In a previous article, Temperature Control of Air Heaters, we provided a general overview of control for process heat systems and explained the difference between closed- and open-loop controls. Briefly, a closed-loop system is output driven; the output of the system is continually measured and fed back to control components which adjust the operation of the tool to bring its output into alignment with a pre-set target. An open-loop system has no feedback loop and, as a result, the output of the tool does not impact its continued operation. For example, in a closed-loop process heat system if the inlet air increases in temperature the tool output temperature will briefly increase before the control system brings it back to set point, however in an open-loop system the tool output temperature will increase and no corrective action will occur.
In this article series we will expand on this topic, exploring when it is advantageous to use a closed-loop system and when it is acceptable to use an open-loop system. This first installment will look at the benefits of automating your system with closed-loop control and the process issues that this can help resolve.
If your application has tight tolerances and temperature requirements, then it will likely require a closed-loop control system. Including a feedback loop in your control scheme will ensure that you are getting the temperature you need, where you need it. Closed-loop control greatly increases the accuracy of a process heat system as the output is constantly being measured and adjustments are being made when necessary to keep the output on target.
Adjusting for the Environment
If the ambient temperature of your facility fluctuates with weather, with an open-loop system you can expect that your process temperature will fluctuate with the weather as well! Because a closed-loop control system is constantly monitoring and self-correcting, it will compensate for changes in the environmental conditions and make certain your process stays on target if the conditions surrounding the process heat system change.
Because the output from the process heat system is measured, you will always be aware of the system’s status. Additionally, automated alarm systems can be easily integrated into the control scheme. If there is any sort of failure, from minor to catastrophic, your system can let you know that it is off target or unable to reach the target. Knowing this information as soon as possible allows you to react quicker and minimize effects on production.
Automating your process heat system with closed-loop control is the best way to improve its accuracy and precision. It will allow you to have greater confidence in the reliability and repeatability of your system in day to day operation. Most importantly, it will help you stay in control of your process.
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