Homebrew PCBs

I have an IR thermometer and experience the same thing.

I believe this is related to the concept of 'black body radiation'. The IR
thermometer is calibrated to measure the radiation of a pure black object
(absorbs light). If it's not pure black, then it will give a false reading.

That's my vague understanding, try googling 'black body radiation'.

If you use a thermocouple you won't have this problem! Or you can try
putting a black object on the hotplate, and measuring the temp of that.

On Fri, Jul 9, 2010 at 12:56 PM, rlspell2000 <rls@...>wrote:

>
>
> Bought a GOOD lab hot plate to do solder reflow. Half inch thick aluminum
> top, temp setting dial.
>
> When I first fired it up I very carefully found the settings on the dial
> that corresponded to 160C and 230C, the two temps I was interested in, for
> Toner Transfer, and for solder paste reflow.
>
> The IR thermometer said the dial was WAY off. By a factor of like 1.5.
> But this is OK, I just marked the spots on the dial and went about my
> business.
>
> Just did some toner transfer with the plate on the bottom and the normal
> iron on the top. I.E, the board and paper sandwiched between the hot plate
> and the iron. Set the hot plate for where the IR thermometer had found the
> setting for 160C
>
> After being on the hot plate for like 15 seconds the paper started to
> turn brown and smoke.
>
> WTF?
>
> I took the temp again. Yep, says right at 160C. But paper doesn't burn
> at that low a temp... ????
>
> I turned it down to the setting on the dial for 160, and tried again.
>
> I after it had cooled off I put a piece of paper on top of the hot plate
> and took *it's* temperature. Just about exactly 160C.
>
> After cleaning the board up and scraping off the burnt paper I ran it
> through again and it worked fine a the dial setting of 160C.
>
> Odd, no? IR non-emission coating on the plate or something?
>
>


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