make I would so be all over that.


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#4 PeterH

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Posted 03 December 2013 - 03:50 PM

Hi,

There was another thread on this topic very recently called Kiln Flue Gas Analysis.

It included a reference to http://members.optus...ust_sniffer.pdf - but you should probably

read the entire thread.

Regards, Peter



#5 joshur

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Posted 04 December 2013 - 12:44 PM

To start with I will show a  a picture of the basic parts of the setup and discribe their use and function. The parts are, a digital multi meter, $2.99 on sale at harbor freight, new automotive oxygen sensor, $25, about $10 in plumbing parts, and a long enough piece of 5/8 od ceramic tube to go through the wall of your kiln,$15.

 The adaptor from the ceramic tube to the iron tee is a 5/8" compression fitting to pipe.

 The function, and results of the store bought $1200. O2 sensor and this home made one are essentially the same, I started using the fancy one and was able to study and test it against the home made one, to compare the components, data and results.

The store bought one, samples the air directly in the kiln, while  the home made one has to siphon the gas out though the ceramic tube to the sensor. Both kinds of sensors use the same basic kind of system and both give their readings in DC volts, so all you are reading is an increase in voltage  as the O2 level decreases at certain tempratures.

 

 I am a slow at typing and need to get some work done, and will break this up into several parts, so this is all for now.

 

 Josh

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#6 jrgpots

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Posted 04 December 2013 - 01:12 PM

I am converting an old electric to gas kiln. I'm interested and look forward to your next post. It looks like you use the long galvanized pipe as a small chimney that draws chamber gas past the sensor?..... great idea!

Jed

#7 joshur

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Posted 04 December 2013 - 10:11 PM

The tricky part.

 

Is to get a consistent flow of kiln gas to the sensor and at the proper temprature. As different kiln designs have very different air flow and internal pressure, the sensor assembly must be set up to the individual kiln.

  A down draft kiln that has enough back pressure/ positive pressure is the easiest to set up and operate, all you need to do is drill a hole in the kiln wall, about 3/4 of the way up the wall, twards the back of the kiln, and away from peep holes, you really do not need much flow by the sensor, but it must be consistent.

 The tougher one is the updraft kiln, the updraft is often operating in a negative pressure mode, not only that but the kiln air flowing past the ceramic tube on the inside of the kiln wants to pull air in through the tube from the outside of the kiln, like the venturi effect in a carburetor.

 I did two things to solve these problems on an updraft kiln, one was to create a gas catcher inside the kiln to assist in getting the flow in the right direction, the other is a long  metal chiminey, heated  by the exhaust from the kiln.

 The first two pictures are of the gas catcher,  just a piece of soft brick that is partly hollowed out,  then cemented and pinned over the intake end of the ceramic tube, to funnel the gas into the tube. The third picture is the sensor assembly on the kiln,  the next two are the kiln with the sensor and chiminey pipe attached, and the last is just the chiminey pipe, which is just a section of 3/4" metal electric conduit that slips onto the metal pipe that comes out of the tee. The last picture is of the complete setup. Feel free to ask questions, or ask for more pictures if things are not clear.

 

 Next: Operating the sensor.

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#8 jrgpots

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Posted 04 December 2013 - 11:47 PM

I'm converting an old electric to gas, making a downdraft. I think I will add a 3/4 to 1 inch coupling then extend the chimney with 1 inch conduit. It should draw very well.

What type of analysis is possible? Is the sensor an "all or nothing" current reading? Can it be titrated to the O2 level?

Jed

#9 joshur

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Posted 05 December 2013 - 02:13 AM

Jed,

 

 The readings from the sensor  seem to be quite sensitive and cover a  broad range,

 The attached chart shows what is going on with the readings you will see on the meter,  the 0.1 to 0.8 readings on the left of the chart are volts,  when the meter is set to read in the say 2 to 20 volt range, your reading in the reduction phase might look like 0.712 volts and drop down to 0.345 for a few seconds after opening a peep hole on an updraft that would draw in extra air. Even when the kiln is very stable the reading will bounce around 0.020 or 0.030 volts. These readings seem to be very similar using either the commercial kiln sensor or the automotive one, same with the meters, fancy or cheap have similar readings, in fact some of the commercial units just use a relabeled common multimeter, as a readout.

