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Diz

Oxygen Sensor/probe - Commercial Vs Homemade Auto Sensor

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As I consider how I am going to 'improve my pottery' this year, I consider purchasing an oxygen sensor, however the price is a BIG consideration.  I fire an Olympic torchbearer, an updraft kiln, using LP to cone 10.  For the past 6 years I have used a sensor made from a Bosch auto sensor (Roger Graham directions).  It has allowed me to get reduction in my kiln but it is spotty and I feel I have little or no control over it.  I realize that weather conditions play a huge part in a successful firing and I am wondering if the cost of the new sensor will be justified thru better LP usage, more even reduction and more control over my (reduction) firings. Pottery is more than a hobby, but not a full time job, yet I do a couple shows a year and my pieces sell in a couple local stores - I see the payback as spread over a couple years. 

 

Input from those with knowledge and experience with oxy sensors will be appreciated.  I find only 2 on the market and cost ranges from $800-1200 so please give your best suggestions.

 

Thanks!

Diz

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I have two of these oxyprobes. Both from axner-they are the 12 inch wall types One on a 35 cubic car kiln

the other on my 12 cubic updraft

The trouble you will have is in such a small kiln there is a lot of turbulence. This affects readings as it blows by unevenly. So where you place it will matter a great deal.

I do not think I would bother cost wise on that kiln to meter it. Its true meters are just another tool but this one will not pay for itself on that kiln. Spotty reduction is just the nature of that kiln (I call them trash cans as they are round and small and always fire unevenly)

The up side of these meters for me is non ceramic filks can keep kilns in reduction (like my wife) so I can be away during part of fire.

The downside of you current meter is its in the stack(exit flue of flame) as it cannot stand internal temps.

I would think you will see zero savings on propane use and you will have zero gain in reduction. This kiln is to small and dependent on stacking forms/shelve placement to matter with a meter.

You should by now be able to get kiln into reduction by viewing the hole in lid and a lower spy port-I call this seat of your pants firing and it works fine-I have decades of experience with it with consistent results . If you want better results spend your money on a different kiln-I know this is not what you are asking about but its the reality.

I would shop crags list for another kiln with that $800 seed money.

Mark

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Thanks for the info guys...

 

First I would LOVE to get another kiln but again the cost holds me back - never considered Craigs list for such a large purchase.  Will start looking...

 

With an oxyprobe I was hoping that it would allow me to 'fine tune' my damper settings, that it's R readings would be truer since they were internally taken. Currently with my auto oxy, I have it placed in the center of a wall between flame ports and about 2/3 of the way up the side. I do have the sensor sitting above the top port so it sits in the flicking flames in a mix of exhaust and fresh air so my readings fluctuate wildly.  I rarely get reduction on the bottom shelf  which is 5" off the bottom of the kiln.  I have had perfect reduction only once in MANY firings and most of the time I will have some pieces show total R and others will have half the bottom etc.  I keep notes about times and temp and my R readings but without college experience behind me I don't know how to fine tune that info to my best interest.  Overall my kiln usually fires within 1 cone top to bottom by the end - have that figured out - but the nice consistent R escapes me.  Guess I'll just have to be patient...

 

Diz

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One thing you could do now is reduce more-and see if this helps youe whole load-

If you do to much you affect climb (raise of temps) to litlle climb is fast and pots look bad.

I would error on the to much side and see if that helps at all.

Mark

 

One last note I have never seen a reduction in gas usage with my two meters-its more about fine tuning the damper to obtain reds than saving any money. I suggest looking at night at the color of the flame and how it licks out the lower spy plugs-this is leaned from doing not collage really-its self taught so you are in luck.

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Well - I am definitely self taught!  Some places say reduce around 1650 for body and then again around 9 for glaze reduction.  When I started I was told to do BR from 1650-1850 and then open it up a bit but try to keep it in mild R all the way to the end going heavier around cone 9 to 10 down.  A couple of times the kiln has done every step without me touching a damper or port - wish that kiln god would visit more often!  I rarely can get flames out my bottom peep, even with top port about 90% closed and my 4 primaries closed to only 1/4" open on each.  Once I close the primaries during a firing they stay at that setting til the end and I just adjust my top port only(also have a baffle shelf 1.5" below the lid to hold back the flames a bit).  Last summer I learned a lot with help from Mike at Continental Clay (a GREAT place for supplies ad help) but now I am focusing on improving my reduction.  Also my firings generally last 10-12 hours, if that says anything about my firings.

 

I'll stick with my auto sensor, and this summer work for reduction by looking at the spy holes and watching my numbers on my sensor.

