Bill Kielb

Did you add cones to the firing and you using a final segment firing speed that corresponds to the Orton chart to hit a particular amount of heat work?

CO (Carbon monoxide) is very dangerous to human life but in fuel based reduction a necessity to get the reduction reaction. CO is not explosive, it is the end result of a very dirty (fuel rich) flame. Folks who do reduction generally wait until approximately 1600 f degrees to go into early reduction. This is often called body reduction or clay body reduction before the glazes have begun to melt. So why 1600 degrees? Before one introduces excess gas into a kiln to produce a dirty flame they wait for the temperature of the kiln to be above the self ignition temperature of the fuel so as not to build up enough raw gas to reach the lower explosive limit (LEL) of the gas. So that’s a mouthful but .........only still very basic reduction. Reduction in electrics can be had with fuel / carbon monoxide or in some cases chemically with silicon carbide local reactions. Reduction atmospheres in electric kilns tend to corrode elements aggressively so Neil’s question is spot on. Pictures of your kiln will help determine how this reaction was being obtained. Reduction firing is fairly simple and folks do it daily with great result yet it only affects a handful of metals with respect to color and carbon trapping is a thing decoratively as well. Much has been said about reduction, most of it with elements of correctness but as you have likely noticed much of the information can be partially correct or perception based. IMO, This is a solid description of the process and a good start: https://ceramicartsnetwork.org/daily/firing-techniques/gas-kiln-firing/demystifying-the-reduction-firing-process/ From there fuel based safety, carbon monoxide safety, gas train safety are all things one ought to learn when firing a gas kiln, especially in reduction. Again, these things are relatively simple unfortunately one can find good and not so good explanations so locating good credible reading material is a thing. unfortunately much of the above is from 2018 / 2019

If it’s transparent then definitely worth the trial. You might have a cool combination. Maybe test tile time. My experience has only been with fairly opaque colors and layering with stroke and coat. The dragon on the mug below was created with layers and fired down.

Stroke and coat is a lowfire glaze that can fire to cone 10 if memory serves me and .......... Is opaque. Are you sure you want to cover your underglaze with it?

Just glad he needs no offsets. I take it you do not believe the new hollow tubes are a better overall idea?

Just curious and apologies if it’s already been stated, the programs that have run have been the automatic cone fire? And looking at your data and some familiarity with The Genesis control. Zone 3 in your firing ended particularly cooler than the rest so my thought is: the controller has an automatic lag function which I believe delays the other zones while the cooler one catches up. We used to have the ability to use the center element to help with the top or bottom to catch up, but I believe this has been replaced by the automatic lag function. Anyway, maybe some food for thought if there is an obvious reason that zone is cooler (open site plug, misaligned lid) it might have the effect of extending the firing too long. Sorry, just brainstorming a bit here. Glad to hear the protection tubes have gone by the wayside so to speak, which brings one last thought as to how deep are the actual thermocouples embedded into the kiln so they all sense equally and as accurate as practical. Just thinking........

I wonder if your base offsets for the thermocouples (covers) were entered correctly? This may or may not be something L&L would do but rather specify to Bartlett to be preprogrammed. Definitely worth checking what they are and what they ought to be. Sorta matches your problem with the whole kiln over firing.

Maybe dial in those offsets now and see how they hold up

Funny, see this all the time actually. Why not take these up to 1000c (just asking). Hard to understand these from your previous data as your PI differential seemed to be growing non linearly: Time (min)/Kiln (C)/Pi (C)/deltaT (Pi-Kiln) 0/14/11/-3 75/90/103/+13 210/223/265/+42 285/300/350/+50 My thinking is the Berm and Rex C are the newest so their values stand a chance of being correct and they are close enough to the PI board so an offset in this range will be a conservative choice.. so going off the PI, +10 - bentrup, (Hi limit) -6 Berm, -9 Rex C 100 (something on that order to get them all tracking similarly) They arę all fairly close I would test them to a higher temperature to make sure no surprises and confirm with cones. Confirming with cones by the numbers would be important so in the last 100c of the firing you need to go the prescribed rate to be meaningful. Check that the kiln did actually go that rate, many kilns for various reasons lose the ability to do so, so your firing record becomes important. As time goes on if you always fire your last segment at the appropriate rate and use cones you might slide these up or down a few degrees. If you don’t fire with the correct rate in the last segment then it will be impossible to get a feel for the actual heatwork. Sorry for your difficulty, but this is real world, kiln controllers are accurate enough for their use and firing clay is fairly tolerant, but real world accuracy, not so much when processes cannot tolerate minor differences in temperature. Using the PI value seems reasonably conservative after offsetting your high limit to match. Now is a real good time to see how your SSR cooling is working BTW.

