• By Jason Sanders, Connor Wegner
  • July 31, 2020
  • Channel Chat

By Jason Sanders and Connor Wegner

Manufacturers today face many hurdles in their manufacturing applications. Process parameters can range from one application to the next. While some applications require very little precision and control system manipulation, others can be more complex and require further feedback for a more precise and repeatable process. In situations where temperature regulation is required, industrial heating requirements follow a similar path to other process controls. In temperature regulation, there are two types of systems: open loop and closed loop. Deciding which methodology to choose depends on the requirements of the process.

Open-loop heating

Open-loop heating uses manual manipulation to regulate temperature. There is very limited feedback or control features for temperature control. Open-loop heating regulation is achieved by either voltage manipulation to the heater, increasing or decreasing the amount of airflow, or utilization of an onboard potentiometer, if available. This method relies upon manual intervention by the operator to control the system at any point during the process.

The open-loop heating system has some advantages, including design simplicity and ease of maintenance. With only voltage applied to a heat source, this method does not require an elaborate control system to manipulate the temperature, which makes it easier for the user to implement the necessary components into the system. It also simplifies troubleshooting for maintenance purposes when necessary. There are also disadvantages to this method. Some of the disadvantages are inaccuracy of the system itself and no opportunities for automatic adjustments. Since there are no means for feedback to a temperature controller or programmable logic controller (PLC), the system does not have a way to make the necessary adjustments to optimize the process.

Closed-loop heating

Closed-loop heating is a method to accurately control and maintain temperature during the process. This method contains a feedback loop in which a control system receives feedback from the process and develops a response to achieve stability. It can be used for many heating applications and is an effective control method in process heating due to its ability to provide a stable and accurate temperature. A closed-loop heating system comprises a heat source, means for temperature feedback (i.e., thermocouple), and controller. In a closed-loop heating system, the controller—usually a PLC or a temperature controller—receives a signal from a temperature sensor, thermocouple, or infrared thermometer. This signal is a measurement of the temperature at a designated location in the system. This signal is then returned to the controller, where it will adjust the power given to the heater to maintain a temperature set point.

The closed-loop heating system has some advantages, such as overall system accuracy and ease of integration. Because this method can account for unexpected changes in the process, such as variations in ambient temperature or pressure, shifts in supplied voltage, or wind and air flow shifts, it gives the system the ability to manipulate the process automatically from an external controller.

Even though closed-loop heating systems can be an efficient method for a variety of industrial processes, they do have some drawbacks. This method requires a more complex control scheme and is costlier to implement and maintain. Since closed-loop heating relies upon various components for precision feedback and optimized control, the system can incur additional hardware/software costs versus an open-loop system, which can vary depending on the intricacy of the controls. In addition to increased equipment costs, more frequent maintenance activities, such as routine checks for the proper system operation, can increase.

Many variables

There are many variables to consider when deciding between an open-loop or closed-loop heating control system for an industrial application. Both methods offer great benefits, but choosing which is better suited for the process will depend upon the requirements of the end user and the application. Having a good understanding of the requirements can help companies design and implement a heating system that is both reliable and safe for end users. To help navigate system requirement and equipment options, end users should rely upon experienced consultants to find suitable solutions for their applications.

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About The Authors

Jason Sanders is both the product specialist and manager for the Industrial Heat division at Leister Technologies LLC, a plastic welding and hot-air technologies company based in Itasca, Ill. Sanders earned an AAS in computer-aided design, a BA in business management and leadership, and an MBA.

Connor Wegner is a technical sales and support associate for the process heating division at Leister Technologies. After receiving his BS in chemical engineering in 2017 from Illinois Institute of Technology, he joined Leister Technologies as an associate product specialist for process heating products.

Leister Technologies is a member of the Control System Integrators Association (CSIA), founded in 1994 as not-for-profit professional association of over 500-member companies in 40 countries advancing the industry of control system integration (www.controlsys.org).