"mc" <look@www.ai.uga.edu.for.address> wrote in message 
news:0XUli.23205$09.10960@bignews8.bellsouth.net...
> Any thoughts about how to sense temperatures up to 1400 C inside a 
> kiln, for purposes of logging the data or feedback to the 
> microprocessor that controls it?

Don't re-invent the wheel - my company has already done this. We can 
supply you with an S-Type thermocouple designed specifically for use in 
a kiln and is good for up to 1600C. Check out www.autoflame.com or 
e-mail me and I'll put you in touch with our sales chaps.

It is designed for use with our exhaust gas analyser but you could 
easily use it with your own circuitry - you just need to be able to 
measure from about 0 to 17mV. Bear in mind that 0V is not zero degrees.

On Sat, 14 Jul 2007 02:39:55 GMT, the renowned Jonathan Kirwan
<jkirwan@easystreet.com> wrote:

>On Fri, 13 Jul 2007 21:36:42 -0500, Spehro Pefhany
><speffSNIP@interlogDOTyou.knowwhat> wrote:
>
>>On Fri, 13 Jul 2007 19:57:26 -0400, the renowned "mc"
>><look@www.ai.uga.edu.for.address> wrote:
>>
>>>Any thoughts about how to sense temperatures up to 1400 C inside a kiln, for 
>>>purposes of logging the data or feedback to the microprocessor that controls 
>>>it?
>>
>>Thermocouple. Type S or R in an alumina protection tube if you want
>>long life and good performance. 
>
>Alumina (sapphire-like) melts around 2000C or so, though I think I'd
>only safely consider it usable to 1700C. 

As he only needs to go to 1400&#4294967295;C that would seem to be sufficient.
There are cheaper ceramics for lower temperatures that might be
marginal at 1300-1400&#4294967295;C. 

> The OP might refer to:
>
>http://www.omega.com/ppt/pptsc.asp?ref=RAT_SAT_BAT&Nav=tema13
>
>to see what your suggestion looks like and get an idea as to pricing.
>
>I don't know what the thermal response time of a kiln looks like, but
>I suppose it's on the order of minutes.  I'd guess the response time
>of this kind of assembly should be fine with PI or PID.  Positioning
>might be important.
>
>Offhand, Spehro, it would seem to me that the finer gauge thermocouple
>is better, because it will respond faster.  

In this case, response time will be limited by the thick and heavy
protection tube, but yes that's true. At least the extra pole will
probably not be significant from a control pov. 

>But do you know why
>someone might choose the heavier gauges?  [They cost a LOT more
>(platinum isn't cheap.)]
>
>Jon

There are some metallurgical effects, IIRC, depending on the
atmosphere the metal is exposed to, but typically I think AWG30 is
okay for a situation like this for moderately heavy use. Stuff
diffuses in and out and the alloy diffuses across the junction to some
extent at those temperatures. You might want a heavier gauge if it's a
big industrial installation. There is no significant electrical
difference, of course. The Pt is recycled. 

Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

mc wrote:

> Any thoughts about how to sense temperatures up to 1400 C inside a kiln, for 
> purposes of logging the data or feedback to the microprocessor that controls 
> it?

Buy a thermocouple (Platinum/Rhodium from memory) designed for the
purpose ?
These have a low mV output (12-16mV IIRC), that is slightly non-linear
so nothing too complex. Needs a precision amplifier, and a correction 
table, if you want an accurate display over the whole range.

-jg

On Fri, 13 Jul 2007 21:36:42 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>On Fri, 13 Jul 2007 19:57:26 -0400, the renowned "mc"
><look@www.ai.uga.edu.for.address> wrote:
>
>>Any thoughts about how to sense temperatures up to 1400 C inside a kiln, for 
>>purposes of logging the data or feedback to the microprocessor that controls 
>>it?
>
>Thermocouple. Type S or R in an alumina protection tube if you want
>long life and good performance. 

Alumina (sapphire-like) melts around 2000C or so, though I think I'd
only safely consider it usable to 1700C.  The OP might refer to:

http://www.omega.com/ppt/pptsc.asp?ref=RAT_SAT_BAT&Nav=tema13

to see what your suggestion looks like and get an idea as to pricing.

I don't know what the thermal response time of a kiln looks like, but
I suppose it's on the order of minutes.  I'd guess the response time
of this kind of assembly should be fine with PI or PID.  Positioning
might be important.

Offhand, Spehro, it would seem to me that the finer gauge thermocouple
is better, because it will respond faster.  But do you know why
someone might choose the heavier gauges?  [They cost a LOT more
(platinum isn't cheap.)]

Jon

On Fri, 13 Jul 2007 19:57:26 -0400, the renowned "mc"
<look@www.ai.uga.edu.for.address> wrote:

>Any thoughts about how to sense temperatures up to 1400 C inside a kiln, for 
>purposes of logging the data or feedback to the microprocessor that controls 
>it?

Thermocouple. Type S or R in an alumina protection tube if you want
long life and good performance. 


Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com