When an industrial furnace, oven, or kiln is heat-treating a part and something goes wrong with a heating element, there is a risk that the PID temperature controller could have a run-away condition – causing the furnace to heat up to the point that it destroys itself and the critical parts inside. For that reason, the furnace is often fitted with a “limit-alarm controller” that shuts down the process by disconnecting power should the temperature reading exceed a specific value (High-Limit). There are Low-Limit alarm controllers as well for special applications. In order to guarantee that these have been fully tested, Factory Mutual provides a Standard 3545 that the limit controller must meet in order to be suitable for protection purposes.
Eurotherm by Schneider Electric has long been one of the premiere suppliers of high accuracy PID temperature controllers that are trusted in furnaces and ovens for the aerospace, automotive, pharmaceutical, and other heat treating markets. Eurotherm’s newest brand of controller, the EPC series, has now received FM approval for doing Hi or Lo temperature limit alarming as an option.
Traditionally, the limit alarm controller was always a separate controller within the furnace control panel, however, recent changes have seen many companies start to use a single controller that functions both as the PID controller and separately has a limit alarm control option. The Eurotherm can now be used either way.