PID stands for proportional-integral-derivative controller. This is a device used in control systems or simply to control other devices or other electronic systems. The main function of this controller is to help regulate or maintain the level of the different variables in the control system. The PID controller may function affecting only a single device or many other devices simultaneously. The typical application of the PID controller is found in the industrial and manufacturing areas.
One of the various applications of the PID is the common temperature control of a particular household or area in a building. The thermostat is interfaced with a PID controller and the latter maintains or regulates the temperature of the area based from the desired temperature. This desired temperature is referred to as the setpoint or the ideal temperature. If the surrounding temperature rises or falls, the PID adjusts the level so that the thermostat maintains the desired level. Herein, the changing value of the temperature is the variable. PID controls this variable, which is changing with time, and tries to maintain the setpoint by varying the variable to meet the ideal temperature.
PID controllers and normal controllers are distinguished in the way each device function or based on their application. PID controllers employ advanced formula to contain and or preempt any flaw with the system. With PIDs, the smooth application or performance of the system is ensured to be as error-free as possible.
What is the advanced formula which the PID controller is using? This if oftentimes referred to as the algorithm. Algorithm simply provides for the procedures to be executed based from what is the current status of the device or what to do when certain factors have changed. Algorithm is a step-by-step process. This is similar to a magazine quiz or questions that direct the person answering the same to proceed to the next level based upon his input or given answers. In other words, algorithm executes procedures based on an indefinite actions or variables.
The PID controller works with a feedback loop. A feedback loop is a condition wherein a response, referred to as a feedback, is sent to the controller by the device receiving information from the same controller. Based from the received input from the device which responded from the information the controller has sent, the latter formulates a decision on how to formulate solution and sends it back again to the device, thus a continuous loop is created.
With PID controller, one big advantage is apparent, that is, various devices may be controlled with minimal human intervention. With this, other employees may be able to work on other tasks and multi-tasking can be done at a given time. The only drawback to this is that PID must be tuned. This means that certain adjustments must be made upon the settings of the device so that the desired outcome is produced. In setting the parameters of the PID, technical knowledge or personnel who are expert in the programming of PIDs must be employed which would cost some more.
Physical implementation of PID control
In early times, PID controllers were mechanical devices that can produce automatic process control. These mechanical devices employ a lever, a mass, a spring and are often powered by compressed air. The compressed air, or pneumatic controllers, in those times were the industry standard.
Interface solid-state or tube amplifier, resistors and capacitors can produce electronic analog controllers. What are the applications of electronic analog controllers? Most complex electronics systems like head positioning of a disk drive, motion sensors or movement-detection circuitry of seismometer, and power conditioning of most power supply uses electronic analog controllers. With the advancement from analog to digital, the analog controllers are now replaced by digital ones using the microcontrollers or FPGAs.
Programmable logic controllers (PLCs) are implemented in most modern PID controllers. Sometimes, panel-mounted digital controller is used. The main advantage of this is that this is driven by a software, which means that the flexibility as regards the implementation of the algorithm can be a great benefit.
Limitations of PID control
PIC controllers find applications with many devices that needs to be controlled and performs well even in very minimal tuning or tweaking. However, PIDs do not perform well with some applications and do not provide optimized control. The main drawback of PIDs is that is a feedback system, with fixed parameters or values, and is unaware of the entire process. Therefore, the overall performance is reactive and a compromise in these ways:
1. PID controller can best control the devices but it has no pattern of the process; and
2. if the pattern of the process is incorporated in the PID controller, the outcome would be more desirable.
So how can the PID be tweaked or remedied in order to achieve the best performance of the system being controlled? The necessary remedy is to include a feed-forward control with information about the system. The PID is just used to contain the errors. PIDs can also be altered in some small ways such as modifying the parameters. This could be done by either scheduling gain in various usage or application, or changing them to adapt to circumstances based on the performance. Also, a higher sampling rate, accuracy, low-pass filtering for precision could be used, or interfacing in cascaded systems different PID controllers can be used to tweak PIDs. This is the main reason why PIDs are used in cascades because PIDs perform poorly when used in as a single unit. PIDs also suffer a drawback in the non-linear systems as regulation may be trade off as against response time. They also are not reactive to the altered process behavior (especially when the system changes as it warms up during the powering up stage) or experiences lag in delivering response to greater changes in the system.