# help needed for Temperature controller design

Discussion in 'The Projects Forum' started by kobyyu, Mar 29, 2006.

1. ### kobyyu Thread Starter New Member

Mar 29, 2006
3
0
I'm currently desining a temperature controller, which controls the temperature of the aluminium block on the peltier device. I will use the sensor AD590, which is attached on the peltier device, to measure the temperature of the aluminium block. I'm told to design a PID controller. I got a circuit diagram for a similar design: http://newton.ex.ac.uk/teaching/CDHW/Feedback/DIY-PID.html.

Anyone can help me how I can approach the project???

I'm currently trying to find the transfer function of the peltier device, which then i can find out the transfer function for my contorller. Is this a good approach?

Thanks...I really need you guys help!!!

2. ### windoze killa AAC Fanatic!

Feb 23, 2006
605
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Can you get datasheets for the peltier device? If we knew what the input requirements were we could better help you with the design.

3. ### kobyyu Thread Starter New Member

Mar 29, 2006
3
0
I don't have a datasheet for the peltier device, and in fact i couldn't get one from the Internet either. What I got for the peltier device is the link following: http://www.peltier-info.com/info.html
My input power requirement is less than 10W and the temperature range we need to control is between 15 degree to 45 degree.
Thanks!

4. ### kobyyu Thread Starter New Member

Mar 29, 2006
3
0
anyone can help me???

5. ### n9352527 AAC Fanatic!

Oct 14, 2005
1,198
4
Why don't you start by checking out wether the peltier is able to cool down the block under the required extremes? For example at maximum peltier power and maximum air temperature is minimum block temperature achievable?

Then, you could find the power loss of the system under a constant air temperature. Put a constant power to the peltier to maintain a constant temperature and just calculate the system loss for delta temperature.

You could also obtain the lag of the system, i.e. the rise of the temperature at certain point on the block against peltier power increase.

Then, you could find the cooling characteristics of the block. This involves measuring the decreasing temperature of the block at intervals while it is cooling off from a certain temperature.

I believe once you obtained these details, you would able to reasonably derive the PID coefficients and then fine tune them later.

Is this a project or an academic exercise and how tight do you want the temperature to be? For a project, I, personally, would not bother with transfer function and would go straight to controller adjustments.

6. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
In fact the main reason that PID loops are so successful is they they are used in situations where the transfer function of the "plant" is unknown or difficult to determine.

7. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
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I don't know what peltiers will or won't do, but I've built a couple setpoint controllers.

This little gem worked well for me: