PID Settings | Proportional-Only Control

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⌚Timestamps:
00:00 - Intro
00:50 - A typical flow control loop
01:53 - Proportional-Only control
03:14 - Examples
05:41 - Offset in PID control
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In this video, we’re going to look at the effects of Proportional-only action on a flow control loop.
Proportional-only control is the simplest of the PID controller actions but is seldom used in industrial production processes.
The problem with P-Only control is something called Offset. In this video, we’re going to explain Offset and show you how and when it occurs.
The controller in our loop is typical of most controllers. We can adjust the setpoint and switch between auto and manual. In manual control, we can adjust the controller output to the exact amount we want.
Our flow loop has a pump to move our process fluid. We can turn the pump on or off which will be very helpful for observing PID responses in static and dynamic conditions.
Let’s start investigating the effects of adjusting the amount of Proportional action on our flow loop.
The controller output range is 4 to 20mA representing 0 to 100%. When the process is stable, the controller output will be at some value between 4 to 20mA.
The Process Variable is also represented by a 4 to 20mA signal from the Flow transmitter. This signal represents 0 to 100% of the process variable.
The controller’s job is to ensure that the Process Variable is the same as the Setpoint. The controller is always looking at the difference between the Setpoint and the Process Variable. This difference is often referred to as the Error.
Proportional Action is an Amplification of the Error. This Proportional amplification has no units and often is referred to as Gain. This amplified result is added to the current controller output.
We have a simple math formula:
New Controller output = Previous Controller output (CO) + (Gain × Error)
Let’s look at an example of Proportional Action and how that math formula applies.
We’ll start with the pump OFF. With the controller on Manual, we’ll set the output to 50%. We’ll set the Gain to 1.
We’ll set the controller to Auto. With the pump OFF, the PV or Process Variable will be 0.
The Setpoint change of 10% produced a 10% change in Controller output. Why? The Controller Output (CO) changed by 10% from 50% to 60%.
Because the Gain is 1, the proportional action will only add 10% to the controller output. The Controller output was at 50%, so adding the proportional response will move it to 60%.
With the Pump OFF, we have no possible change in the process variable therefore our Proportional Action is acting on a static condition.
Once the pump starts, we are in a dynamic environment and variables are changing with time.
We start with the Process Variable at the setpoint value of 75%.
When we introduce a setpoint change to 65%, the Controller initiates Proportional Action and attempts to change the Process Variable to move to 65%. But, the Process Variable only goes to 69% and stays there!
A proportional-only controller does the job expected of it, at least until a disturbance, process variable, or setpoint change happens.
A process disturbance will cause the process variable to change and the controller will act.
Unfortunately, the process will recover back to a condition of stability, BUT NOT with the process variable at the set point.
The difference between process variable and setpoint is called Offset and occurs in Proportional-Only Controllers.
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[@SEALTRONICS]

I don't know how to explain my anxiety and happiness when u post such awesome videos, please guys keep it up, love you, i want you to open a branch in Zimbabwe please, i will be the ambassador of RealPars in Zimbabwe 💞💞💞💞💞💞

[@realpars]

Thanks a lot for your kind comment and support, Amos! We're happy to hear that.

[@Diski76]

As always the land talks RealPars👌👌

[@hectorenriquesantandermeza5208]

Very Well Explained Real Pars! It will be awesome if in the future you can make a video related to Adaptive Control for Non-Linear Systems.

[@realpars]

Hi Hector, Thanks for your topic suggestion! I will pass it on to our course developers. Happy learning!

[@eugenepohjola258]

Howdy. Credits to RealPars for taking the time and effort to make these educational videos. As a curiosity. The European understanding of positive control is that the control output follows the set value. Increasing set point increases control output. Default in Siemens controllers. The American way of positive control is that the control output follows the process value. An increase in process value increases the contol output. Default in Omron controllers. Positive European: "Controlling of heating." Positive American: "Controlling of cooling." Regards.

[@realpars]

Thanks for your support, Eugene! We appreciate that

[@eugenepohjola258]

@@realpars Howdy. Sirs, Ma'ams. You are most kind to say so. Yeah. Back in my career days I remember almost gone nuts not getting the flippin' Omron to control. I only got it to bang-bang from rail to rail. So eventually I checked the manual and switched the direction. Voila'. Began to work like magic. Regards.

[@aircates]

I really appreciate these videos. I am a Master Toyota technician and what I find interesting is how much the automotive industry industry is incorporating some of these technologies into their systems. A case in point, is our direct injection engines which now use a brushless 3 phase fuel pump and fuel pressure transducers to monitor pressure. It is really not much of a stretch to understand the mechanics of PLC operation.

