Control Systems

Proportional-Integral-Derivative (PID) Control Systems

Proportional-Integral-Derivative

For processes that are able to operate with continuous cycling, the relatively inexpensive two position controller is sufficient. For processes that cannot tolerate continuous cycling, a proportional controller is used. For processes that tolerate neither cycling nor offset error, a proportional plus integral/reset controller can be used. For processes that require improved stability and can tolerate an offset error, a proportional plus derivative/rate controller is used.

Nevertheless, there are some processes that cannot tolerate offset error, yet need good stability. The rational solution is to use a control mode that combines the advantages of a proportional, integral and derivative (PID) action.

Proportional plus Integral plus Derivative Controller Actions

When an error is introduced to a PID controller, the controller’s response is a combination of the proportional, integral and derivative actions as illustrated in Figure (a).

Suppose the error is due to a slowly increasing measured variable. As the error increases, the proportional action of the PID controller produces an output that is proportional to the error signal. The integral action also called the reset action of the controller produces an output whose rate of change is determined by the magnitude of the error. In this case, as the error continues to increase at a steady rate, the integral output continues to increase its rate of change. The derivative action also called the rate action of the controller produces an output whose magnitude is determined by the rate of change of the error signal, and not the amplitude/magnitude of the error. When all these actions are combined, they produce an output illustrated in Figure (a).

PID Control Responses
Figure (a) PID Control Responses

Note that, these response curves are drawn presuming no corrective action is taken by the control action. In practice, as soon as the output controller begins to reposition the final control element, the magnitude of the error should begin to decrease. Ultimately, the controller will bring the error to zero and the controlled variable back to the setpoint.

Figure (b) below demonstrates the combined controller response to a demand disturbance.

Figure (b) PID controller Response Curves

The proportional action of the controller stabilizes the process. The integral action combined with the proportional action causes the measured variable to return to the setpoint. The derivative action combined with the proportional action reduces the initial overshoot and cyclic period.

Related articles:

Share
John Mulindi

John Mulindi is an Industrial Instrumentation and Control Professional with a wide range of experience in electrical and electronics, process measurement, control systems and automation. In free time he spends time reading, taking adventure walks and watching football.

View Comments

Recent Posts

What to Expect from PCB Assembly Services in China

The importance of printed circuit board (PCB) technology has escalated throughout the years with the…

2 days ago

Magneto-Optic Current Sensors for High Voltage, High Power Transmission Lines

One of the key challenges in measuring the electrical current in high voltage, high power…

4 days ago

How the Wiegand Effect is used in Sensing Instruments

The Concept behind Wiegand Effect Based Sensors   The Wiegand effect technology employs the unique…

6 days ago

Piezoelectric Accelerometer: Principle of Operation & Applications

An accelerometer is a sensor that is designed to measure acceleration or rate of change…

1 week ago

The USB-6009 Data Acquisition Card Features

The USB-6009 is a small external data acquisition and control device manufactured by National Instruments…

1 week ago

How X-Y Tables are used in Position Control Applications

X-Y tables are utilized as components in many systems where reprogrammable position control is desired.…

2 weeks ago