Thermocouple ( 热电偶) What's the meaning of _ instrument

Thermocouple 【 English name thermocouple 】 Full name: thermocouple thermometer, thermocouple is widely applied to the current industry of temperature measuring sensor products, its principle is as follows: thermocouple is one of the commonly used temperature detecting element on industry. Its advantages are: (1) high accuracy of measurement. For thermocouple direct contact with the object being measured, not affected by the intermediate medium (2) the measurement range. The commonly used thermocouple from - 50 ~ + 1600 ℃ can be continuous measurement, some special thermocouple low measurable to - 271 + 2800 ℃ as gold iron nickel chromium and tungsten - Rhenium (3) simple structure, easy to use. Thermocouple is usually composed of two different kinds of metal wire, but is not limited by the size and the beginning of, outside has protective casing, which are very convenient. Principle 1, the basic principle of thermocouple temperature measurement is to two different material a conductor or semi-conductor welding, form a closed loop. Due to two different metal carries different number of electrons, when two conductor when there is a temperature difference between the two fixation point of high potential to low potential discharge phenomenon occurs, thus formed in the loop current, the bigger the temperature difference, the greater the current, this kind of phenomenon called the thermoelectric effect, also called the seebeck effect. Thermocouple is in using this effect to work. 2, the structure of thermocouple ( 1) The structure of thermocouple in order to keep the thermocouple is reliable, steady work, the structure of its requirement is as follows: two of thermocouple electrode welding must be strong two hot electrode should be well insulated between each other, in case of short circuit compensation conductor should be connected to the free cod of a thermocouple to be convenient and reliable protection casing should ensure thermal electrode and harmful medium sufficient isolation. Installation dimensions should try to choose metric [ China standard] Such as thread: 12 x1. 5、16 x1。 5、20 x1。 5,27X2,33X2mm. Flange 95, 105, 115 mm in diameter. 3, the thermocouple cold end temperature compensation due to the thermocouple materials are generally more expensive ( Especially when using precious metals) And temperature measuring points are far away the distance to the instrument, in order to save thermocouple materials, reduce cost, usually adopt the compensating conductor (of the cold junction of the thermocouple The free end) Reaches to the relatively stable control indoor temperature and connected to the meter terminals. It must be pointed out that the role of the thermocouple compensation wire only extend thermal electrode, make moves to the control room of the cold junction of the thermocouple meter terminal, it itself does not eliminate the cold end temperature change on the influence of temperature, no compensation. So, still need other correction method is used to compensate the cold end temperature t0 indicates influence on measuring temperature 0 ℃. Generally display and control instrument has automatic temperature compensation system, do not need to worry about. Instrument must pay attention to when using thermocouple compensating conductor model is suitable, the polarity can't wrong, compensation conductor should be connected to the thermocouple is generally not more than 100 ℃, the temperature here is important to note that many reproduced the technical data on the network speak: compensation conductor should be connected to the thermocouple is generally not more than 100 ℃, the temperature in fact, this is wrong! Special working conditions, can choose thermocouple extension, namely the conductor material and thermocouple electrode material consistent wire connection, such as: KX nickel chrome - Nickel silicon compensation conductor; The EX nickel chrome - Constantan thermocouple cable; JX iron - Constantan thermocouple cable; TX copper - Compensation conductor of copper nickel deposit is not the problem, according to the law of the middle of the thermocouple conductor, the compensating conductor temperature is not restricted. And some thermocouple such as: B dividing platinum rhodium - 30 Platinum rhodium 6, the thermocouple compensation conductor, in 400 degrees without accuracy using ordinary double core copper wire.