Thermocouple tutorial

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StigOfTheDump

Senior Member
I am planning a reflow toaster oven and bought some cheap thermocouples. After a days research I found that the proper way to use them is with a MAX6675 chip which seems to be obsolete or a MAX31855 which I can't find in UK. Other methods used AD595AQ which seem to be about 5 times the price of my thermocouples.

I found this tutorial which explained thermocuples very clearly, and thought other people might enjoy it. It is a 30 min video.

http://www.eevblog.com/2013/02/03/eevblog-419-thermocouple-tutorial/

I am now thinking that I can use op amps on my thermocouples and if I keep the cold junctions closely (and thermally) grouped I could use the DS18B20 for my cold junction reference and use either lookup tables or some math(s) for the compensation.

Any comments?
 
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StigOfTheDump

Senior Member
Thanks. The first link is a tempting price but in China. All UK suppliers are at a price that doesn't fit within my budget.

Many years ago I had a bad experience importing something that makes me very reluctant to try it again.

I bought Netscape 4.7 browser on CD from the US for about £4. When it arrived at the door I had to pay the VAT (less than £1, which I could reclaim, as I was VAT registered) plus a £10 handling fee to the shipping agent that processed it, which I could not recover. This tripled the price of my item.
 
JimPerry

JimPerry

Senior Member
Never had to pay extra for Ebay stuff in years - most is marked as Gift and only a few dollars value - so exempt :rolleyes:
 
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StigOfTheDump

Senior Member
Thanks for that I will give it a good read when my toaster cools down enough to move from in front of the monitor.

Important search lesson learned here. "thermocouple" didn't find your thread, but "thermocouple*" did. I had always assumed it would find anything containing the searched text not just the exact word.
 
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Billo

Senior Member
Imports into the UK under 15GBP are not charged any duty or taxes. No electronic components or PCB should be charged duty. Over 15GBP, taxes will be assessed and a processing fee added.

If it is under 15GBP just have it sent in by mail (not courier) and everything should be okay.

I have sent lots of small electronic items to the UK and never had any problems. Only once was tax and processing charged , as the total was over the 15 quid.
 
Buzby

Buzby

Senior Member
Billo said:
Imports into the UK under 15GBP are not charged any duty or taxes ....
Click to expand...
Correct, but the £15 includes the cost of the postage.

I wanted a $10 chip, but the seller insisted on some postage method that brought the total into the chargeable zone. I talked him into a cheaper one.
Another case was some low cost but bulky items from the US, again the postage took the total over the limit.
 
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Paix

Senior Member
I bought a Balun book from a well know ferrite component manufacturer in the US. they described it as "Electronic Components", was over the limit, so attracted VAT and £8 handling charge by Royal Mail. It did take the shine off the purchase a little. A has been mentioned adding the postage to the value of the item just rubs salt into the wound.

I like Free Economy China Post and Pound shops because they leave you knowing where you are. :)
 
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Puuhaaja

Senior Member
Thanks for sharing this tutorial. At the moment I'm making my own ultimaker 3d printer which would cost 1700€ but because I'm ordering suitable parts all over the world the price will be about 300€. Next problem will be thermocoupleboard which is using ad597 chip. The problem is that a mere chip cost about 10€. I don't know well how thermocouples are working but I had planned if I could do it by using other chip etc...

https://www.ultimaker.com/products/heater-cartridge
https://www.ultimaker.com/products/thermocouple-transmitter

Anyways the parts above would cost about 60€ which is quite much and I will do my own version of those set which will cost about 10-15€.
 
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