The structure and its principles
The bimetallic expansion thermometer is made based on the principle about expanding with heat and contracting with cold. It is usually composed of temperature—sensing element、metallic bushing、conducting shaft、indicator、dial and installing fixing devices, etc.
Two kinds of sheet metals which differ greatly in coefficient of expansions due to heat compositing together calls thermo bimetals. The temperature—sensing element means to cut the bimetals up and twist into a spiral or other suitable forms. When it is to make bimetallic expansion thermometer
, it is usually to put the temperature—sensing element into the metallic bushing and then fix the one send at the bottom of the bushing( that is the fixed end). Meanwhile, the other one is to be connected to the indicator( that is the free end) through conducting shaft.
When the temperature is changing, the temperature—sensing element will appear to roll up or loosen, bringing about the movement of the free end and then the angel variation of the indicator through conducting shaft. The angel of the rotation of the indicator has a linear relation with the temperature shift. After calibration, the temperature can be measured.
The range of temperature: -80~500℃；
The accuracy of temperature measurement: 1.5%，1.0%；
The resolution ratio: 1~5.0℃；
The thermal response time: ≤40S；
The diameter and length of the sheath: level: Φ12、10、8、6、4；
The mounting thread: M27x2
The dial diameter: 150，100，60、40、25；
Protection level: IP55
The error of the adjustment of angel: it can not exceed 1.0% of its range;
The return difference: the absolute value is not greater than its basic error limit;
The repeatability: it is not greater than 1/2 of the basic error limit;
The operative norm: JB/T8803、JJG226.
The levels of protection: JB/T8803、JJG226。
Classifications and Applications
The bimetallic expansion thermometer can be classified as axial type、radial type、135 degree angel type and universal type according to the directions between the dial and bushing; it can be classified as ordinary type、electric contract alarming type and remote signal type according to the functions; it can be classified as ordinary type、shatter—proof type、explosion proof type、water proof type according to the environment. The bimetallic expansion thermometer is applied in the middle and low temperature(-80~500℃). If there is no external power, it can be the ideal thermometer that is used on the spot to indicate the temperature. Also, it is an alternative to a liquid meter, which is widely used in many industries like petroleum、vessel、machinery and medicine.