The Essential Guide to Open Loop and Closed Loop Systems

There are two types of control systems in automation – open and closed loop. You may have come across these terms and been unsure of what open-loop systems and closed-loop systems are, or which to choose.

Automation and control terminology can be confusing at first. But decoding automation is easy with the right help. This essential guide to open-loop and closed-loop systems explains it all, from what open and closed-loop control means, to their unique benefits.

What is an Open Loop Control System?

An open-loop control system is a form of manual, or only partially automated, control. A human operator is often required for this type of control. This operator will set the input value or correct any errors, according to their experience with the machine in question.

The open-loop system does not have any feedback loop to monitor, and it does not adjust itself based on its output. Therefore, it operates entirely independently of its output.

Everyday Examples of an Open Loop System

A basic household toaster is a good example of an open-loop system. The user of the toaster has some control over the input, by placing the slices of bread into the toaster. They can also manipulate the time and temperature by using the toaster’s dials.

But other than these inputs, the user will only know when the bread has started and finished toasting, and then they can judge the output – the quality of the toast. The output (toast quality) does not affect the input (the bread and the timer/temperature dials).

Benefits of an Open Loop System

Despite its shortcomings due to the absence of a feedback loop, open-loop systems are nonetheless popular for several reasons.

Open-loop systems:

• Are much simpler to design and also for your workers to understand. Therefore, they are much easier to implement, maintain, and when necessary, repair.

• Due to the lack of continuous monitoring, assessing, and adjusting involved in a feedback loop, the system may operate slightly faster than a closed one would. However, this depends on the processes involved.

• Because they don’t rely on feedback like a closed system does, they are immune to any noise interference and other issues. (Such interference can sometimes interfere with a closed system’s feedback loops).

What is a Closed Loop Control System?

Unlike an open-loop system, a closed-loop control system is a form of automatic control with continuous monitoring, measuring, and assessing taking place. This type of control can often be achieved without a human operator, or with very little involvement from them.

Also unlike an open loop, it incorporates feedback to adjust its control actions based on the output. The closed-loop system continuously monitors its output, making any necessary adjustments to the input control to maintain the desired output level.

Because of this feature, it is more accurate for industrial automation control than an open-loop system.

Therefore, a closed-loop control system is favored in the industrial environment. It continuously monitors output using sensors and compares it to a reference input. Should there be a discrepancy, an error signal is generated and adjustments will be made to ensure the desired output.

Example of a Closed Loop System

A thermostat-controlled heater is the perfect example of a closed-loop control system. The thermostat measures the ambient temperature and compares it with the desired temperature. If they differ, the thermostat sends a signal to the inner heating/cooling mechanisms to adjust the temperature.

The thermostat continuously monitors the temperature and sends feedback, as many times as necessary, to achieve the output – the desired temperature. This constant back and forth between the measurement, comparison, and adjustment, is the feedback loop known as a closed loop.

This is why closed-loop systems are commonly used for HVAC automation and control systems.

Benefits of a Closed Loop System

Their self-regulation and adaptability make closed-loop control systems a good choice for industrial automation.

Closed loop systems:

• Continuously monitor processes to align the output with the desired input. This leads to greater accuracy in the industrial sector.

• Adapt to changing conditions on-site, making them a versatile choice for extreme environments.

• Operate efficiently, with less waste, thanks to the automatic monitoring and adjustment of its feedback loop. This conserves resources, saving your business money down the line.

• Self-regulation with little to no human intervention, which is the ultimate aim of automation.

Conclusion

Once you understand the basic mechanisms of open and closed-loop control systems, it’s easy to see why closed-loop systems are favored in the manufacturing and industrial sectors. But whichever system you choose, you need top-quality components.

At AEC, we have the industrial automation systems, industrial control panels, consoles, and components you need to keep your business going and keep it growing. Contact us today, and find the control you need.