Plain aluminium is off by 50% or more. Same with heatsinks. It's
almost impossible to measure with an optical thermometer or thermal
imager.
To get around this put a piece of plain white office paper on it.
I did tests with a thermocouple probe and a heatsink and the most
accurate results are achieved by simply sticking a plain white paper
sticker on. Of course the glue doesn't stand the temperature so it's
no good to use a sticker on the hotplate.
Generally optical thermometers are problematic. At least you noticed
the problem, I know plenty of people who just accept the reading at
face value and think they do precision work when indeed all they do is
waste time and space.
It is easier to get precise values with a thermocouple. I drilled a
hole in the edge of my hotplate to hold the thermocouple.
ST
On Fri, Jul 9, 2010 at 4:56 AM, 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?
>
>