What type of thermocouple for industrial electric furnace?

1. Re-explicit - with the same two thermocouple materials thermocouple, requiring their electric properties of the phase and stable, so that the thermocouple can be mass production, and a good interchangeability;

2. High sensitivity, good linearity - the thermocouple potential of the thermocouple is required to be large enough and linearly related to temperature;

3. High temperature-thermocouple temperature range depends mainly on the high temperature performance of the hot electrode, that is, in the high temperature medium, the thermal electrode of the physical and chemical properties of the more stable, the composition of the thermocouple temperature range The wider.

Tubular resistance furnace electric furnace with thermocouple, should be used in accordance with the requirements of a reasonable choice. Currently used thermocouples are the following:

1, nickel chrome / test copper thermocouple - text index number E, positive nickel chromium composition of 9-10% chromium, 0.4% silicon, the rest of the nickel; negative copper test porcelain is divided into 56% copper and 44% nickel.

The biggest advantage of this galvanic is the thermoelectric power, cheap. The shortcomings of this thermocouple can not be used to measure high temperature, the temperature limit of 800 ℃, long-term use, only 600 ℃ below, in addition, due to copper alloy susceptible to oxidation and deterioration, the use of protective cover must be installed tube.

2, copper / Kang copper thermocouple - its index number T, the cathode is copper, the negative 60% copper / 40% nickel alloy.

The advantages of this galvanic temperature sensitivity is higher, easy to copy the hot electrode, cheap, low temperature performance, measurable -200 ℃ low temperature. But the composition of copper easy to oxidation, so the general temperature limit does not exceed 300 ℃.

3, nickel chrome / nickel silicon thermocouple - its sub-number K, the positive component is 9-10% chromium, 0.4% silicon, the rest is nickel, the negative component of 2.5-3% silicon, <0.6% chromium, the rest For nickel.

The advantages of this type of thermocouple is a strong antioxidant and corrosion resistance, other good stability, thermal potential, thermoelectric potential and temperature of the linear relationship between the good, box-type resistance furnace price of its thermal electrode material Cheap, can be used continuously below 1000 ℃, short-term temperature measurement up to 1300 ℃.

The drawback is that it is easy to be corroded at a temperature above 500 ° C and in a reducing medium and in the use of sulfur and a chemical atmosphere. Therefore, it is necessary to apply a protective sleeve when working in these atmospheres, Temperature accuracy is also lower than platinum rhodium / platinum thermocouple.

4, platinum and rhodium / platinum thermocouple - its index number S, the positive electrode is 90% platinum and 10% rhodium alloy, the cathode is pure platinum wire.

Platinum rhodium / platinum thermocouple has the advantage of being easy to prepare pure platinum rhodium alloy, so easy to copy, and high temperature accuracy, can be used as the international practical temperature scale 630.74-1064.43 ℃ range of the reference thermocouple.

Its high physical and chemical stability, should be used in oxidizing and neutral atmosphere; its melting point is high, so the temperature limit is also high. In industrial measurement generally use it to measure the temperature above 1000 ℃, 1300 ℃ in the following long-term continuous use, short-term temperature up to 1600 ℃.

Platinum rhodium / platinum thermocouple shortcomings are expensive, thermoelectric power is small, in the reducing gas, metal vapor, metal oxides and silicon oxide and sulfur oxide and other atmosphere will soon be subject to contamination and deterioration, so in these The use of it in the atmosphere to protect the casing, in addition, the thermoelectric properties of this thermocouple non-linear, at high temperatures, the thermal electrode will sublimate, so that rhodium molecules penetrate into the platinum to stain it, resulting in thermoelectric Unstable.

5, platinum and rhodium 30 / platinum and rhodium 6 thermocouple - referred to as double platinum and rhodium thermocouple, sub-degree number B. The positive and negative poles of the thermocouple are platinum and rhodium alloy, only the proportion of the alloy is different, the positive rhodium 30%, the negative rhodium is 6%, double platinum and rhodium thermocouple anti-pollution ability, 1800 ℃ temperature is still very good stability. Its high temperature accuracy, suitable for oxidation, neutral medium, long-term continuous measurement of 1400-1600 ℃ high temperature, short-term measurement up to 1800 ℃.

Double platinum and rhodium thermocouple sensitivity is low, use should be equipped with high sensitivity display instrument. Vacuum atmosphere furnace temperature at room temperature on the thermal potential of the impact of minimal, so the general use of temperature compensation is not required.