The working principle of the stepless temperature controller involves a sensitive temperature sensing bimetallic disc that is pre-formed to a certain temperature. As the ambient temperature changes, the degree of curvature of the disc alters. Once it bends to a certain extent, it either closes (or opens) the circuit, thereby activating (or deactivating) the refrigeration (or heating) equipment.

2. Hot double metal is a composite functional material composed of two or more metals or alloys with different coefficients of expansion, which are firmly bonded across the entire contact surface and exhibit shape changes with temperature variations.

In thermoset bimetallic composite alloys, the component alloy layer with a higher coefficient of thermal expansion is generally referred to as the active layer or high expansion layer (HES). The component alloy layer with a lower coefficient of thermal expansion is called the passive layer or low expansion layer (LES). An intermediate layer with varying thicknesses is inserted between the active and passive layers to act as a conductive layer, typically including pure Ni, pure Cu, and zirconium copper, etc. This is mainly used to control the resistivity of the thermoset bimetallic, resulting in a series of resistive thermoset bimetals with essentially the same thermal sensitivity but different resistivities.

4. Invar, also known as "invariant steel," is a nickel-iron alloy composed of 36% nickel, 63.8% iron, and 0.2% carbon. It boasts a low coefficient of thermal expansion, maintaining a fixed length over a wide temperature range. Discovered in 1896 by the Swiss physicist Charles Édouard Guillaume, it is primarily used in the production of standard rulers, thermometers, rangefinders, clock pendulums, gauge blocks, resonators for microwave equipment, gravimeters, thermocouple components, and optical instrument parts. In bimetallic thermostats, it is commonly used as the passive layer.