What is the three basic laws of thermocouple _ instrument

Law of homogeneous conductor can be seen, thermocouple must be made up of two different homogeneous conductors or semiconductors. Jorge electrode material uneven, because temperature ladder, will produce the attached heating electric potential. By the same kind of homogeneous material, A conductor or semiconductors) Welding on both ends of a closed loop, whatever how conductor cross section and the temperature distribution, will not produce contact potential, temperature potential phase offset, loop total potential is zero. Visible, thermocouple must be made up of two different homogeneous conductors or semiconductors. Jorge electrode material uneven, because temperature ladder, will produce the attached heating electric potential. Center conductor's law in the middle of the thermocouple loop access conductor ( The third conductor) , as long as the middle temperature is the same on both ends of the conductor, the introduction of the center conductor has no effect on the thermocouple loop total potential, this is the law of conductor in the middle. Application according to the law of middle conductor in thermocouple temperature measuring actual applications, often takes the form of hot side welding, cold end open circuit, the cold end by the wires are connected to the display instrument constitutes a temperature measuring system. Any compensation conductor connection thermocouple cold end to the digital display table read mV values, the conductor and thermocouple junction of contact potential measurement causes additional error. According to this law, it is not the error! Two contact law of intermediate temperature thermocouple loop ( Temperature T, T0) Between thermoelectric potential, equal to the thermocouple in the thermoelectric potential when temperature T, Tn and when the temperature of Tn, T0 algebra and thermoelectric potential. Tn said the middle temperature. Due to the thermocouple E - application Usually non-linear relationship between T, when the cold end temperature of 0 degrees Celsius, cannot use the known loop real thermoelectric potential E ( t, t0) Directly look-up table to calculate the temperature value of hot end; Also can't use the known loop real thermoelectric potential E ( t, t0) Direct look-up table to calculate the temperature value, plus the cold end temperature to determine the measured temperature value of hot end, should be carried out according to the laws of the intermediate temperature correction. Beginners often not according to the law of middle temperature to fix! Reference electrode's law, this law is special personage research, attention to the production, use the link don't know, very simple explanation is: made from high purity platinum wire standard electrode, assumes that the nickel chrome - Nickel chrome thermocouple is negative, respectively, and the standard electrode pairs, their value is equal to the sum of the nickel and chromium - The value of nickel and chromium. USES three wire thermocouple from thermocouples work side ( Hot side) Raises the grounding wire, so to interfering voltage will be a short answer. Thermocouple is through the grounding wire to the ground of the voltage drop. Because the ground resistance is very small. So the thermocouple of almost at the same potential. To eliminate the interference effect is very good. Wire should use high temperature resistant and added material of thermocouple does not produce harmful effects. On chrome aluminum thermocouple nichrome wire available; For platinum rhodium thermocouple available platinum or a platinum rhodium wire. Thermocouple protection tube grounding the thermocouple protection tube of metal, to eliminate the interference effect is very significant. Because after grounding protection tube, interference current along the protection tube to, rather than into the thermocouple. For precious metal thermocouple, the protection tube is made of alumina, alumina is an insulator, then you can use plus heat-resistant steel tube or carborundum tube to ground.