With the development of science and technology and the needs of modern industrial technology, temperature measurement technology is constantly improving and improving. As more and more wide temperature range, according to different requirements, but also to create different needs of the thermometer device. Here are several.
1, the gas thermometer
Multi-temperature materials for hydrogen or helium, hydrogen and helium liquefaction because of the very low temperature close to absolute zero, so it is very wide temperature range. Such a high precision thermometer, are used for precision measurement.
2, resistance thermometer
Into metal and semiconductor resistance thermometer resistance thermometer, are based on changes in resistance with temperature made this feature. Metal thermometer mainly useful for platinum, gold, copper, nickel and rhodium iron of pure metal, phosphor bronze alloy; semiconductor thermometer mainly carbon and germanium. Resistance thermometer easy to use and reliable, has been widely applied. Its measurement range is -260 ℃ to 600 ℃ or so.
3, thermocouple thermometer
Is a widely used industrial thermometer device. Made use of thermoelectric phenomena. Two different metals welded together to form wire work side, the other at both ends and measuring instruments connected to form a circuit. End work on the measured temperature Department, work does not end with the free end of the temperature at the same time, there will electromotive force, hence the current through the circuit. Volume by electrical measurements of the temperature using the known, we can determine the temperature of another. This thermometer and more copper - constantan, iron - constantan, nickel Ming - constantan, gold cobalt - copper, platinum - rhodium and other components. It is suitable for the larger temperature difference between the two substances are used for high temperature and low turbidity measurement. Some thermocouple to measure temperatures up to 3000 ℃, and some can measure the temperature close to absolute zero.
4, high temperature thermometer
Is designed to measure the temperature above 500 ℃ thermometer, bright test thermometer, thermometers and radiation thermometers than color. The principle and construction of high-temperature thermometers are complex, and is not discussed. The measurement range of more than 500 ℃ to 3000 ℃, not to measure temperature.
5, Analog Thermometer
Instrument panel is shaped like a thermometer, also known as the yardstick used to measure temperature, thermal expansion and contraction principle is made of metal. It is used as temperature sensing bimetallic element, used to control the pointer. Double metal is usually copper and iron rivet together, and copper in the left, the right iron. As the thermal expansion and contraction of copper significantly more effective than iron, so when the temperature increases, copper stretch bending iron to the right, pointer, driven by double-metal deflection on the right (pointing to high temperature); contrary , the temperature change is low, the pointer, led by double-metal deflection on the left (low point).
6, glass tube thermometer
Glass thermometer is used to implement the principle of expansion and contraction of temperature measurement. As the temperature expansion coefficient of the medium and the freezing point and boiling point of difference, so we have a common glass thermometer are: kerosene thermometer, mercury thermometer, water thermometer red pen. He has the advantage of simple structure, easy to use and relatively high accuracy and low cost. Drawback is that the limits and accuracy of measurement by the glass quality and nature of the medium temperature limit. And can not Remote, fragile.
7, pressure thermometer
Pressure thermometer is the use of closed containers of liquid, gas or vapor heat or pressure resulting from changes in volume expansion as a test signal. Its basic structure is a warm pack, capillary and instructions sheet composed of three parts. It was the first used in the production process temperature control methods. Pressure in situ temperature measurement system is still the direction and control of the application of a wide range of temperature measurement method. Pressure thermometers advantages are: simple structure, high mechanical strength, not afraid to shock. Inexpensive, requires no external energy. Disadvantages are: Temperature range is limited, generally -80 ~ 400 ℃; heat loss of large slow response time; meter sealing system (temperature package, capillary, spring tube) damage difficult to repair, must be replaced; measurement accuracy by ambient temperature, Package installation location influenced temperature, accuracy is relatively low; capillary transmission distance is limited. Pressure thermometer regularly measured the scope of work should be the scope of the 1/2--3/4 Department, and as much as possible to show the table with the thermometer bulb in the horizontal position. The installation package used to install bolts warm temperatures will result in the loss of temperature is not accurate, and install thermal insulation should be carried out, and as far as possible in the absence of vibration, temperature of the work environment.
8, rotation-type thermometer
Rotation-type thermometer is a curly piece of metal made double. Bimetal one end fixed and the other end connected to the pointer. Two different levels of metal sheets caused by expansion at different temperatures, resulting in different levels of bimetal coil, the resulting pointer refers to a different location on the dial from the dial readings, the temperature can be ascertained.
9, semiconductor thermometers
Change in resistance of semiconductors and metals are different temperature, its resistance, however, reduced, and the fluctuation range. Therefore a small change in temperature can also produce significant changes in resistance, the thermometer made of a high precision, often called the sensing device.
10, thermocouple thermometers
Thermocouple thermometer is composed of two different metals connected to a sensitive voltmeter formed. Metallic contacts at different temperatures, will produce different ends of the metal potential difference. Potential difference is very small, it can be a sensitive voltage meter measured. By the voltage meter readings, the temperature can know why.
11, optical measuring pyrometer
If the high temperature object to be given a lot of visible light, can be used to measure the amount of heat radiation to determine its temperature, this thermometer thermometer measurements shall be light. This thermometer is mainly equipped with a red filter and a telescope with a small light bulb, the current account and the variable resistor circuit is made. Use before the establishment of the filament corresponding to different brightness temperature and current meter readings on the relationship. When used, the telescope is being tested on material, the resistor, so the brightness and sensed the same thing, then can be read from the current meter temperature of the DUT.
12, liquid crystal thermometer
LCD made with different formulations, different from the phase transition temperature, when the phase transition, its optical properties will change, so change the color liquid crystal look. If the different phase transition temperature of the liquid crystal coated on a paper by the liquid crystal color change, he will know why the temperature. The advantages of this thermometer is easy reading, but the disadvantage is lack of precision, commonly used in ornamental fish bowl, to indicate water temperature.
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