 

One question - something I have never been able to manage - how do I stall the kiln during reduction? Mine just marches right through - and that may be the root of my problem.  I have heard that it should take 1 hour (stall) for R but mine can be as short as 1/2 hour as the temps march on.

 

Thanks for the help - much appreciated.  This sight is a goldmine for info - so freely shared.

 

Diz

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Well - I am definitely self taught!  Some places say reduce around 1650 for body and then again around 9 for glaze reduction.  When I started I was told to do BR from 1650-1850 and then open it up a bit but try to keep it in mild R all the way to the end going heavier around cone 9 to 10 down.  A couple of times the kiln has done every step without me touching a damper or port - wish that kiln god would visit more often!  I rarely can get flames out my bottom peep, even with top port about 90% closed and my 4 primaries closed to only 1/4" open on each.  Once I close the primaries during a firing they stay at that setting til the end and I just adjust my top port only(also have a baffle shelf 1.5" below the lid to hold back the flames a bit).  Last summer I learned a lot with help from Mike at Continental Clay (a GREAT place for supplies ad help) but now I am focusing on improving my reduction.  Also my firings generally last 10-12 hours, if that says anything about my firings.

 

I'll stick with my auto sensor, and this summer work for reduction by looking at the spy holes and watching my numbers on my sensor.

 

One question - something I have never been able to manage - how do I stall the kiln during reduction? Mine just marches right through - and that may be the root of my problem.  I have heard that it should take 1 hour (stall) for R but mine can be as short as 1/2 hour as the temps march on.

 

Thanks for the help - much appreciated.  This sight is a goldmine for info - so freely shared.

 

Diz

First I would need some info on your flat to suggest when to start a reduction

Lets assume it stoneware as thats usually what folks use.

1650-1800 is fine for body

for me in an all porcelain wares kiln I start at 1750 if I have reds

if not its around 1950-2000 and I keep the same reduction the rest of the way on my oxygen meter

I never adjust my my primaries only use the damper whether its my downdraft or updraft kiln-only adjust the damper. Now thats said I will do micro adjustment with a burner or two to keep it in zone as the damper moved a 1/32 can be to much one way or the other.

If I was firing your torchbearer I would damp it down more than you describe and do it sooner like 2000 degrees. My fires are all around 12-13 hours .I think you are under reducing if you never had a stall . You should be able to stall with a digital meter by closing the damper way down. I try not to ever stall kiln as 12 hours is a good melt  time for glazes . My fires slow down as the temp gets hotter like cone 9-11. This is the critical melt time as well.With a digital meter you can control the rate to be slow by damper use. Remember good reduction also will slow fire . It does not mater how much you close damper (you said 90%)It may take 98% or 70% what matters is the flame color and how to judge reduction by color and lick in lower ports.Once you get this down it should be very similar in most fires. If you cannot read this color fire at night so you can see it until you know it.

Mark

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Like Marc said, the oxy probe will do nothing to help with evening out reduction. That's a kiln issue, and your type of kiln has lots of evenness issues. It could, in theory, help with over all efficiency so you're not reducing more than you need to, but that would only work with a kiln that can handle adjustments without throwing everything else out of whack.

 

When I reduce, I stall out the kiln so it's not climbing in temperature at all, and let it reduce for 45 minutes. Then I put it into light reduction and start climbing again. With your kiln, I would go very slowly up to body reduction to try and keep the temperature even, then reduce the crap out of it, stalling it out. In a kiln that size it shouldn't be too difficult to get reduction throughout the kiln if you stall it out.

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Thanks!  I'll put your suggestions to use when I fire later this month.  I appreciate your time and the fact that you share your knowledge so freely.  It helps us all.

 

Diz

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High fire reduction is what I do weekly so talking about it is easy-

There are so few of us on this board that do this its great to exchange ideas and experience-I wish more here worked in this range but thats another subject.

mark

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Hi Diz..  hi all..   I tried my homemade version of an oxygen probe just like someone else had describe..  since the membership at guild I belong to didn't want to purchase the not so expensive $400 version direct from Australia mfg..  I built an exhaust manifold of sort that would funnel some of the gases going up the chimney and pass them by an automotive sensor I tapped into the flow with a nice clay collar to contain the sensor..  the readings I got on the cheap Harbor Freight digital meter just continued to climb as the sensor heated up it seemed..  in the 40+mV range..  then i swapped sensors to another used one and I didn't get any reading..  UH..  I was disappointed..   any tips out there?   thanks 

Joe

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