High-Temperature thermometer - any ideas?

[presario1425]

I've got one of those convection ovens at home where you rotate the dial to set the temperature. Well, the dial has become loose and the markings are fading away. I could easily buy a replacement dial (or ... a whole new oven for that matter) and not have all my cakes come out as charcoal

But why take the easy route when I can design a digital thermometer, right? I was thinking of using a k-type thermocouple, an amplifier IC, a PIC and a 3-digit 7-segment LED module. I need to measure upto 450F. I can easily find the last two components, but searching for a low-noise amplifier (since the k-type's temp coefficient is only about 41 uV/ deg. C) and an inexpensive k-type thermocouple has not proven fruitful so far. I don't want to use those expensive ICs specially built for the k-type thermocouples (where's the fun in that?).

Any idea which low-noise voltage amplifier ICs I can look at and more importantly, any idea where I can buy those k-type thermocouples for less than $10 (if at all possible)? Thanks in advance for any help.

[mackrackit]

Hi,

I am using a LM358 with a "K" type thermocouple and a LM34 for reference temperature.

I get the thermocouples from omega.com.
http://www.omega.com/ppt/pptsc.asp?r...TXL&Nav=tema07
Is the one I am using but these are nice and in your price range
http://www.omega.com/pptst/WT.html

But if 450 is all the higher you need, a "K" is overkill "T" will go up to 752F and one of the leads is copper. This helps with reference connection problems.

When you pick your PIC, get one with a 10 bit ADC and enough program memory for the look-up tables.

[Luciano]

Hi,

Oven Thermometer:
http://www.chefscatalog.com/product/...ermometer.aspx

No batteries.

Ready for the Christmas cookies 2007!

Best regards,

Luciano

[mackrackit]

Whats the round dial and needle?....Is that analog???

[presario1425]

Hi,

I am using a LM358 with a "K" type thermocouple and a LM34 for reference temperature.

I get the thermocouples from omega.com.
http://www.omega.com/ppt/pptsc.asp?r...TXL&Nav=tema07
Is the one I am using but these are nice and in your price range
http://www.omega.com/pptst/WT.html

But if 450 is all the higher you need, a "K" is overkill "T" will go up to 752F and one of the leads is copper. This helps with reference connection problems.

When you pick your PIC, get one with a 10 bit ADC and enough program memory for the look-up tables.

Great info mackrackit ... exactly what I was looking for. Thanks!

Hi,

Oven Thermometer:
http://www.chefscatalog.com/product/...ermometer.aspx

No batteries.

Ready for the Christmas cookies 2007!

Best regards,

Luciano

Luciano, thanks for the info, but where's the fun in that?

[mister_e]

the fun is how you'll interface it to your PIC

[Luciano]

Luciano, thanks for the info, but where's the fun in that?

The fun? The Christmas cookies won't be postponed to 2008 or 2009!

* * *

See the links in the last post of this thread:
http://www.picbasic.co.uk/forum/showthread.php?t=3416
(Circuitcellar PDF file, Build an SMT Reflow Oven Controller).


Best regards,

Luciano

[tenaja]

Luciano, for reference, you can copy the link to the number in the dark blue bar of the thread to link straight to a specific post. For instance, in your example, use this:

http://www.picbasic.co.uk/forum/show...7&postcount=13

And you'll see that the 13 is the number corresponding to the post you referenced.


And for what it's worth, most toaster ovens are too inconsistent for anything but very small boards, if you have any concern whatsoever about overheating your components. The temperature at various positions in the oven varies a huge amount. You'll find that components by the door will have not flowed yet, but components in the middle are getting fried. A small fan to slowly move the air around will greatly improve it.

[Luciano]

Hi,

This thread is about a thermometer for an oven.
No SMD involved, just cookies and chickens!

In the Circuit Cellar article they use an AD595 monolithic
thermocouple amplifier which could be used for this project.

Best regards,

Luciano