PLC & PID Control: What’s Right for Your Industrial Automation Process

A common misconception that arises every now and then is the relationship and function of Programmable Logic Controllers, or PLC, and Proportional Integral Derivative Controllers, PID controllers.

These two control systems, although both will monitor and control industrial automation systems, however, the misconception can be that either can perform the function of the other. Although on occasion this is true, however, the desired quality of the result can differ greatly.

PLC: Programmable Logic Controllers

The Programmable Logic Controllers are fundamentally a discrete control system, which is essentially a control system that uses a limited number of states for inputs and outputs, or more simply, lots of on and offs.

This type of controller can often be found on systems such as bottling process plants, such as filling bottles, applying labels and packaging, where each stage’s criteria is met with yes or no, allowing or disabling the process to progress to the next stage.

PID: Proportional Integral Derivative Controllers

Proportional Integral Derivative controllers however rely on a significantly more granular feedback system to control a process and achieve consistent quality output. What this essentially means is that PID-controlled processes will monitor their process continuously if it is in line with the programmed setpoint, and if not, it will adjust itself to refine the process to minimise error.

For example, within biscuit production, if the biscuit is undercooked, a moist biscuit will crumble upon packaging, whereas if it is overcooked, the biscuit may fail the manufacturer’s quality criteria, such as colouration and texture. To avoid these outcomes and apply greater control of the output quality of the biscuits, a PID Controller can be deployed within the baking process.

The PID Controller can take multiple temperature inputs (e.g. air temp, conveyor temp, airflow etc) from each of the zones and stages within the oven (top & bottom, start and finish) to ensure sufficient heat is produced by the burners to achieve a consistently coloured and delicious biscuit. If a zone isn’t consistent with the setpoints, a PID controller can take on the error and self-tune, controlling the burner's input to match the setpoint.

To learn more, visit our range of  Proportional Integral Derivative Controllers, here. 

To learn more about Watlow Thermal Control Solutions.

To learn more about Eurotherm Process Control Solutions.

The Right Tool for the Right Task

As mentioned previously, the PLC and PID control system can be used on occasion to perform the role of the other, however, the impact of doing so can perhaps lead to unnecessary waste of resources and/or produce an end product with inconsistent quality from batch to batch.

However, as technology has advanced, industrial automation process technologies have begun integrating aspects of both control systems into the same device, with some PLCs providing users with limited PID loop control, and other PID controllers providing users with limited PLC control. In this instance, ADM Systems can cater to users with such needs with the use of a Process Automation Controller, or PAC for short.

Process Automation Controllers 

The Process Automation Controller may provide the ideal combination of PLC functionality and high-accuracy PID Loop Control, whilst also providing coverage with redundant central processor units, CPU, variety of programming languages and the ability to incorporate advanced control strategies.

To learn more visit our Eurotherm PAC T2750.

Let us help you find the right tool!

Investing in the right PLC and the right PID control system can make all the difference in creating consistency of quality in your production, but it can be tricky to decide where and which options your production needs, but don’t worry, the experienced ADM Instrument Engineering team is here to help.

Call the team on 1300 236 467 or send an enquiry via our contact page.