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MarkS

Another Pyrometer Question

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I've been trying to decide what's going on so I thought it would be best to get some knowledgable persons opinions.

I did a glaze firig last weekend and use my new toy - a "homemade" pyrometer.

I noticed the temp build about 200/hr until the kiln sitter( with a ^7 cone) tripped at which time the temp read 1840.

I pushed the button back in as my ^6 witness cone had not bent. The temp dropped about 75 and after about 45 minutes the cone was well bent so I shut it off. The hottest the pyrometer ever shown was the 1840. Total firing time was about 9 1/2 hours.

A recent ^04 bisque firing was a similar scenario although max temp was about 1650.

Now my dilemma. Is the thermocouple bad or maxing out? Or are the temp readings correct and the elements getting old?

I welcome your thoughts and opinions.

Thanks!

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Guest JBaymore

I've been trying to decide what's going on so I thought it would be best to get some knowledgable persons opinions.

I did a glaze firig last weekend and use my new toy - a "homemade" pyrometer.

I noticed the temp build about 200/hr until the kiln sitter( with a ^7 cone) tripped at which time the temp read 1840.

I pushed the button back in as my ^6 witness cone had not bent. The temp dropped about 75 and after about 45 minutes the cone was well bent so I shut it off. The hottest the pyrometer ever shown was the 1840. Total firing time was about 9 1/2 hours.

A recent ^04 bisque firing was a similar scenario although max temp was about 1650.

Now my dilemma. Is the thermocouple bad or maxing out? Or are the temp readings correct and the elements getting old?

I welcome your thoughts and opinions.

Thanks!

 

 

 

Mark,

 

For reference:

 

http://www.ortonceramic.com/resources/pdf/wall_chart_horiz.pdf

 

 

At 200 F per hour the cone 6-7 should have been showing you something in the top end of the 2100 to low 2200 F range. (Remember... cones do not measure temperature, but measure heat work.) Something is up.

 

Are you using an extension wire on the thermocouple? If so... is it thermocouple extension wire or simply some copper wire?

 

If you are using copper wire to extend the length ... then you have created extra thermocouples at the copper junctions witht the actual thermocouple... which are adding or subtracting electromiotive force on the readings.

 

 

best,

 

......................john

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John,

The thermocouple and wire was an Ebay find. But I'm not sure about the wire. Could it make that much difference?

I didn't consider 9 1/2 hours total firing time unreasonable.

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Guest JBaymore

Mark,

 

Aha... EBay huh?

 

Is it an analog or a digital meter unit?

 

If it is analog, on the dial face somewhere in TINY print it should say something about "+/- X % of full scale deflection". Check that X percent. That percentage number is important. It tells you what the error factor is for any given reading you are looking at.

 

If the analog meter shows a top reading of 2 500 F (a lot of cheap meters do) and that percentage is 2% (common for cheap analog meters), then the accuracy is plus or minus .02 x 2500 = or 50 degrees F. So if you look at the reading on the dial face and it says 1000 F..... it could actually be anywhere between 900 F and 1100 F. Effectively useless other than to simply see if you are getting hotter, getting colder, or (maybe) stalling.

 

And that accuracy is IF the meter with the thermocouple and extension wire has been calibrated correctly. If not... the accuracy is even worse. Calibrating analog meters is a whole subject in itself.

 

What type of thermocouple is attached to the meter unit? Type K? Hopefully the thermocouple and the meter input are matched. On a meter set up for one type, if the thermocouple is actually another type... that too introduces significant errors.

 

Digital meters are sometimes more forgiving and some have automatic calibration and thermocouple matching functions. But not always.

 

As to the copper wire instead of the correct type of thermocouple extension wire... yes... I can induce a huge inaccuracy. And as that secondary thermocouple it creates changes temperatrure THERE..... the inaccuracy also changes.

 

best,

 

......................john

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Yes, it's a type K thermocouple. Mated up to a unit I put together with a PID.

Looking at getting another from Omega and the correct extension wire.

We'll see....

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Yes, it's a type K thermocouple. Mated up to a unit I put together with a PID.

Looking at getting another from Omega and the correct extension wire.

We'll see....

 

 

You might be able to adjust your pyrometer, too.

 

Sincerely,

 

Arnold Howard

Paragon Industries, L.P., Mesquite, Texas USA

ahoward@paragonweb.com / www.paragonweb.com

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