Good meter readings and the s thermocouple chart are likely the most accurate thing you have. It’s too big of a spread but starting out, checking the difference with ice water and boiling water might have given you some idea of which is more correct at low temperatures or a magnitude of the difference. The Bentrup has functioned well for firing and is the conservative reading thus far which means I would err towards its reading for offsets given no other choice. Both require setup offsets, neither are likely certified tolerance items.

Someone once said a few posts ago: “Doubling inputs, extra junctions etc..... are always discouraged and testing one case in one instance may or may not indicate this will provide acceptable readings over its lifetime. That all said, this often does work and I suspect you will initially make this operational. Since it is a safety circuit though I would encourage you to just convert this to current loop or other established methods that are approved the world over. “ My feeling is the bentrup is likely the better reading. I would measure the output voltages of all with a known very good meter and compare it with an S thermocouple chart. Record those values as well they should be the most precise......... but ......... it needs to be a high quality calibrated meter, good connections to the millivolt level. The reality, none of this stuff is likely certified as calibrated so you will not know the potential error in each item. Bentrup, PI, or your meter so .......... If I had confidence in the voltmeter then the chart values likely will be most correct and I would enter offsets in each accordingly. At some point you need confidence in one of those things to develop sensible calibration offsets for the PI and the bentrup.. right now you have a one cone or better mismatch which is significant. Without that confidence, my thought would clean bentrup readings are most conservative of the two given clean tight direct wiring. Anything else on the switch may change over time due to the smallest of unpredictable changes, cabinet temperature, switch wear, noise on the line, we don’t know.

IMO I think they would be fine certainly to try, it’s not as if this element is gonna fly out of there. We have elements grow out several inches from kilns with worse slots after many firings and we just torch them back into place neatly. Plenty of internet videos on doing that. I would try it out and I believe it will not be a whole bunch of trouble. If my thought is wrong or if you discover they are worn it only means you will simply need to replace your elements sooner than later. This could be a good opportunity to get all your parts. I like your center pin best . Not sure I would need more than two of those about 1/3 of the way in from each end. You could always take a long straight pin and rotate it in far enough so it’s embedded in the brick and catches behind the top of the element holder. In my experience the element holders on those kilns allow elements to grow and shrink pretty uniformly. Pinning it firmly at one point often inhibits this movement and causes more trouble with unequal growth. I would be more concerned the pins are imbeded towards the center of the brick and not out towards the face so you do not damage the outside face of the brick. My experience, I have pinned far worse.

Since mold is everywhere and I mean everywhere I try and minimize where it can grow. So moisture, temperature and available food source because I feel I can never make it go away completely. Peroxide seemed to be something that could provide a relatively benign method of keeping the spores in check since it ends up as water. Bleach can be an irritant in itself for many. So for me a person without any special sensitivity cleanliness and good practice gives me reasonable confidence. I don’t have any bags of moldy clay (at least visually) and if I did I would treat the mold or discard the clay carefully minimizing spreading the spores. In a classroom environment I think I would do a mold count and yes determine the type, especially if I had folks say they were being affected by it.

If you measure the elements with an ohm meter you should be able to tell where they are in their lifespan. A 10% increase in resistance from new means they are ready for replacement. I am pretty sure the easy fix for these holders is to cut out the old ceramic element holder and install new, cementing it in place using a tiny amount of appropriate high temp grout / patch / cement else some kiln brick removal is in order. Probably best to have ready when you do replace the elements. @neilestrick has likely done this many times over the years. For now I think you could use it and if it crawls out you could get some pins across the front so it does not crawl out too far if and when needed until you replace the elements.

Somebody has got to help soon, I don’t want to learn PI programming and it’s nuances! @liambesaw used to do some I believe.

Interesting, it will be fun to see what final form you eventually decide on. Center off switches, I would not have guessed. When ready with the final form of this, I would suggest creating the schematic which should allow you to perfect all the safety aspects. Fusing, wire sizes, interlocks etc.....

No I think I get it, and it’s something being developed. It sounds like the Rex will be your high limit and moved between kilns, unless you have two of them.

Hmm, the Rex c 100 is not programmable so starting it from the pi with a program would be a chore and it has 4-20 ma input but does not appear to be able to communicate that with anything else. Will that be they safety for each kiln and you will simply move it from one to the other .......... or will you add another controller? If so, you might pick a control (eventually) that has more capability at some point and give thought to each kiln having its own pid control tuned for that kiln and all the rest that goes with that. Might be worth contemplating.

