In industrial automation, ensuring that machines and processes function precisely as intended is crucial. One of the key concepts used to maintain control over processes is PID Loop Control. PID stands for Proportional, Integral, Derivative control, and while it may sound complex, PID control is a method used to maintain a desired output by continuously adjusting a system’s inputs. To help make this easier to grasp, consider PID control using simple analogies and practical industrial applications.

What is PID Loop Control?

Imagine you are driving a car and set the cruise control at 70 miles per hour. Despite varying road conditions (hills, wind resistance etc.), the car maintains this speed without further input from you, the driver. The car’s sensors (input) automatically control power to the engine (output) to maintain this speed. The built-in feedback loop ensures that the amount of power delivered ensures a smooth ride at the required speed.

Now consider the role of each of these three components in detail, namely:

Proportional control for immediate response

In the driving analogy, if the car deviates from the set speed, the proportional control adjusts the power input. The more it deviates from the set speed, the more the power output changes. For example, after braking it adds enough power to get back up to speed quickly.

In industrial automation, proportional control adjusts the system’s input based on the difference between the desired setpoint and the actual output (known as the error). For example, in a temperature control system, if the temperature is below the setpoint, the proportional control increases the heat supply.

However, proportional control alone may not get the system exactly to the setpoint. There may always be a small error, leading us to the next component.

Integral control (I) for fixing long-term errors

The cruise control maintains the speed smoothly without jerky changes due to over and under compensating. This is due to the integral control, which considers the accumulation of past errors.

In industrial applications, integral control helps eliminate persistent, small errors. For instance, if a flow control system consistently runs slightly under the desired rate, integral action will gradually increase the input to bring the system exactly to the setpoint. Yet too much integral action can lead to overshooting the target, which brings us to derivative control.

Derivative control (D) for smoothing future changes

Now, imagine driving down a steep hill and the car speeding up quickly. It is the derivative control element that predicts the future rate of error and adjusts it accordingly.

In industrial automation, derivative control provides damping by predicting how quickly the system error is changing. For example, in a pressure control system, if the pressure starts to rise too quickly, derivative control steps in to slow down the increase.

How PID works as one

A PID controller uses all three components, proportional, integral, and derivative to maintain a stable and accurate system output. Moreover, the proportional part ensures immediate corrections, the integral part removes persistent errors, and the derivative part anticipates and smooths out future changes.

Where is PID Control Used in Industrial Automation?

PID control is applicable to almost any system that requires accurate control of a variable, whether it is temperature, pressure, speed, or flow. Here are some common examples in industrial automation:

1. Temperature Control: In manufacturing processes like plastic extrusion or food processing, precise temperature control is vital. A PID controller adjusts the heating element to maintain the exact temperature.
2. Flow Control: In fluid systems, like those found in chemical plants, maintaining a consistent flow rate is crucial. A PID controller adjusts valves or pumps to ensure the flow meets the desired rate.
3. Speed Control: For conveyor belts or motors, maintaining a consistent speed is essential to avoid production errors. PID controllers adjust motor speed based on feedback from sensors to keep things running smoothly.
4. Pressure Control: In industries such as oil and gas, controlling pressure is critical for both safety and efficiency. PID controllers help maintain safe pressure levels by adjusting inputs based on real-time measurements.

Programming automation equipment for PID control

Most modern PLCs and high function inverter drives come with built-in PID loop control function blocks that simplify configuration. These blocks process the PID algorithm and generate an output signal to control the output or actuator. Moreover, programming a PLC for PID control is straightforward if you understand the process variables and how to configure the PID function block.

In summary, PID loop control is the backbone of many industrial automation systems by precise control of variables like temperature, flow, and pressure.

We have a team of specialist application engineers whose skills include PID Loop Control and a whole lot more about automation systems. Contact us to find out how we can help your business.

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