PID is an acronym for Proportional, Integral, and Derivative.
A PID controller is a device that is used to control a process.
The controller can be a physical, stand-alone device or a control block found in a PLC function database.
The PID portion of the controller
is a series of numbers that are used as adjustments in order to achieve your objective.
before we get started on today's video
if you love our videos, be sure to click the like button below.
then make sure to click subscribe
and the little bell to receive notifications of new RealPars videos.
This way you never miss another one!
A very simple example of a PID controller
would be the regulation of a heating and air conditioning system in a home.
Although there is a lot more to the controller than this example,
this will give you a basic idea of the purpose of a device like this.
Say you have the temperature in your home set to 70 degrees Fahrenheit.
This setting would be called the Setpoint or “SP” for short.
The current reading from the thermostat is 68 degrees.
This term is the Process Variable or “PV”.
The heating or cooling unit is the Control Variable or “CV”.
The Control Variable may also be referred to as the Manipulated Variable or “MV”.
There are different types of control action and for the temperature control in the house,
the controller action is a direct acting device meaning that the calculations are Setpoint minus Process Variable.
In our house example, we have a Set Point of 70 and the Process Variable is 68.
For this control when we subtract the Process Variable from the Set Point
we see that we have a value of 2.
This result is called the Error or “E” in our process.
In the simplest terms, our house is too cool and the controller tells the heating unit to turn on.
Remember, we are trying to get to 70 degrees.
The unit will remain ON until the Error in our process becomes zero.
Now let’s say that someone opens a window in the house and it’s very cold outside.
This disruption in the process is called Disturbance.
The factors in this process control may be “how fast do we want the temperature to reach the setpoint”
and “what could disturb our process?”
Clearly, there are many factors that can impact our processes
and adjusting our controller’s parameters is how we deal with those factors.
Another example of a slightly more complicated controlled process,
for understanding purposes, would be you changing lanes while driving.
You would be the controller, the lane that you want to be in is your Set Point,
the steering wheel would be your Control Variable,
and your current position on the road would be your Process Variable.
Your eyes are your feedback.
You adjust your steering wheel according to many factors such as the angle of your wheels,
possible wind disturbance, the position of other vehicles, that sort of thing.
You don’t do hundreds of calculations to determine your point of attack,
you intuitively, after years of driving, know what you need to do to safely switch lanes.
Because you are not blindfolded when you drive, your eyes give feedback to your brain,
allowing you to control this process through referenced feedback.
This control is considered a closed loop process.
But consider a blindfold, you would have no way of knowing where you are on the road.
This type of control would be called open loop control.
Obviously, a much more difficult process to control and on occasion, you may run into this type of control in your career.
In an industrial plant, since there are many factors that we need to consider,
we need a robust controller that takes our parameters into account
and does hundreds of calculations to determine where the process is and where it needs to go.
Say we need to control gas flow through a pipe.
The Setpoint of gas flow is calculated based on a calculation of some factors.
This Setpoint can change at any time based on the parameters used in the calculation.
We will control this flow based on a modulating valve.
In this case, the more open the valve, the more gas allowed to flow.
The requested position of the valve is our Control Variable.
Downstream of this modulating valve we have a flow meter that will measure the gas flowing through the pipe,
this is our feedback or our Process Variable.
In this example, we are going to use a PLC function block in order to control this process.
Our PID block will be able to use the parameters we specify
to determine the controller's reaction to our process.
Let’s take a step back and talk about the parameters that we will be adjusting for our control.
First, the PID term, as stated earlier, stands for Proportional, Integral, and Derivative.
These parameters can be used individually or collectively.
Meaning, you can have just a proportional controller, a proportional and integral,
a proportional and derivative, or of course a proportional, integral, and derivative controller.
Each of these parameters is enabled and adjusted individually
and each controller type would be used for specific purposes.
Each parameter having a specific impact on the way the controller functions.
To sum it all up, we, as control engineers, need to control processes and in order to do that,
we use devices available to us in order to facilitate that function.
The stand-alone and integrated PID controller is the most widely used device for that purpose.
In our next video, we will get into the nitty-gritty of how to adjust the parameters of our controller.
This is often referred to as Tuning the loop.
Head on over and see how it’s done.
Want to learn PLC programming in an easy to understand format
and take your career to the next level?
Head on over to realpars.com