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
    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:

    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
    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
    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:
    My input power requirement is less than 10W and the temperature range we need to control is between 15 degree to 45 degree.
  4. kobyyu

    Thread Starter New Member

    Mar 29, 2006
    anyone can help me???
  5. n9352527

    AAC Fanatic!

    Oct 14, 2005
    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


    Feb 24, 2006
    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
    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:
    AD595 Monolithic Thermocouple Amp

    It will work stand-alone with good accuracy from 10 to 50 ˚ celcius. No thermocouple required in that range.

    Ebay has them for ten or fifteen bucks a pop.

    A driver for the peltier will be required. (See figures 9 and 13 in the datasheet.)