This is all very true, although I believe the oven program is simple without significant PID tuning. One important design thought here is when we design things the safety for the device gets installed on the device. So if I were to take your two kilns, the safety would be mounted to the kiln in the form of a digital controller which transmitted the temperatures back to the pi. Of course at minimum this controller would have a high limit which on its own shuts off the kiln, especially on loss of power, so fail safe (not fail secure) for all interlock wiring and relays. Actually it’s customary to have a designated high limit, independent of the control, so a designated high reliability high limit as well. Relying on the pi programming to intercept all possible errors is not really good practice. Once you add a controller to the mix, may as well make it a pid control and just select it from the pi. Tune the pid in the separate temp controller to match the kiln thermodynamics (most have auto tune)

How about this for simplicity and a hardwired solution. 2 males (females) 1 female (Male) maybe 10.00 bucks on Amazon, virtually all your issues go away. No current loop till you want to learn about it. Current loop stuff is ready made and pretty cheap as well. Most temperature controllers have 4-20ma inputs as standard. I think I would put the male on your temp board and females on each thermocouple that way a dangling thermocouple would not be easily shorted against something. https://www.automationdirect.com/adc/search/search?fctype=adc.falcon.search.SearchFormCtrl&cmd=Search&searchquery=Type+k+transducers&categoryId=850116&TxnNumber=-1&searchqty=10&start=0

My opinion:, adding junctions is never good. The reason? Which will be the cold junction we will calibrate from? Ultimately it is the first one attached to the temperature board that you purchase for the PI. Alternating polarity only adds lots of junctions and couples which defeats the properties of the cable. Compensation cable acts like thermocouple wire at 200f or below so the greatest accuracy will always be as if this entire assembly acts as one super long thermocouple which means the polarities will match along its entirety. Using isotherm blocks and compensation cable minimizes this when junctions are added but the signal is often microvolts per degree f so a continuous extension cable with maybe 100 ohms resistance max (50 ohms each way) is likely the most anyone would venture before losing accuracy. Maintaining nanovolt voltage drops across well made isotherm junctions made of the same materials as the compensation cable might be argued as doable, but an ordinary switch, along with dissimilar metals, not likely. Switching will generate some noise for sure and the unloaded thermocouple will likely cause a fairly large swing upon switching so off cycle usage is likely the way this will work. Since your switch is likely not - make before break - you will likely add a resistor at this junction to drain the open thermocouple and possibly one across the moveable contacts else your temperature board if active during switching will sense a thermocouple burnout during switch operation. So again, alternating polarity makes this worse in my mind and for any type of safety circuit, just change it to current loop and transmitters or other suitable transducer. In the meanwhile you likely can get it to work for you, just as Alpine did many years ago but all that stuff was analog and we ended the firing by watching cones so plus or minus 20 degrees on the meter was just fine. And of course there was always that warning, over 1500 degrees,, don’t touch that switch! Anyway, once thermocouples are converted to a more robust signal, they are super easy to work with, dependable and from there extended as far as you like. After that you are pretty free to innovate and make cool dependable stuff.

You will probably get this to work, but by now if you have googled around the world you realize it is not the way to do this. Since this is going to be a safety device, I am going to do my very best at giving you some reasons it is not done: Most tcouple circuits contain an op amp circuit that also contains a cold junction reference to improve the measured accuracy. This circuit also generally contains a means to test for tcouple failure or burnout detection using pull up or down or both resistors. Finally this basic tcouple op amp is usually floating. Adding a second passive or active input is prone to: out and out error, drift, ground loop currents, and system noise. Doubling inputs, extra junctions etc..... are always discouraged and testing one case in one instance may or may not indicate this will provide acceptable readings over its lifetime. That all said, this often does work and I suspect you will initially make this operational. Since it is a safety circuit though I would encourage you to just convert this to current loop or other established methods that are approved the world over. A little reference on a common tcouple op amp, interesting reading but also shows how complicated things can become. https://www.ti.com/lit/an/sbaa274/sbaa274.pdf?ts=1619033246467&ref_url=https%3A%2F%2Fwww.google.com%2F

Now I realize why I am a DDC / PLC guy. After reading through this, I am less inclined to learn PI / Arduino stuff. I’m sure you will get it soon ....... of course PLC stuff is awfully flexible ....... and web enabled ......

If it has type bigger than 9 point and isn’t printed on one large folded sheet, I give them four stars to start. Proof read and fix, they get five stars from me.

https://learn.adafruit.com/thermocouple/arduino-code Still not a PI guy, but this may help. Started reading about the 31855 and noticed a bunch of interesting info from reducing noise to available libraries. Looks like it ought to be easy to get readings from the board. As to variables in the code and their use and mapping I would just need to get an understanding of the code written and the hardware. Some good stuff on thermocouples there though.