International Appliance Manufacturing 2008 - (Page 51) safety agencies have determined a specific set of operating specifications to protect the end consumer. It is necessary to first select a thermal control that has been evaluated for use in the end application. Once you examine the design parameters of your particular application, you can then determine the operating characteristics for the thermal control device. Almost every type of control comes in a variety of operating configurations from which you can choose. Do you need the device to open or close a circuit upon increases in the ambient temperature? Do you need an automatic reset device or a manual reset device or do you need a device that really does not reset at all? Or do you need a device called a self-hold thermal control which once it breaks the electrical circuit, an integrated heat source prevents the device from resetting until the power supply to the application is removed. There are thermal controls which meet the operating requirements of each application. Once you select the desired performance parameters for the thermal control in your application, one must consider the applied voltage and operating current. Is the current load resistive or inductive? Will the thermal control be used to break or make the full electrical load or will it be used only to monitor the operating temperature. These factors aid in the selection process to determine the precise operating characteristics of the thermal control that is required to optimize the performance of the end product. Creep action thermal controls are a single bimetallic element that generally carries the circuit current in the application. These devices obtain their name by the slow break and make movement of the bimetallic element. These devices are excellent for use in temperature controlling applications. These devices have minimal differential between their break and make points which makes them excellent for use on low voltage DC applications and applications up to 125 VAC. Snap action thermal controls also derive their name from the manner in which they operate. These devices normally utilize a specially formed single bimetallic element which increases the amount of temperature differential between their break and make points. The devices actually make a faint snapping sound when the bimetallic element activates due to increases or decreases in temperature. Because of their faster acting bimetallic elements this family of thermal controls is excellent for use in higher voltage and current applications, both on resistive and inductive type loads. Disc type thermal controls derive their name from the actual form of the bimetallic element utilized in these devices. These devices are part of the Snap Action family of thermal controls in that they International Appliance Manufacturing 2008 51
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