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Tips, Techniques, and Questions -- Technical questions or tips

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  #1  
Old 2012-01-02, 4:49pm
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Default Thermocouple Question

I have been trying to figure out why my kiln is not heating up to the temp set on my controller - for example if I want the kiln it at 940 degrees I have to set the controller at 1000 degrees in order to get the controller to show 940 - it is consistent in being off 50-60 degrees no matter what temp I am trying to obtain. I have tried several temps and it is consistently off.

I have made sure the thermocouple is inserted fully in the kiln. What I did notice is that the "ceramic" coating has broken in two - a split completely all the away around - could that cause the misreading of temp?

This has just started - I was fusing up until the holidays and I am trying to get back to making some beads but now I don't trust the temp for annealing.

I thought I would ask here - I tried calling the dealer but it is a holiday

Thermocouple on back of kiln - in as far as it will go.


Thermocouple inside of kiln- the coating is broken around in one place and I have them put together with no gap.


I appreciate any input.

Happy New Year!
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  #2  
Old 2012-01-02, 6:05pm
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I would replace the thermocouple. They aren't all that expensive.

Robert
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  #3  
Old 2012-01-02, 6:16pm
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Thanks Robert - I was thinking the cracked encasement on the thermocouple could be my problem.
I will get in touch with the dealer and get a new one.
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Last edited by C-Ann; 2012-01-03 at 5:47am. Reason: change spelling
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  #4  
Old 2012-01-02, 8:21pm
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Nope, wont hurt a thing.
It is a bit corroded though and the twisted end not cool.Is it welded at the tip ?
Take a wire brush to the end and clean it up a tad.
Also with no thermocouple block on the outside part the heat could have melted the sheathing, if the wires touch back there its not good.

Mike
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  #5  
Old 2012-01-03, 12:38am
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It looks like it may be inserted too far into the chamber to me. Most reccommend about an inch sticking out.
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  #6  
Old 2012-01-03, 2:58am
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Looks like the junction on the thermocouple broke off and someone twisted the wires together.

A thermocouple consists of two insulated wires with one junction. As another asked is the end welded? i.e. the weld forms the junction between the two different metal alloys.

When twisted there will be multiple points of contact that form many individual thermocouples which will vary as the wires heat up and cool down and make and break some of these connections. i.e. if the wires are not insulated.

As stated above, buy a replacement thermocouple.

Last edited by Alaska; 2012-01-03 at 3:00am.
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  #7  
Old 2012-01-03, 5:36am
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Quote:
Originally Posted by cheng076 View Post
It looks like it may be inserted too far into the chamber to me. Most reccommend about an inch sticking out.
I am going to call the dealer later today and order a new thermocouple.
In the meantime I will try a cycle with it in that 1 inch placement - can't hurt to try. I have always used it as it is placed now.
Thank you for your input
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Last edited by C-Ann; 2012-01-03 at 5:52am. Reason: wording change
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  #8  
Old 2012-01-03, 5:38am
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Quote:
Originally Posted by GLASSFREEK View Post
Nope, wont hurt a thing.
It is a bit corroded though and the twisted end not cool.Is it welded at the tip ?
Take a wire brush to the end and clean it up a tad.
Also with no thermocouple block on the outside part the heat could have melted the sheathing, if the wires touch back there its not good.

Mike
I will look and see if it is a weld and before I try the 1 inch sticking into the chamber I will see if cleaning it a bit will help too.
The kiln is as it was built and I will have to research what a "thermocouple" block is
Thanks for your input
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  #9  
Old 2012-01-03, 5:45am
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Quote:
Originally Posted by Alaska View Post
Looks like the junction on the thermocouple broke off and someone twisted the wires together.
Thanks for your input

The kiln and controller are as I received them and have never been repaired - there is a crack in the coating before the twisted wire that I don't know if I did or not since I rarely touch (try to avoid!) the thermocouple - the twisted wire at the end has always been there.

