Thermocoule precision?

[David Williams]

Time for a group hug... Everybody???

(where's David?)

Tony :biggrin:[/quote]

Yep. I'm here. See, this is the thing. My wife might not understand if she finds I've been hugging men in bathrobes on the internet. Okay. Hey fellas gotta go...

[Lauri Levanto]

Did I poke beehive

The kiln is a man's best friend - before the dog.
We all love ours, and defend it.

My apologies for the wrong estimate of precision.
From now on I trust my thermocoupe to give
the temperature of the thermocouple.

The temp of the air is crucial at low temps.
At the upper range the radiation rules.
I noticed it yesterday when I had to put my hand
into a 700 C kiln to add some cullet

The sun shines equally to the good and evil
so does the kiln radiation. The shied of the TC
is luckily of the same whiteness as my mold materials
and absorbs the radiation the same way.

The glass in my mold behaves differently. It transmits
much of the radiation to the inside of the mold,
absorbs some and reflects the rest.

All this takes the ramping and soaking we are talking about.

COOLING

Jus now I have a simple open form in mu kiln
There id 6 kg glass in a 5.2 kg mold.

Almost half of the heat is stored in the mold.
It is a flat, openface mold with shallow sides.
It has only two ways to loose heat: thru the glass
and thru the shelf. That is why the mold thicknes
is included in the annealing formulae.
In the annealingphase I have to use top elements
toslow down the heat loss - to a rate that matches
the heat transmission from the bottom.

When I cast in a tall deeep form, there is very little exposed
glass area. All the heat must be lost thru the mold walls.
If they are of uneven thickness, uneven cooling
is unavoidable unless it is very very slow.
In fact I am annealing the mold, more than the glass.

HUGGING

Tony,
I am in cold and dark Finland.
I miss you all.

-lauri

[Don Burt]

Just like flavored Alka Seltzer. The grape was yucky

You can make your own grape fizzy with HF and Bullseye 0147 frit. If you drink a lot of it you may need some calcium supplements though. (Another use for your casting plaster).

[rosanna gusler]

you know ron, i could have done without seeing one of my childhood favorites listed on a website with OLD TIME in the title. sheesh. rootbeer was my fave. i wish i still had that fizzy dispenser. creepy crawlers was another goodun. used to burn the crap out of ourselves with that one. rosanna

[Hugo Gavarini]

Sean wrote in another thread:
". I'm positive the
glass is being fired at the temp. the controller is reading.

How accurate are the controllers really?
I trust it to give pretty much the same reading at the same temperature. If I remember right the thermocoule
came with 10% accuracy. Over a 800 C range
it may be 80 C off at worst.
Not to mention the difference between glass and thermocouple.

Just now I have a 6 kg (12 lb) casting in the kiln.
Cooling down AFAP, the small thermocouple head
cools faster than thhis bulk of glass.

The veterans keep saying that kiln are different
and the temps given here are but indicative.

Is it kilns or thermocoules that are different?

-lauri

Hi Lauri,

My belated two cents.

When I had to know my kiln temperature distribution I used the Bullseye procedure to calibrate our small vitrigraph (which we have modified to a test kiln). Besides, I have got a temperature profile using orton cones. Both, Bullseye and Orton give calibration advice and support literature through their sites.

Of course, knowing actual glass temperatures would be almost always an indirect measure. Orton cones measure not only temperatures but also heat work which is the actual transformation cause in warm glass processes.

[Stuart Clayman]

I recently had to set up a new L and L kilnfor someone. Once I got it set up and turned on, the controller read 121. Now, I know it is warmer in Florida, where I was at the time but it was not that hot. I called the manufacturer and asked what was up with the temp reading. I was told that they set via the software for the temp to read 50 degrees off at lower temps because their thermocouple was sheathed in ceramic and once the kiln got to higher temps the readings would be correct.

Also on the Bartlet Boards, the temp shown is the average of the last 8 readings and the board reads the temps 8 times a minute.

[daffodildeb]

Yup--they were horrible, IMHO

[Hugo Gavarini]

Besides Bullseye and Orton procedures to tell your actual kiln temperature mapping, you can test your thermocouple for some points at high temperature. Some metals melting point would be of use. For example, pure Aluminium is 1220°F (660°C), pure Silver is 1761°F (961°C) and Sterling Silver is 1640°F (893°C).

A small piece of these metals have to be arranged close but not touching the thermocouple tip. You will have to watch to witness the state transformation. Beware your eyes!.

[Tony Serviente]

Of course this would not work for enclosed castings, but anyone use optical pyrometers? They should be able to give a direct surface temperature measure of the glass. Only problems I can see is that you have to pop the lid to shoot a temp, and if the glass is glowing there is the issue of aim, the laser pointer would be impossible to see so you would have to pre aim. Wonder if anyone has tried this.

[Bert Weiss]

Of course this would not work for enclosed castings, but anyone use optical pyrometers? They should be able to give a direct surface temperature measure of the glass. Only problems I can see is that you have to pop the lid to shoot a temp, and if the glass is glowing there is the issue of aim, the laser pointer would be impossible to see so you would have to pre aim. Wonder if anyone has tried this.

Tony

When I was growing up, my dad sold Ircon optical pyrometers. They can make them to read the hot glass temp or to look through the glass and read the refractory temp beneath the glass. I imagine that you could mount one with a quartz window and take readings during a firing.

I never used one in my kilns though. I was always too far away from home to borrow one. Dad is no longer with us.

[Tony Serviente]

I've had my eye on one for a while that reads from minus 25 to 1500F. It is hard for me to justify getting one on the basis of need, since I am doing what I want in the kilns without one, but it would sure be a cool learning tool, and might be useful for bigger projects than I am doing now. I guess the trouble is, I really like tools, especially if they have a digital readout.