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Desirable Features in PID Controller (Function Block)

12/03/2017 5:10 AM

Dear CR4 members,

I am developing a PID programming block to be used in PLC/ ESD/ PAC controllers. Currently I have completed basic functionality testing and would like to add some new features that will help the process/ system performance optimization. What in your experience and opinion, are the most desirable features/ functions lacking in current PID controllers.

Thanks.

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#1

Re: Desirable Features in PID Controller (Function block)

12/03/2017 9:09 AM

An application that was capable of calculating the Routh-Hurwitz stability equations would certainly be useful. This way one could easily calculate what can and cannot be done with a system.

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#2
In reply to #1

Re: Desirable Features in PID Controller (Function block)

12/03/2017 10:59 AM

That's a good idea. It will certainly be useful for Robotics and small scale R&D projects.

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#7
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Re: Desirable Features in PID Controller (Function block)

12/06/2017 10:38 AM

Couldn't that be on a CD or thumb-drive supplied with the PID controller?

I would like to see knobs on the thing, instead of having to hold down buttons for the precise quantity of time to get to the menu, much less affect tuning.

OR at least supply one or two pull-out knobs with the thing that would be inserted into recessed connection to set up the loop tuning. I like knobs.

Alternatively, have a mini-USB to a cellphone as the interface, and have the software load an app to the cellphone to enable loop tuning and set-up.

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#9
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Re: Desirable Features in PID Controller (Function block)

12/07/2017 2:20 AM

It will be coded inside the PID function block as a feature. It is not a stand-alone PID controller but library add-on for PAC/DCS/PLC application development software.

All the features will be accessible to operators via HMI workstation.

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#10
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Re: Desirable Features in PID Controller (Function block)

12/07/2017 8:51 AM

Now I see a problem. One of the things a controls engineer should learn about the Routh-Hurwitz theory is that one can change the PID settings so the system will destroy itself. Be very careful how much fredom you give a user that knows nothing.

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#11
In reply to #10

Re: Desirable Features in PID Controller (Function block)

12/07/2017 9:10 AM

yes, give the robot the freedom to self-destruct 10 seconds after transmitting this message...MI reboot.

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#12
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Re: Desirable Features in PID Controller (Function block)

12/08/2017 4:54 AM

Totally agree for the valid concern. In theory, each big company (Oil & Gas to be specific) hire Process tuning specialist during commissioning to study and tune different systems/ process loops. In practice, however, I have seen on some sites, people who just play guessing and put random gains. Luckily, all the PID blocks during commissioning are in offline-tracking mode so they can not do much damage.

I remember, how tricky and challenging it was during my graduate studies to understand and control the system where we had to draw root locus, nyquist plot, bode etc. , to study and to tune by using passive elements (resistors, capacitors etc). It was truly a proud feeling once you achieve optimum performance.

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#13
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Re: Desirable Features in PID Controller (Function block)

12/08/2017 9:17 AM

You've inadvertently touched on the crux of the entire "tuning" problem. Fidgety fingers will change settings. Most fidgety fingers aren't looking to optimize. They want to see what "this" does. Those who wish to optimize (like a Sheldon Cooper) believe they know better when they actually don't know enough.

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#14
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Re: Desirable Features in PID Controller (Function block)

12/13/2017 8:10 PM

I don't consider this an "off-topic" response. The original question was "what features would you add to a PID?" I like knobs more than buttons as well. This is good feedback to the original poster.

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#3

Re: Desirable Features in PID Controller (Function Block)

12/03/2017 11:44 AM
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#5
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Re: Desirable Features in PID Controller (Function Block)

12/04/2017 3:52 AM

Thanks Rixter. Auto-tuning has already been implemented and tested. It is working well. It can be made more precise and robust though by use of Discrete Fourier but will do it for next revision.

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#8
In reply to #3

Re: Desirable Features in PID Controller (Function Block)

12/06/2017 10:39 AM

You guys keep taking all the fun out of things. Kill joys!

I want knobs. Big knobs.

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#4

Re: Desirable Features in PID Controller (Function Block)

12/03/2017 12:50 PM
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#6

Re: Desirable Features in PID Controller (Function Block)

12/04/2017 10:59 AM

Time based set points and rate of change adjustments are really valuable for heat treating type operations or in flow rate controls. For heat treating, start with x degrees per time base rise followed by hold at temp followed by another controlled change rate followed by timed hold, continue for however many changes and holds needed. I have a glassblower friend who also uses such controls. The option to select either PWM (pulse width modulation) or proportional control would also be a great feature. PWM would likely be most reasonable for DC control and proportional for AC control.

I could also see links in the software to provide frequency output control, if you were driving a blower or pump with 3 phase AC and an error level output that could potentially drive a servo motor to mechanically balance a system, such as a throttle valve control.

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