Compensation conductor index number and polarity judgment _ instrument

We know that the compensating conductor is the extension of the reference junction of the thermocouple, have the effect of mobile reference end position, extending the reference side temperature should be a constant or with itself has reference end temperature automatic compensation device, otherwise still may be due to the new reference measurement error caused by the temperature variation. Reliable testing method is commonly used, is to compensate the ends of the wire stripping insulation layer, the two wire twisted together to make the hot end of thermocouple, into the boiling water, two at the other end of the wire are connected to the dc potentiometer ( Should not be connected to the moving coil direct reading mV table, for measuring take the current when it is low) , the measured thermoelectric potential compared with table 1, and relatively close to that of compensation wire index number, depending on the potentiometer is the cathode can be determine the polarity of the compensating conductor. Due to the test by the compensating conductor when the temperature of the reference junction of the thermocouple is not necessarily the 0 ℃, is 20 ℃, for example, the thermoelectric potential is measured under reference end thermoelectric potential value of 0 ℃. In some unknown degree, compensating lead wires, for example, such as reference end temperature 20 ℃, measured values such as in 3. 928±0. 150 mv range, can determine the compensating conductor index number is K. 3. 928 K is dividing thermocouple 100 ℃ and 20 ℃ thermoelectric potential difference, 0. Number is 150 K dividing common compensation conductor should be tolerance. The location of the compensating conductor dashboard connection point for early match the moving coil instrument thermocouple, five Ω, 15 Ω two line resistance requirements, when the thermocouple installation location far away from the moving coil table, or by dividing number K, N, E, J, T contains copper and nickel materials such as compensating lead wires, the line resistance is bigger, use should pay attention to when choose larger section compensating lead wires. Such as selecting an external 15 Ω line resistance E index number of the moving coil instrument, its with compensating conductor cross-section of 1. 0 mm2、2. 5 was, and the corresponding unit length line resistance 1 respectively. 25 Ω/m and 0. 5 Ω/m, the compensating conductor big for only 12 m and 30 m in length. If you don't pay attention to when designing, the length more than easily, cause measurement error. When thermocouple compensation conductor should be introduced into digital display instrument, if the receiving terminal display device, and display device terminals and instrument between terminals with copper wire connection, due to the difference in temperature will cause measurement error. So good compensation wire across the terminals of the instrument panel will be directly connected to the instrument of the terminals. Such as wiring in the digital display instrument, due to the commonly used in tray display, recorder itself for electricity and heat, make its terminal point temperature is higher than the temperature of the display device terminals.