Dimensioning of hot plate and heater cartridge

[Javier]

Hello all,

does someone have a reference for the dimensioning of a hot plate and heater cartridge system? I'm thinking along the lines of an application note that explains, give a hot plate of so and so square cms and a cartridge of so and so Watts then it takes so many seconds to reach Temperature X.

I couldn't find such an analysis anywhere and the approach "drill a hole in an aluminium block and hope for the better" stresses me a little bit.

Cheers and many thanks in advance

[Pjotr]

Hi Javier,

Currently I am working on a small hotplate for small SMD boards myself. The plate itself acts as a large thermal capacitor (>= 1K equivalent Farads if you can say so) fed with a thermal current (power). Which gives an almost linear rising temperature over time if not controlled, according to the following formula:

thermal_mass X temperature rise = power x time

Where thermal mass = specific heat X mass

In parallel to the thermal mass there is the heat loss to the surrounding which acts as a thermal resistance in parallel to the thermal capacitor. This resistance is mostly relatively large for a hotplate, 0.5 degK/W to 5 degK/W or so.

Here is a good explanation of the thermal metrics you are looking for: http://www.turk-hillinger.us/fileadmin/media/pdfs/berechnungsgrundlagen.pdf

It is in German but hopefully you get some understanding. It also shows graphs of maximum play of cartridge heaters related to the surface load (watts/cm2) of the cartridges.