Double PID for Temp Control

[John]

#3544

Hi,

Just received the unit, great design!

I am trying to control the temperature of a watercooled heatsink for a cpu to go through a test profile (-5 to 105 degree C) using a 400W flat sheet heater and a 400W (TEC) peltier device.
Heater and TEC are sandwhiched between the cpu contact plate and a watercooled block (constant water flow 15 degree c).

I could use a single PID loop to output to heater for heating up and TEC for cool down.
Since the TEC can both do the cooling and heating up by switching polarity; are there any advantage in using two PID loops.

All comments are welcomed.

John

[Brett]

#3781

Hi John, using 2 pid loops would ensure that you were getting the most precise control possible, as the best tuning parameters for heating may be different than the best tuning parameters for cooling. that being said, having 2 separate pid controllers makes it likely that they will fight eachother.

the common industrial solution is to use what is known as a “split range controller.” in this scenario, one pid controller is used, but if the output is <50%, the signal is sent to the cooling system, and if it's above 50% it's sent to the heating system. most split-range controllers also provision for a different set of tuning parameters for heating vs cooling.

this isn’t currently supported by the osPID, but all the pieces are there for a nice hack.

[dchris01]

#3782

I have made my IR reballing reflow station I am using osPID to control the top heater and also using a Rex-c100 PID to control the bottom. I am unable to get a stable preheat as the Rex-c100 is a bad cheap controller. I have been told that I can run the bottom and top separately using just the osPID can this be done with my machine. Bottom preheater is running 4 ceramic IR plates each is 400w and connected to Fotek SSR -25 DA and then to Rex-c100 PID. The top has 1 IR plate 250w also connected to another Fotek SSR -25 Da and this is connected to ospid. Can a profile be run from osPID to controll the two different heats. His is a picture of my machine it’s not much to look at but it’s working. With only problems with bottom preheat. How if it can be done will it connect or wired.http://img694.imageshack.us/i/imagecfp.jpg/

[christysinha]

#3783

You can use infrared water heaters in which you can easily control temperature. As name indicates infrared heaters uses infrared rays to make the water warm. It is cost effective as it does not use any fuel or electricity.

http://www.ceramicx.com/en/

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