jsurgeson Posted October 16, 2010 Share Posted October 16, 2010 I know this is partly a electronic design issue but I am sure that there are many here that are knowledgeable or have experience with regards digital temp indicators or controllers on forges. I have built a type k temp indicator for my 2 burner blown forge, here is the thing, when the forges get up to 600+ deg C the reading starts to jump around 600 - 1200 erratically different values. I thought this was a electronic issue however when I turned the burners and blower off, the reading immediately stabilized and slowly started to drop as it cooled. I assume from that, that it is not the electronics or the tc. Also when I tested outside of the forge, using a gas torch to apply heat directly to the tc, it remained stable all the way up to 800 odd degrees, the hottest i could get it with this little torch. What do you guys think? Quote Link to comment Share on other sites More sharing options...
youngdylan Posted October 16, 2010 Share Posted October 16, 2010 . I have built a type k temp indicator for my 2 burner blown forge, here is the thing, when the forges get up to 600+ deg C the reading starts to jump around 600 - 1200 erratically different values. I seem to recall K types suffer from one of the elements going none magnetic around the curie point which is somewhere around the 600 mark and this affects the output voltage. This might be related to what you're seeing. I'm sure type N don't have this issue Quote Link to comment Share on other sites More sharing options...
pkrankow Posted October 16, 2010 Share Posted October 16, 2010 I think the probe has a short in it. The curie point is down around 354C (I looked it up). I also looked up a chart of millivolt outputs, and 600C to 1200C is approximately doubling the output. Been a while since I played with thermocouples, and I am not an expert. Phil Quote Link to comment Share on other sites More sharing options...
jsurgeson Posted October 16, 2010 Author Share Posted October 16, 2010 The tc is brand new and as I said out of the forge with torch flame applied directly to the tc the reading is correct and stable well over 850 deg C Quote Link to comment Share on other sites More sharing options...
MattBower Posted October 16, 2010 Share Posted October 16, 2010 My guess is that whatever the problem is, it's related to the turbulence caused by the burners. (Turbulence that isn't a present out of the forge, in a torch flame.) You might try rigging up some kind of shield to help protect the probe, and see if that makes a difference. Quote Link to comment Share on other sites More sharing options...
jsurgeson Posted October 16, 2010 Author Share Posted October 16, 2010 Kinda of what I thought, just did not think that flame/air movement would cause the tc input to vary that much. I think I need to rig it so i can put a meter in the box to see if the tc output is actually changing as much as that. And a shield as you suggest might be a answer, do you know if commercial tc's are shielded from the turbulence or not? Quote Link to comment Share on other sites More sharing options...
MattBower Posted October 17, 2010 Share Posted October 17, 2010 Thermocouple protection tubes are commonly available, so I assume they're commonly used. Quote Link to comment Share on other sites More sharing options...
jsurgeson Posted October 17, 2010 Author Share Posted October 17, 2010 Do you know if protection tubes are designed for the turbulence issue or to protect it from damage, both? Quote Link to comment Share on other sites More sharing options...
Mainely,Bob Posted October 17, 2010 Share Posted October 17, 2010 Both,plus they make replacement while under power much easier. Quote Link to comment Share on other sites More sharing options...
Sweany Posted October 18, 2010 Share Posted October 18, 2010 http://www.coleparmer.com/catalog/product_view.asp?sku=9043386&pfx= just an SS tube with a plugged end really Quote Link to comment Share on other sites More sharing options...
MattBower Posted October 18, 2010 Share Posted October 18, 2010 http://www.coleparmer.com/catalog/product_view.asp?sku=9043386&pfx= just an SS tube with a plugged end really Yep. Depending on the temps you'll be running, ceramic might be better than stainless. (Even good stainless will scale away at high forging temps.) Quote Link to comment Share on other sites More sharing options...
jsurgeson Posted October 18, 2010 Author Share Posted October 18, 2010 SS tube, great idea thanks, even if it destructs after a while probably still cheaper than buying purpose made. Thanks for suggestions guys Quote Link to comment Share on other sites More sharing options...
Fosterob Posted October 18, 2010 Share Posted October 18, 2010 Use the SS to test your forge to see if it works and when it goes away then buy the good ceramic. Rob Quote Link to comment Share on other sites More sharing options...
jsurgeson Posted October 19, 2010 Author Share Posted October 19, 2010 Makes sense, however priced a 50mm one yesterday and found that they cost more than a complete type k tc with leads and fittings. Going to have to find another supplier or a cheaper solution. I am also going to try pulling the tc back into the tube in the wall, and see if thats does the trick. Quote Link to comment Share on other sites More sharing options...
MattBower Posted October 19, 2010 Share Posted October 19, 2010 Makes sense, however priced a 50mm one yesterday and found that they cost more than a complete type k tc with leads and fittings. I realize you're in a different country, but keep looking. I have to believe it must be possible to find a small ceramic tube for a reasonable price somewhere in South Africa. Quote Link to comment Share on other sites More sharing options...
jsurgeson Posted October 19, 2010 Author Share Posted October 19, 2010 Yeah there must be, unfortunately most of the companies and industry that uses refractory materials are the other side of the country. But I am sure I will come right. B) Quote Link to comment Share on other sites More sharing options...
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