I am thinking after 7 years or so the thermocouple has maybe met it's life expectancy....I do mainly fusing with a little lamp working thrown in.
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Last edited by C-Ann; 2012-01-03 at 5:51am. Reason: typo
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  #10  
Old 2012-01-03, 11:29am
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The piece that is cracked in the picture is ceramic insulation to keep the individual wires from shorting out. About the only material that stands up to the heat. I can't tell from the pic but usually that ceramic will have 2 holes down the length that the TC wires go through.

While the kiln has never been repaired it probably has been moved and or worked around. As you have no 'thermocouple block' the thermocouple is free enough that it may have been inadvertantly pushed into the kiln chamber by accident. The connecting wires are solid conductors and are stiff enough that tension on them could push the TC into the kiln chamber if the insulation is not packed really good around the ceramic and in the hole. The 'thermocouple block' is a little cube, generally, of ceramic that has some screw connectors mounted in it that allow the heavier thermocouple wire to be connected to the red and yellow wires that go to the control.

New TC will probably fix the problem and they aren't very expensive. I'd guess maybe $15 or less for TC and block together.
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  #11  
Old 2012-01-03, 1:57pm
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I would like to thank everyone for their ideas and input - I appreciate the sharing of knowledge and I am learning too!

I did a quick look this morning before running errands and the ceramic covering the wire is actually 3 individual pieces on the wire - so they are not "broken" but cut to fit to cover the exposed wire.

The kiln itself has never moved but the thermocouple wire has been hanging around for almost 8 years........a jiggle here and there!

I used a small brush to clean the twisted exposed wire and it is not welded to anything - it is two wires twisted together with the open loop before the twist.
It is now only extended one inch into the kiln and tonight after chores & dinner I am going to try firing it again to see if it made a difference.

I do have a call in to the dealer that I made at 9 am Pacific time and I am waiting for a call back - all I wanted was to order a new thermocouple and I even know I need a "Type K" per my paperwork....But I need to talk to someone in the warehouse I was told.

The instructions on the side of the kiln say to fully insert the thermocouple now that I have really looked at the setup -


I believe that this must be what is supposed to be the "block" since it is what fits up at the hole against the kiln when the thermocouple is fully inserted into the kiln.
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  #12  
Old 2012-01-03, 6:00pm
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This is what a welded tip looks like for a Skutt 8 gauge replacement thermocouple.




The matching base (back side) fits this thermocouple. This is the side that the wires connect to. The thermocouple plugs into the non pictured side.



The base is about $6 and the thermocouple $14.
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  #13  
Old 2012-01-03, 6:18pm
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Thank you Alaska for the excellent visuals! I like the base and it makes perfect sense - just like the welded tip.

I didn't get a phone call back today - maybe tomorrow. I am going to go surfing to see if I can find a online source for a replacement thermocouple for my kiln & a spare too.

The test didn't work either with the thermocouple being only a inch in the chamber - the temperature was even further off.

I appreciate everyone's time in posting their advice and thoughts.
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  #14  
Old 2012-01-03, 6:39pm
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The base came from Clay Art Center in Tacoma, WA. You will have to ask for it as an Oval Kiln Connection Block. And made sure that it fits your selected thermocouple.

http://www.clayartcenter.net

Give them a call and see if they stock the 8 gauge Skutt. Bought the K type here locally at a ceramic shop. Use these both in the ceramic kiln and glass annealing kiln with a Fuji PXR-3 controller and have not had any issues.
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  #15  
Old 2012-01-04, 10:33am
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Thanks for the information Alaska - I will get in touch with them.

Here is a link to a site I came across last night that I thought had some interesting information - no endorsement for any company just the info content.
http://www.bigceramicstore.com/information/Tip89.htm

I did get my phone call first thing this morning from the manufacturer of my kiln and they were very helpful.

I will post when things are "heating up" again.

As I stated before I appreciate the advice and information.
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Old 2012-02-09, 12:37am
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Default Thank You Jason at Arrow Springs

I just wanted to update that I have had my controller back for a few weeks - it actually needed a new relay. The controller is now working great.

Jason at Arrow Springs had it fixed and back to me in record time & at a very reasonable cost. I was not about to take it apart and put it back together.

Thanks for all the input - I learned a lot
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