Temperature limiting devices provide crucial protection for temperature-controlled process systems, ensuring the safety of personnel and equipment while guaranteeing high product quality. This article details the necessity of using temperature limiting devices, explains their working principles, why they can reduce risks, and provides a simple guide to selecting appropriate temperature limiting devices.
What are the risks associated with temperature control systems?
Failure of temperature control can potentially lead to equipment damage and serious safety incidents, such as a fire caused by the system's failure to promptly identify and prevent extreme temperatures. Without temperature limiting devices, every temperature control application faces these risks, and the larger the scale of the application/process materials, the higher the risk.
To mitigate risks, stringent regulations have been developed for specific industries and applications. For example, in the United States, ovens and furnaces must comply with NFPA (National Fire Protection Association) regulations. NFPA Standard 86 for Ovens and Furnaces aims to minimize fire and explosion hazards in commercial and industrial material processing and explicitly mandates the use of temperature-limiting devices.
For Class A, B, C, and D ovens, dryers, kilns, direct-fired incinerators, and other various enclosed heating systems and related equipment used in the materials processing industry, NFPA 86 standard specifies in detail the requirements for safe design, installation, operation, inspection, testing, and maintenance. In addition, NFPA 86 standard also provides specific regulations for kiln heating systems, safety equipment and applications, and fire protection.
What is the working principle of a temperature limiting device?
Temperature limiting devices are mainly used in process control to prevent temperatures from being too low or too high, protect products or equipment from extreme temperatures, and ensure that the application meets safety or quality requirements.
Temperature limiting devices are typically used in conjunction with thermocouple sensors or RTDs (resistance temperature detectors) to provide a relay output and issue an alarm in hazardous situations. Furthermore, in a loop control system, the temperature limiting controller can adjust the input temperature based on the measured temperature of the material. Additionally, the temperature limiting device has high and low temperature cut-off functions; if the temperature exceeds a preset value, the system will immediately shut down.
Why can temperature limiting devices reduce risks?
Protected by a temperature limiting device, if the system temperature exceeds the limit, the system power supply will switch to fail-safe mode, significantly improving safety. Operators set a setpoint on the temperature limiting device; once the set temperature is reached, the device sends a signal to ensure process safety, such as cutting off the heater power or activating forced cooling. It is important to note that whether the system failure is caused by a temperature exceeding or falling below the setpoint, the temperature limiting device must be manually reset for the system to resume operation. Manual reset is a key factor in reducing risk; ensure that safety conditions are manually checked before resetting the temperature limiting device.
Typical applications and industry standards of temperature limiting devices
As mentioned earlier, temperature limiters are widely used in various applications and are a powerful tool for ensuring system safety. Standards such as NFPA 86 provide detailed specifications for the installation of temperature limiters. Furthermore, FMGlobal has made significant contributions to the standardization of temperature limiter applications. FMGlobal is a US-based mutual insurance company with branches worldwide, providing excellent loss protection services to large enterprises around the world.
FMGlobal's 3545 standard "specifies the performance requirements for temperature limiting devices and control switches in industrial heating control systems, aiming to improve the operational safety of electrical switches to achieve safe shutdown or timely alarm under abnormal conditions. This standard also certifies process temperature controllers and/or temperature recorders with temperature limiting and/or temperature control functions."
In Europe, the EN14597 standard applies to "electrical or non-electrical temperature control equipment that controls temperature by controlling the power supply to a heating system, and temperature limiting devices that prevent the temperature of a heating system from exceeding a limit."
Conclusion
Temperature limiting devices help operators meet new industry standards, ensure high profitability and employee safety in factories, and improve overall performance, making them an essential tool for all temperature control applications.
