PID Controller Explained
RealPars
https://www.youtube.com/watch?v=fv6dLTEvl74

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0:00 This video is brought to you by us, RealPars!
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0:10 Head on over to realpars.com and start learning now In this video, we're going to talk about the PID Controller
0:20 and its transformation from a single station device to what it has evolved into today.
0:27 We’re going to explain why PID Controllers are used in industrial processes instead of simple ON/OFF Controllers.
0:35 We’ll illustrate how Controller settings called Proportional, Integral and Derivative affect different processes under control.
0:43 We’ll also provide an overview of the very important activity called Controller Tuning. Let’s start with a discussion about home temperature control
0:52 as it’s familiar to lots of people. This house has a furnace that distributes heat throughout,
0:58 and a wall-mounted controller called a thermostat. The thermostat has a sensor that measures the house temperature
1:05 and compares that measurement to an adjustable setpoint. If the room temperature is below the setpoint, the furnace is turned ON.
1:14 When the room temperature increases above the setpoint, the furnace turns OFF. This type of control is referred to as ON/OFF or Bang-Bang Control.
1:25 Here’s a plot of what the room temperature does over a period of time as the furnace turns ON and OFF.
1:31 As you can see, the temperature is not exactly held at the setpoint of seventy degrees Fahrenheit,
1:36 but cycles above and below the setpoint. ON/OFF control may be ok for your house,
1:42 but it is not ok for industrial processes or motion control. Let’s look at an example of tank level control to explain why.
1:52 The Valve fills the tank as the pump drains it. If the valve is operated with ON/OFF control,
1:58 the water will fluctuate around the 50% setpoint. For our purpose, let’s say the fluctuation is plus or minus ten percent.
2:07 In most industrial applications, this fluctuation around the setpoint is not acceptable.
2:13 OK, well, what if it’s possible to throttle the valve and place it in any position between ON and OFF?
2:21 Now we can move on to talking about a PID Controller. P stands for Proportional, I stands for Integral, and D stands for Derivative.
2:32 Because every process responds differently, the PID controller determines how much and how quickly correction is applied
2:40 by using varying amounts of *Proportional, Integral, and Derivative* action. Each block contributes a unique signal
2:47 that is added together to create the controller output signal. Let’s look at how a PID Controller fits into a feedback control loop.
2:57 The Controller is responsible for ensuring that the Process remains as close to the desired value as possible regardless of various disruptions.
3:06 The controller ****compares the Transmitter Process Variable, or PV signal, and the Setpoint.
3:12 Based on that comparison, the controller produces an output signal to operate the Final Control Element.
3:19 This PID Controller output is capable of operating the Final Control Element over its entire 100% range.
3:28 Most modern PID Controllers are part of a PLC or DCS and are created in the program control logic using block commands.
3:38 Before PLCs came along, a PID controller was a stand-alone device responsible for controlling one loop.
3:47 A control room would have dozens or hundreds of stand-alone controllers mounted on a panel.
3:53 There are still many stand-alone PID controllers being manufactured and used today.
3:59 OK, let’s get back and talk about what each of the P, I, and D components of the PID controller does.
4:07 Remember earlier we said that the PID Controller is responsible for ensuring that the Process remains
4:13 as close to the setpoint as possible regardless of various disruptions. Let’s refer to the difference between the Process Variable
4:22 and the Setpoint as the Error signal. *The proportional block* creates an output signal proportional
4:29 to the magnitude of the Error Signal. Unfortunately, the closer you get to the setpoint, the less it pushes.
4:37 Eventually, the process just runs continuously close to the setpoint, but not quite there.
4:44 That’s when Integral jumps in. The *integral block* creates an output proportional
4:50 to the duration and magnitude of the Error Signal. The longer the error and the greater the amount, the larger the integral output.
4:59 As long as an Error exists, Integral action will continue. The *derivative block* creates an output signal proportional
5:08 to the rate of change of the error signal. The faster the error changes, the larger the derivative output.
5:16 Derivative control looks ahead to see what the error will be in the future and contributes to the controller output accordingly.
5:25 That brings us to a term called Controller Tuning. We said earlier that every process responds differently
5:33 and that the PID controller determines how much and how quickly correction is applied by adjusting *Proportional, Integral, and Derivative* action.
5:42 Controller Tuning involves correctly setting the controller P, I, and D values for specific process requirements.
5:51 Interestingly, the correct settings achieved by Controller Tuning can differ vastly between processes because of specific requirements.
6:01 For example, after the controller has been tuned, a setpoint bump of one percent in a tank level control
6:08 produces a quarter-wave damped response. This type of response may be suitable in a tank-level process
6:15 but could be disastrous in a motion control process. There are many different manual methods for tuning a controller
6:23 that involves observing the process response after inflicting controller setpoint changes.
6:29 One method involves increasing the amount of setpoint change and repeating the procedure
6:35 until the process enters a state of steady-state oscillation. This method of tuning produces adequate results
6:43 but is often impractical in many applications. For example, how practical is it to force the fluid level in a large tank
6:51 to reach a steady-state oscillation? Most process controllers, PLC, and DCS loop controllers sold today
6:59 have Autotuning capability. The PID controller learns how the process responds to a change in setpoint,
7:07 and suggested PID settings. Regardless of whether the initial PID parameters are derived
7:14 from manual or auto-tuning methods, additional tweaking is often required by seasoned automation professionals
7:21 to get the response desired. That should do it for this video.
7:25 If you want to learn more about PID control you might want to watch our other two videos called
7:31 *“What are PID Tuning Parameters?”* and *“How to Tune a PID Controller.”*
7:37 You can find the links to these videos in the description. Ok,… let's review:
7:43 An ON/OFF or Bang-Bang controller has only two output conditions and switches abruptly between these two conditions.
7:52 In a PID Controller, P stands for Proportional, I stands for Integral, and D stands for Derivative.
8:01 The PID Controller is responsible for ensuring that the Process remains as close to the desired value as possible regardless of various disruptions.
8:11 The PID controller determines how much and how quickly correction is applied by using varying amounts of P, I, and D action.
8:22 *The proportional block* creates an output signal proportional to the magnitude of the Error Signal.
8:28 The *integral block* creates an output proportional to the duration and magnitude of the Error Signal.
8:35 The *derivative block* creates an output signal proportional to the rate of change of the error signal.
8:41 Controller Tuning involves correctly setting the controller P, I, and D values for specific process requirements either manually or automatically.
8:54 Want to learn PLC programming in an easy-to-understand format? and take your career to the next level?
9:01 Head on over to realpars.com