A pitch for PID controllers for fans

I was wondering if a PID controller could be used to control a fan to help an overfire condition. A PID controller not only monitors the current temp, but is constantly calculating with a computer chip the rate of change of the temp, and through that calculation, it controls when a device (like a fan or a heater, or both) turns on or off depending on various parameters such as rate of change and the difference between the current temp and the desired set value. You tell the device how you want it to behave with several input values. Has anyone tried to program one to turn on a fan even before a set point is reached if the temperature rises fast enough.

I'm using one not for a fan, but as an overtemp alarm because it was the cheapest way I found to get an alarm at these temperatures. Overkill for just a monitor/alarm, but I'm thinking that it could work as a fan controller to help prevent overfiring,too.

This thread a while back discusses the use of a PID for an alarm: http://www.hearth.com/talk/threads/digital-led-temp-readout-and-alarm-installed.76244/#post-965780 I got my stuff on ebay. One of these: http://www.ebay.com/itm/PID-Digital...614?pt=LH_DefaultDomain_0&hash=item337ab454b6 It comes with a k thermocouple. This one is somewhat limited in it's features, but there are others for a bit more. I noticed in particular that mine doesn't have an actual alarm; you have to use the controller relay for that, which is okay, but it would be nice to have both.

BTW, here is a cheap alarm beeper and light that operates on 120 VAC, which makes it very easy to wire in to the PID relay output: http://www.ebay.com/itm/110V-AC-22m...577?pt=LH_DefaultDomain_0&hash=item19cae87dc1 It works fine for me and I just taped it to the controller.

In any case, these things can be a pretty cheap way to monitor temps and set an alarm and even turn on a fan at a certain temperature.