Isothermal ripple

Dear Sir/Madam,

We are using a Eurotherm 3200 controller and we input a temperature profile with Labview. The reading from the Eurotherm's thermocouple shows that it follows the input profile but on isothermal stages it creates a 5C ripple every 8 minutes. Can you please help out? If you post an email I can send an *.xlsx file with the input/output data. Thank you in advance.
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  • Hi George,

    This looks like the control PID parameters are not tuned correctly to match the load you are trying to control the temperature. I am assuming you are changing the Setpoint on the controller via Labview and the ripple occurs when the temperature is stable.

    If you can start an autotune and let controller calculate the best PID parameters for your load.

    Regards
    Dimitris
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  • Hello Dimitri,

    Due to the nature of the application, I am sending to the controller a temperature point every minute, thus forming the temperature profile. In other words I input a waveform whose points are spaced at 1 minute apart. Obviously this is preventing the controller of calculating the needed values during the isothermal stage.

    Based on the temperature pattern that I am sending, is there a way to make the controller behave better during the isothermal stage?
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  • Hi George,
    You can still tune the controller to the load. Start from a known steady temperature T1, wait for the temperature to become stable. Start Autotune and Change the temperature to T2 and wait for the tuning to finish. T1 and T2 can be send via Labview.

    If autotuning is not possible then you will need to manually tune the controller to the load. For this change the PID values (one at a time) and observe the effect on the ripple. Record the PID values before and after so you revert back if you need.

    How big is the difference in temperature you write via Labview every minute?
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