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#10 joshur

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Posted 06 December 2013 - 09:07 PM

Using the O2 sensor,

 

One of the major advantages of the store bought sensor, is that it needs little or no maintenance, on the other hand, our home made version, should be cleaned and inspected prior to each use, turned on at a specific point, and closed up immediately upon shutting down the kiln. 

The first step to setting up the kiln to fire, is to clean the sensor and the intake pipe and chimney.  Picture one shows the sensor in the storage mode, pic two shows the sensor after a firing, and three  is  the cleaning of the intake tube, it is best to clean the sensor and tube first as some debris, soot, spiders, etc.  may be blown into the kiln, I use compressed air to clean the sensor, and tubes. The threads on the sensor are slightly smaller than the thread of the 1/2" iron pipe, so a couple wraps of aluminum foil on the sensor threads, takes care of this and makes the sensor easy to unscrew for cleaning, you could find a proper adapter, but the foil works fine for me.

 The sensor exhaust  should be kept covered as pictured in #1 and the chimney not connected until the kiln is close to reaching the temperature for starting reduction, there are several reasons for this, one is both type of sensors, do not give accurate readings until  they reach a certain temperature, but most importantly our sensor operates at lower temperatures than a internal sensor and during the kiln temp rise from start until it is at least 1000F there is moisture, soot and other stuff being given off by the kiln and this can condense on the  sensor, and the temperature at the sensor may not be high enough to burn it clean.

 So, I clean the sensor, put it back in, close it up, clean and stack the kiln, then start the kiln. When the cone 011 guard cone for reduction starts to go down, I  remove the cover, see picture 1,  put on the chimney, pic 4, and hook up the meter, 5,  at this point the kiln is warm enough to provide hot dry air to the sensor, and quickly heat the chimney to establish a good kiln gas flow past the sensor, carefully check that the chimney near the sensor is getting warm or hot to confirm a good flow of gas. The portion of the chimney pipe that is in the kiln exhaust, may get hot enough to glow red.

 When you turn the meter on at this point, you should start to see a gradual rise in the voltage, and by the time the kiln is hot enough to need reduction, the sensor assembly should be giving an accurate reading.

This kiln is a little touchy on getting the gas air mix just right to get the reduction I want and sufficient temperature rise, but once set it requires little adjustment.

With a sensor to establish the proper carbon monoxide level, you may not see some of the usual indicators of reduction, especially as the kiln gets hotter, such as smoke, soot on the peep plugs, and a cloudy or slightly obscured view of the ware through the peep, as the kiln should be operating more efficiently while still maintaining the required carbon monoxide level.

 As soon as I shut off the kiln I disconnect the chimney and cover the sensor exhaust  to prevent outside air from going through the pipe into the kiln, for the usual reasons not to have an opening on the side of a hot kiln. 

 

 Next: Results

  ,

Attached Files

  • Attached File  O2-1.jpg   631.19KB   9 downloads
  • Attached File  O2-2.jpg   140.37KB   10 downloads
  • Attached File  O2-4.jpg   302.31KB   14 downloads
  • Attached File  O2-5.jpg   811.29KB   8 downloads
  • Attached File  O2-7.jpg   489.87KB   7 downloads


#11 joshur

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Posted 07 December 2013 - 11:47 PM

Results:

 

First, a picture of the kiln and sensor in operation, this is right at the end of the firing, giving the kiln a short heavy reduction soak prior to shutdown.

This kiln is probably 45 years old, it has an interior dimension of  37" x 37" x 42" and a stack area of 24" x 28" x 37" it uses about 30 gallons of propane for a cone 11 firing and takes 7 to 9 hours.

Next are a couple pictures of my work at my current show at the Mendocino Art Center,

 

Most all of these pieces were fired using this kiln and sensor and almost all this year.

 

 Josh

Attached Files

  • Attached File  O2-8.jpg   598.89KB   5 downloads
  • Attached File  20.jpg   250.48KB   7 downloads
  • Attached File  25.jpg   171.98KB   9 downloads


#12 jrgpots

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Posted 08 December 2013 - 01:54 AM

I am covinced...I'll do it.

Thank you for sharing. Your design is simple and functional. Great pieces.

Jed

#13 brickleypottery

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Posted 18 February 2014 - 08:17 PM

Thanks Josh!! You rock!!

 

Brian



#14 Ron&Jillian

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Posted 18 February 2014 - 10:54 PM

Very simple and great pictures that allow me to follow your design.  KUDOS and I think you should enter this in the homemade tools competition that Ceramics Daily does. Thanks!






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