THERMOSWITCH® controllers control temperatures as low as -100oF (-73oC) and as high as 600oF (316oC) with the proven dependability of over 75 years of service to satisfied customers.
Principle of operation
The THERMOSWITCH® controller is a strut-and-tube type thermostat comprised of two basic parts: the outer shell, made of high-expanding stainless steel and the strut assembly, made of low-expanding metal.
A pair of electrical contacts is mounted on the strut assembly and installed in the shell under tension or compression. Since each end of the strut assembly is mechanically connected to the ends of the shell, a net change of force is produced on the strut assembly as the shell expands or contracts with changing temperature. The temperature at which the contacts “make” or “break” can be regulated by a temperature adjusting sleeve.
This adaptation of the differential-expansion principle gives several important control advantages:
• Fast Response – The outer shell of the THERMOSWITCH® is an active sensing element, and not merely a housing, response to temperature change is almost instantaneous.
• Close Control – The controller’s shell and strut arrangement has “anticipation” characteristics which substantially reduce the amount of overshoot and undershoot during conditions of rapid temperature change. Anticipation is produced by an inherent time lag between the shell and struts, which causes the shell to “lead” the struts by an interval that varies with the rate of temperature change. With rapid temperature rise, the shell exerts a larger net force on the struts and tends to pull them apart sooner than if the temperature were rising slowly. The result is several degrees or more of anticipation which helps produce closer control.
• Extreme Sensitivity – The strut and contact operates by slow make and break. This means that every temperature change, no matter how small, causes a corresponding change in the space between the electrical contacts. Therefore, contact action can be produced by a very small temperature change, which accounts for the THERMOSWITCH® controller’s excellent resolution sensitivity of 0.1ºF (0.05ºC).
• Vibration Resistance – Since the strut assembly is assembled under tension or compression, a properly installed unit has excellent vibration resistance and will provide great control under difficult physical conditions.
• Agency Approved – Various models are listed Underwriters Laboratories (UL) and certified by the Canadian Standards Association (CSA) and compliance with applicable European norms for acceptance in the EU under the CE marking scheme.