Additional Tunning in Controllers

Hi, Francis,

If you're going to get a reasonable answer to this, you'll need to be a lot more specific. There are, literally, thousands of different devices around that could be classed as controllers. Please spell out what you need to know.

Also, please register.

Regards, John.

Dear John,

Thanks for your prompt.

As I know, PID Controller is having Kp, Ti, Td are the parameters to be tuned. Any other parameter else for additional tuning in these controller.

Thanks and Regards,

Francis

PID controllers typically have only the three adjustments you mentionned. Kp is the gain control, normally labeled Proportional Band, where 100% is a gain of 1, 10% is a gain of 10. Ti is the integral mode, normally labeled as Reset, and Td is the rate or derivitive mode, normally labeled as Derivative time.

Some PID controllers have a self-tuning mode. You need the manual to explain how to use this function without letting the process get into an unsafe operating condition during the learning process.

Most flow and pressure loops typically have capacity, but essentially no dead time, and are controlled with only the P & I modes. Loops with dead time, like temperature loops or those with a transport delay of the feedstock require the Derivative mode.

There is an extensive body of literature on how to tune loops. Is that what you are looking for?

Dear John/DaveR

Quite clear your response about tuning of PID. Can you make me know about Self tuning and Auto tuning of the controller. Is it related to normal PID tuning or special(Addtional) tuning.

Thanks and Regards,

Francis

The self-tuning is an algorithm to set optimum values of the P, I and D functions of the controller. There is typically a learning mode procedure which has the ability for you to abort it if the process becomes unstable. This might occur for a very nonlinear process.

The problem Gigaconcept refers to on startup, or regularly for a batch process, was a concern on older (mostly analog) controllers. It was caused by the integral mode continually adding to the output until the controller reached the setpoint and causing a large overshoot until it stabilized. It should not be a problem with more modern controllers.

The Wikipedia entry gives quite a good explanation, and has some good links.

To an extent, any 'extra parameters' added (deadband etc.) will be dependent on what you're controlling - i.e. motor speed, temperature, pressure or whatever. Unless you're making your own controller (i.e. writing the code to drive 'something' using a PID algorithm), any extra parameters will already be dictated by the controller manufacturer - refer to their literature.

Again, I must point out that you haven't really given enough in your question.

Regards, John.

These http://www.cal-controls.com/ have quite a few extra parameters.

For example the ramp rate is useful at power on to reduce overshoot and have the PID tuned at setpoint.

Francis

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