How Does The Digital Thermometer Measure The Temperature

Thermometer is a tool that can accurately judge and measure temperature. It is divided into pointer thermometer and digital thermometer. A variety of thermometers have been designed and manufactured according to different purposes.

How it works edit

A variety of thermometers have been designed and manufactured according to different purposes. The basis of its design includes: the phenomenon of expansion and contraction of solid, liquid and gas under the influence of temperature; under the condition of constant volume, the pressure of gas (or steam) changes due to different temperature; the effect of thermoelectric effect; the change of resistance with temperature; the effect of thermal radiation, etc.

1. Gas thermometer: mostly hydrogen or helium is used as the temperature measuring material, because the liquefying temperature of hydrogen and helium is very low, close to absolute zero, so its temperature measuring range is very wide. This kind of thermometer has high accuracy and is often used for precise measurement.

2. Resistance thermometer: it is divided into metal resistance thermometer and semiconductor resistance thermometer, which are made according to the characteristic that the resistance value changes with the temperature. Metal thermometers are mainly used for platinum, gold, copper, nickel and other pure metals, as well as rhodium iron, phosphor bronze alloy; semiconductor thermometers are mainly used for carbon, germanium and so on. Resistance thermometer is easy to use and has been widely used. Its measuring range is from - 260 ℃ to 600 ℃.

High precision thermometer

3. Thermocouple thermometer: it is a kind of temperature measuring instrument widely used in industry. It is made of thermoelectric phenomenon. Two different kinds of metal wires are welded together to form a working end, and the other two ends are connected with the measuring instrument to form a circuit. Put the working end at the temperature to be measured, when the temperature of the working end is different from that of the free end, electromotive force will appear, so there is current passing through the circuit. Through the measurement of electrical quantity, the temperature of another place can be measured by using the temperature of the known place. It can be used between two substances with large temperature difference, and it is mostly used for high temperature and low turbidity measurement. Some thermoelectric couple can measure high temperature up to 3000 ℃, some can measure low temperature close to absolute zero.