bad thermocouple on EvenHeat GT-18?

Richard Dubois · Post by **Richard Dubois** » Tue Mar 16, 2004 11:47 pm

Out of the blue on Sunday, my EvenHeat GT-18/RampmasterII started acting up. My usual System 96 full fuse to 1500F with a two-step anneal at 950 and 930F started giving a tack fuse and no apparent anneal. And the program ran its usual time, so it didn't abort early.

Is it possible that the thermocouple has decided to measure (say) 5-15% lower than before (I didn't touch it!)? That would be consistent with the tack fuse and no anneal (ie trying to anneal too low).

I tried a straight ramp to 1500F and all the elements came on etc. Anyhow, multiple attempts at a 1500F fuse have ended up with tack fuses. Of course, with the controller I have no independent way (other than how the glass behaves) to verify the temperatures. Never needed cones!

Any other possible causes? The thermocouple is the only thing I think can of that fits the evidence as I see it...

Richard

Stuart Clayman · Post by **Stuart Clayman** » Wed Mar 17, 2004 12:13 am

Richard,
I am looking at the wiring diagram for your kiln. It has 3 sets of elements and 2 relays. If the 3 elements come on then the 2 relays are working.
The problem can be in the thermocouple or in the electricity. A thermocouple can have a creep and slowly go bad, but usually not a big jump at one time. Is it possible that you hot the thermocouple before sunday when you were removing the glass or the shelf?
If it was during the summer when there was a large usage of electricity for AC there could be a drain on the power from the pole.
One thing that I would suggest that you check is to make sure that the thermocouple wires are tightly screwed down to the connector. Also check to see if the thermocouple wires touch the metal case at all.
I am assuming that your controller is not giving you any error messages. Can you figure out your ramp rate on the ramp up. If you are going 9999 to 1500 (or ASAP to 1500) do you know how long it takes to get to that temp. If it takes you 5 hrs then please change your ramp rate of 300Â°/hr to 1500. when you go 9999 it removes the error checking.. by going to 300Â° the controller might give you an error message if it can't go that fast.
You can e-mail me directly with the answers and if you give me your phone number I will call you and try and walk you thru a few things.

Stuart

Richard Dubois · Post by **Richard Dubois** » Wed Mar 17, 2004 12:33 am

Hi Stuart,

Indeed the 3 elements are working. None of my ramps up are faster than 1000 (going from 1250 to 1500). I do set 1500 going down to 950. My usual fire is

500 dph to 1000; 75 dph to 1250, hold 30 mins
1000 dph to 1500; 1500 dph down to 950, hold 45 mins; 100 dp down to 930m hold 45 mins; 200 dph to 700; off.

It's actually quite warm here in the SF Bay Area these past two weeks. Hard to believe I'm not getting the juice through! I put in a 200A service to the house for the kiln!

On my test ramp of 750F/hr to 1500, it took 1 hr 49 mins, but started around 125F (I hadn't waited for the kiln to get back to room temp to try this program), so I think the ramp times are internally consistent. It thinks it's going to 1500 and is about the right time interval. No error messages on the controller.

The kiln is cooling now after another test, so I'll take a peek in the morning and see if the t/c wires are looking ok. I don't recall hitting the thermocouple in recent history. I certainly have bumped it more than once in the year I've been using it.

The only other new thing over the weekend was trying a Ceramaguard fiber board for the first time.

I'll see how the thermocouple looks in the morning.

Thanks!

Richard

Stuart Clayman · Post by **Stuart Clayman** » Wed Mar 17, 2004 12:44 am

Bingo.. that is it.. the thermocuple is fine.. Put your shelf back in and things will be fine.. the fiberboard will not get as hot as the shelf will so things fire cooler.

The air in the kiln is still getting to 1500Â° which is what the thermoccouple is measuring. The difference is that since the fiber is cooler than the shelf the glass is not getting as hot. You can experminent with going slower to allow more time for the glass to get hot or else go to a higher temp when you use the fiberboard.

Richard Dubois · Post by **Richard Dubois** » Wed Mar 17, 2004 12:48 am

Not so easy. I was using the Ceramaguard as a drop ring on my regular shelf. Followed by a regular fuse on the shelf, then a fuse on a Duraboard drop ring. The latest tests were on my usual shelf.

So it isn't the presence of the Ceramaguard (I have used it in the last 4 fires). I was grasping that maybe its first fire to 1500 might have affected the thermocouple with outgassing or something, but that seems like a stretch.

Richard

Stuart Clayman · Post by **Stuart Clayman** » Wed Mar 17, 2004 12:58 am

Ok, lets go back to the thermocouple. when it cools down check it.. I will have a few other questions for you then and then somethings that I can walk you through.

Stuart

Tony Smith · Post by **Tony Smith** » Wed Mar 17, 2004 5:58 am

The RampMaster II also has a thermocouple offset option that might have been inadvertently set. It allows you to "tweak" your thermocouple by up to 50 degrees... it doesn't sound like that would be enough to cause what you're seeing, but you might want to check it anyway. It's under the "other" menu under tCoS. All three should be set to 0.

You might want to give Rob Bartlett a call (Bartlett Instruments makes the RampMaster II). (319)372-8366 http://www.bartinst.com. He'll be able to troubleshoot the contoller with you and perhaps give other suggestions.

Tony

Tony Smith · Post by **Tony Smith** » Wed Mar 17, 2004 7:45 am

Just one other thought... the only way your kiln would underfire is if the controller thought it was hotter inside the kiln than it really was (duh). Any chance you have a top element that's sagging near the thermocouple?

Tony

Richard Dubois · Post by **Richard Dubois** » Wed Mar 17, 2004 10:56 am

A quick check of the kiln this morning - and it looks to me like the thermocouple is fine - the ends are still touching; nothing looks out of the ordinary. And I can't see any sag of the top elements, certainly not to the extent of being anywhere close to the bottom of the slots they're in.

tCoS was zero (I had not touched it).

Richard

Tony Smith · Post by **Tony Smith** » Wed Mar 17, 2004 11:32 am

RichardDubois wrote:A quick check of the kiln this morning - and it looks to me like the thermocouple is fine - the ends are still touching; nothing looks out of the ordinary. And I can't see any sag of the top elements, certainly not to the extent of being anywhere close to the bottom of the slots they're in.

tCoS was zero (I had not touched it).

Richard

It sounds like it's time to call Rob Bartlett.

Tony

Richard Dubois · Post by **Richard Dubois** » Thu Mar 18, 2004 3:47 pm

This reads a lot like the "Weird Temp Issues" post. I have also concluded my thermocouple is failing and have a couple winging their way to me from Ed Hoy. We'll see how that goes.