Derivatives Go into the control room of a process plant and ask the operator: Integrals without the Math Is it any wonder that so many people run scared from the concept of integrals and integration, when this is a typical definition? If you understood that you are a smarter person than me. The integral of a signal is the sum of all the instantaneous values that the signal has been, from whenever you started counting until you stop counting.
You may never have to touch those settings again! PID is a mathematical tool created by engineers and is used in controllers. What is PID for? The best way to explain what PID does, is to take an example.
Most people have been to a swimming pool at some point in their lives, so this is the example we shall use. PID is also applicable in a huge variety of other processes. If you are not sure, you can always contact us to discuss your application.
When a person enters a swimming pool, they create a chlorine demand. They do this by introducing sweat, bacteria, organic molecules and other substances into the pool water. Chlorine reacts with these substances, which results in chlorine being used up and the chlorine level dropping.
The chlorine level in this example, is often called the process variable or PV in the context of PID. In order to maintain a concentration or level of chlorine, more chlorine needs to be dosed.
If you dosed the same amount of chlorine per bather, the level would not be stable as all bathers create a different chlorine demand e. Dosing manually brings in the issue of human error, and how operators approximate or calculate the amount of chlorine to dose based on current levels.
Another issue with manual dosing is that it is not a continuous process, meaning it is unlikely a stable level will ever be reached. What does PID do? PID takes the measured level of chlorine or the PV and compares it to the desired level or set-point.
This comparison gives the error which PID interprets and then calculates an output. The output is an electrical signal which controls the dosing of the appropriate chemical.
The output can control heaters, dosing pumps and many other mechanisms that can be used to change the PV. How is it used? PID is made up of three parts, proportional, integral and derivative. Understanding what each part does helps operators choose the level of control best suited to them.
Proportional — Is the most commonly used for portion PID and suits most applications. When using proportional control, the further away the measured value is from the setpoint, the larger the output will be from the controller.
This is an appropriate level of control for most processes, and users can gain a lot of control from a purely proportional system. In some systems where the PV is lost to the process, e.
Users can see that although the process approaches the setpoint it rarely, if ever, gets to it. The user can compensate for droop if the removal of the PV is fairly constant, simply by raising the setpoint, e. If droop changes often, e. Integral — The output from the integral term is determined by both the magnitude and the duration of the error.
A small error over a long period of time will trigger a larger response than from a purely proportional system. Derivative — Derivative gain is rarely used and is generally set up only by expert engineers. Derivative gain uses the rate of change in the PV to try and predict future errors.
This type of control is particularly susceptible to overcompensating, especially if there is even a small amount of signal noise usually seen as spikes in the PV. Derivative gain is generally a tweak used by engineers to improve an already tight control, and is almost never used as an essential part of control.
What are the benefits of PID? When properly set up, PID can lead to far tighter process control, which in turn can save you time and money.
As an example, pool managers want to keep chlorine levels low, to improve the bathing experience and also save on chemicals. AquaSense is a chlorine analyzer system that responds quickly and appropriately to a change in bather load also known as chlorine demand.PID for Dummies "I personally have a few hundred dollars worth of books on controllers, PID algorithms, and PID tuning.
Since I am an engineer, I stand a chance of understanding some of it. Electric Drives - Motor Controllers and Control Systems (Description and Applications) Purpose.
For many years the motor controller was a box which provided the motor speed control and enabled the motor to adapt to variations in the load.
Controller manufacturers arrange the Proportional, Integral and Derivative modes into three different controller algorithms or controller structures. The PID features found in the control loops of today’s controllers have enabled us to achieve much greater accuracy in our commercial control systems at an attractive price compared to .
Suitable for use in utilities and industrial environments, the SEL Real-Time Automation Controller (RTAC) is a lower-voltage version of the SEL RTAC. Proportional Integral (PI) Control A variation of Proportional Integral Derivative (PID) control is to use only the proportional and integral terms as PI control.
The PI controller is the most popular variation, even more than full PID controllers.