How to choose the bimetallic thermometer watch brand?

The bimetallic thermometer works by using the different expansion coefficient of two kinds of metal ( Or alloy) Piece together form a thermal components, generally made spiral wound, its end ( The free end) Equipped with a pointer. When the temperature changes, the thermal component of curvature change, free end rotation, drive the pointer indicates the temperature value on the dial. Generally there are two kinds of bimetal thermometer table card, one is the bottom of the aluminum, the other is a white background ( Is above the table card of the aluminum coated with a layer of white paint) 。 So how to choose the bimetallic thermometer watch brand? From the buyer's point of view, the role of the table card is according to temperature, so choosing white and aluminum background difference, basically see personal likes. And from the Angle of the bimetallic thermometer manufacturers consider is not the same, there is a process problem, generally choose the bottom of the aluminum when temperature range is less than 250 c and white can be, but after more than 250 c temperature, may melt, the paint of the white table card so it's best to choose the bottom of the aluminum.