[@realpars]

Hi @aircates. Thanks for your comment. As you know, a car is loaded with computers. ECM's, ECU's....etc...etc..... And of course loaded with active sensors that detect everything from flow to pressure to temperature.....and much more!

[@aircates]

@@realpars absolutely correct!! I’m seriously considering changing professions from automotive to industrial troubleshooting. This is much more interesting to me and the way the systems interact is not unlike many automotive systems. In fact, some of the illustrations you use to explain some systems are automotive.

[@asadiqbal87]

thanks real pars another great video

[@realpars]

Glad you enjoyed it!

[@maryambayani568]

Well explained!

[@realpars]

Thank you, Maryam

[@mustaphaaitsidimou9177]

Really i appreciate these videos. Thank you very much

[@mustaphaaitsidimou9177]

In a control loop I found it already setting the P,I &D . But the measurement always exceeds the setpoint at 14% and then it returns stable. in this case it is necessary to act on P,I or D. Thank you for your response 😊

[@realpars]

You're very welcome!

[@aminokamad1681]

Awesome 🔥🔥🔥

[@realpars]

Thank you, Amino!

[@benhurley280]

Awesome 😎

[@realpars]

Thank you!

[@anatolyterpugov4627]

I understand correctly that at 4:39 the setpoint should change to 10, and not to 20, how is it with you?

[@realpars]

Hi @Anatoly Terpugov. You are correct. The value in the controller setting SP window should show 10 and not 20. The graph correctly shows that the SP is 10. Thanks for pointing that out!

[@s001b]

Thank you

[@realpars]

You're welcome!

[@montesdeocaf.2797]

Very good!!!

[@realpars]

Thank you!

[@vazgen6672]

Still great video as always

[@bitebonumbere1426]

@ 6:23: "In our next video..." Please don't fail to release this next video very soon. Thanks RealPars. 😊

[@realpars]

Thanks for your support, Bitebo!

[@shrikantsharma2321]

Please make video on siemens vfd starter software . Your videos are very helpful. Love from India.

[@realpars]

Hi Shrikant, Thanks for your comment! We have quite some video courses on VFD, feel free to check those out over here kzbin.info?search_query=+siemens+vfd+realpars Happy learning!

[@isakoqv]

Great way to gain some intuition! Maybe do a crash course on model predictive control when you're done with PID?

[@realpars]

Thanks for the topic suggestion! Great one, I will happily pass it on to our course developers. Happy learning and thanks for sharing!

[@mrtechie6810]

I want to add PID temperature control to my 240VAC instant hot water heater. What controller and sensor would you recommend? Is there such a thing as proportional heater control? A heater controller that factors in flow rate?

[@realpars]

Hi Mr Techie. Thanks for reaching out. I'm curious about why you want PID control for your hot water on-demand heater. I'm gonna go out on a limb here and suggest that an add-on PID control is not practical or easily accomplished. I don't know what vendor made your heater, but I assume it has a built-in controller already. Can you provide any additional info please?

[@mrtechie6810]

@@realpars It has manual switches for two heating elements: low, high (or both). Further adjustment is by manually adjusting the water flow rate. No electronic nor mechanical thermostatic control (except for a thermal safety cutoff in case of overheating). Atmor brand, model Super 900

[@mutiuadegboye3827]

Can you please tell me the software/tool you used to design your figure (figure at 1:50)?

[@realpars]

Hi Mutiu! Thanks for your comment! I am actually not sure about that as all our designs are created by our Graphic and Animation department.

[@alexcaceres3060]

💓

[@mohammadibrahim-om9qe]

Ia have a question please. I deal with PID level actuator, I put the set point (it's level controller). The problem is when tge the PV varies, the actuator goes to it's maximum output (fully closed or fully open) 0% to 100%. this leads to a big oscillating in flow rate, even when using a small gain, what can I do to get semi stable level and flow rate?

[@realpars]

Hi mohammed ibrahim. Thanks for contacting us. I can’t answer straight away as I don’t understand your loop quite yet. I’m not sure what your PV is. Are you measuring level or flow? Are you controlling level or flow? Is the flow rate you refer to a measure of the flow going through a pipe and into a tank where the level is being controlled? Is the flowrate a measure MV of a flow transmitter? I’ll keep an eye out for your replies.

[@hamdaniyusuf_dani]

I had some similar problems many years ago. It turned out that the cause is in control valve positioner's settings and pneumatic connections to the actuator. Can you control the opening of the control valve manually? Try to send 4 mA (0%) to the positioner, then increase it bit by bit, to 25%, 50%, 75% and 100%.

