Using 'CON_C' in TIA 17

You are attempting to achieve a bumpless transition from auto -> manual -> auto if I understand correctly.

Have you read the PID help details as well as looked inside the PID DB's comments for all the tags to see if there is a bumpless transition tag available that allows the PID block to automatically transfer the current setpoint to the next phase's setpoint automatically?

Not every PID controller out there provides this option.

If your specific PID block does not offer it, you can do an online search on how to perform PID mode transitions bumplessly and then write the required PLC logic to make it happen.

It is not complicated but does require some thought to get it right for every situation.

Francely

Hi everyone, I hope you are all doing well.

I am currently using the PID 'CONT_C' for flow control through a valve, and it works well in automatic mode.

The issue arises when switching from automatic to manual mode, and then back to automatic mode. The PID takes the actuator to 0%, closing the valve and I don´t know want it.

Could you please help me? It is critical for the process that this valve close, as we are dealing with large flow rates.

I have programmed the PID in OB30,  the setpoint (SP) for automatic mode in l/s, and the control action is in %. I have the proportional and integral values ​​configurable for manual mode, and the PID operates well in automatic mode.

I've checked some forums where similar issues occurred with the Compact PID, but I couldn't find a solution for the 'CONT_C'.

Thank you very much!

Read the F1-Help on the CONT_C PID block.

In "How CONT_C works" -> "Manual value processing" section, it states half your problem is automatically solved:

TIA Portal F1-Help

Changeover to automatic [from manual] mode is therefore bumpless.

That means virtually all you need is to do is:
While in Auto mode: Adjust the manual setpoint to be whatever the automatic mode setpoint currently is.

In the CONT_C_DB, that is MAN (manual value) for the input that needs to be revised every time the PID calculates a new value while in automatic mode.

You can review the parameters like PV, PV_PER, LMN, and LMN_PER to see which one is appropriate as the source value.

NOTE: you may need to scale the internal setpoint from automatic mode to match the manual input scaling (%, scaled like raw analog inputs, scaled engineering units)

You will need to review the CONT_C parameters in your DB live to see what value in automatic mode represents the equivalent of setpoint used to directly affect the output control device.

Once you find that, "DB####".<parameter>, you can do any scaling required to map it onto the manual input.

The HMI Manual input should be disabled while the PID is in automatic mode - unless you want a bumpy transition - which is what I think you are trying to avoid.

Francely

Okay, i mean, mm, currently in the 'MAN' parameter I have the manual SP value of the opening percentage that is entered from the HMI to manipulate the valve (0-100%).

As I understand it, in that parameter I should have the real value of the valve opening? That is, the PV? and not the value of SP...?

Thank you very much for your attention.