[@jbpilon02]

Hello, thank you for this video. I don't understand the formula CO=CO+(gain x error) because, after each scan, CO would augment to reach 100%. In a E5AR Omron controller, there is a parameter called manual reset which is a fixed value added to (gain x error). Then, the formula would be CO = (manual reset value)+(gain x error). So, even if the CO change depending on the error, the manual reset velue will always be at 50%. Am i correct ?

[@realpars]

Hi @jbpilon2. Thanks very much for your question. I’m not sure what you mean by “each scan” as an analog control loop is continuous. In any control loop, it is desirable that the controller output (CO) never reaches 100%, or 0% as the final actuator is at maximum or minimum. If that happens, the controller has no further effect on the PV. In a perfect world, let’s assume the CO is at 50% for a PV of 50%. We want to ensure that the Gain is not high enough to drive the CO to 100% or 0%. I’m not familiar with the E5AR Omron controller but I assume it is a temperature controller. I’d be interested in hearing more about the “manual reset value” that you describe. In most PID controllers, the term “reset” is another name for “Integral” or the “I” in PID. I’m looking forward to your response.

[@jbpilon02]

@@realpars Hello, interesting conversation. In math calculation, if i programmed the formula CO=CO+(gain x error), at each scan of the computer, CO will augment. I think we retreive a parameter like "manual reset value" in many controllers. It is a fixed value and it is used to manually remove the error when the process has reached his stability. When error=0, the output will continu to be activated with the manual reset value. In some controller, we also retreive the parameter "automatic reset" which is another name for the integral. So the formula could be CO=MRV + (gain x error). MRV = Manual reset value. Thank you again for the video. I wil use it in my courses. JB

[@kimaipet]

@@jbpilon02correct formula is CO = gain * error

[@jbpilon02]

@@kimaipet Hello, What's happen when the error=0 ? No command ? Even if the error=0, we need a command to maintain the temperature=set point. In a Proportionnal control loop, the manual reset value will do it. CO=MRV+(gain x error). So if error=0, CO=MRV.

[@kimaipet]

@@jbpilon02This is the main disadvantage of P controller. It always has offset error.

[@prasadadavi6618]

Hi, can you please help me understand the root cause of offset?

[@realpars]

Hi @Prasad Adavi. That's a tough question to answer quickly. In a nutshell, the controller's proportional action acts on the error signal and does its best to bring the PV back to SP. Unfortunately, after its' initial action, the PV does not reach the SP and no further action will occur. That's why Integral action is introduced. Integral action will continue to move the controller output until the PV does equal the SP and offset is eliminated.

[@clsullad]

Please make videos on omron plcs , Thank you

[@realpars]

Thanks for your topic suggestion, Chinnaraj! I will pass it on to our course developers. Happy learning!

[@clsullad]

@@realpars Thank you so much for your consideration , looking forward for Omron plc topics

[@mutugimaina7841]

How does simple water purifier machine operate. Explain each parts function .

[@realpars]

Thanks for your feedback and suggestions, Kennedy! I will happily pass this on to our course developers for possible future video courses. Happy learning!

[@mike-EE]

cant wait for the integral. the most difficult part

[@Korystuwatch42]

4:32 Are you sure there is no calculation mistake? Because if the SP is 20, and the PV is 0, we get an error of 20. Multiply it by the Gain of 2, and we get 40%. 50%+40% = 90?

[@realpars]

Hi there. You have a good eye. Thanks for reaching out. There is an error in the graphic. Please refer to 4:46. The SP window shows an SP of 20. The SP window should indicate 10, not 20. The video narrative states a SP change of 10. The Error value in the calculation is 10. If the SP was changed by 20, we would get an error of 20. And, if we multiplied by 20, we would indeed get an increase in output of 40%.

[@AlexandreSantos-gg9il]

Could you do a video on safety relay? from Brazil, thanks

[@realpars]

Thanks for the topic suggestion, Alexandre! Will happily pass it on to our course developers. Happy learning!

[@laithjawad9208]

This is FT200 flow transmitter not DP . Thanks

[@realpars]

Hi @laith jawad. Hey....thanks for your feedback! You are correct. FT200 is indeed a flow transmitter. At the same time, it is a differential pressure (DP) flow transmitter. The high and low ports of this DP flow transmitter are located on either side of an orifice plate.

[@enginerepairguy]

It sad as a student that you charge yearly for your pro subscribtion. Its amazing value but a bit steep as an student for a whole year 😔

[@realpars]

Thanks for your comment! We understand this price is not always doable for everyone. We do also offer a monthly subscription plan, which is €19,99 per month, but can be cancelled on a monthly basis. Luckily, we provide new video courses each week for free on our KZbin channel. Hopefully, you are able to join our course library soon!