What is temperature rise test

1. What is a thermocouple?
1.1 Introduction to Thermocouples
Thermocouple (thermocouple) is a temperature measuring element commonly used in temperature measuring instruments. It directly measures the temperature, converts the temperature signal into a thermoelectromotive force signal, and converts it into the temperature of the measured medium through an electrical instrument (secondary instrument). The shape of various thermocouples is often very different due to needs, but their basic structure is roughly the same, usually composed of main parts such as thermode, insulating sleeve protection tube and junction box, usually with display instruments, recording instruments and electronic adjustment used in conjunction with the device.

Thermocouple Applications

In industrial production processes, temperature is one of the important parameters that need to be measured and controlled. In temperature measurement, thermocouples are widely used. They have many advantages, such as simple structure, convenient manufacture, wide measurement range, high precision, small inertia, and easy remote transmission of output signals. In addition, because the thermocouple is a passive sensor, it does not need an external power supply during measurement, and it is very convenient to use, so it is often used to measure the temperature of gas or liquid in furnaces and pipes and the surface temperature of solids.

1.2 Types of Thermocouples
There are eight types of thermocouples: S, R, B, J, K, T, E, N. Among them, R, B, S, are composed of precious metals, and the wire diameter is thin; K, T, E, and N are ordinary metals, and the wire diameter is thick.
Commonly used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. The standard thermocouple referred to refers to the thermocouple whose relationship between thermoelectric potential and temperature, allowable error, and a unified standard graduation table is specified in the national standard. Non-standardized thermocouples are not as good as standardized thermocouples in terms of use range or order of magnitude, and generally do not have a unified indexing table, which is mainly used for measurement in some special occasions.

Standardized thermocouples started since 1st, January, 1988 in our country. All thermocouples and thermal resistances are produced in accordance with IEC international standards, and seven standardized thermocouples of S, B, E, K, R, J, and T are designated as my country’s unified design type thermocouple.

2. Characteristics and applications of standard thermocouples

Thermocouple Types

2.1 Type K thermocouple
K-type thermocouple nickel-chromium (nickel-silicon (nickel-aluminum) thermocouple) K-type thermocouple is a base metal thermocouple with strong oxidation resistance, which can measure the temperature of the medium from 0 to 1300 °C, and is suitable for continuous use in oxidizing and inert gases. The short-term use temperature is 1200 °C, and the long-term use temperature is 1000 °C. The relationship between the thermoelectric potential and the temperature is approximately linear, and it is currently the largest thermocouple. However, it is not suitable for bare wire use in vacuum, sulfur-containing, carbon-containing atmosphere and alternate redox atmosphere; when the oxygen partial pressure is low, the chromium in the nickel-chromium electrode will be preferentially oxidized, which will greatly change the thermoelectric potential , but the metal gas has little effect on it, so metal protection tubes are mostly used.

Disadvantages of K-type thermocouples: (1) The high-temperature stability of thermoelectric potential is worse than that of N-type thermocouples and precious metal thermocouples, and at higher temperatures (for example, over 1000 °C), they are often damaged by oxidation; (2) At 250 ~500 °C the short-term thermal cycle stability in the range is not good, that is, at the same temperature point, in the process of heating and cooling, the thermoelectric potential value is different, and the difference can reach 2 ~ 3 °C; (3) Its negative electrode is at 150 ~ 200 °C Magnetic transition occurs, so that the graduation value in the range from room temperature to 230 °C often deviates from the graduation table, especially when used in a magnetic field, there is often time-independent thermoelectric interference; (4) Long-term high-pass Under the irradiation environment of the system, due to the metamorphism of manganese (Mn), cobalt (Co) and other elements in the negative electrode, its stability is not good, resulting in a large change in thermoelectric potential.

2.2 S-type thermocouple
S-type thermocouple (platinum-rhodium 10-platinum thermocouple) The positive electrode of the thermocouple is a platinum-rhodium alloy containing 10% rhodium, and the negative electrode is pure platinum. Its characteristics are: (1) stable thermoelectric performance, strong oxidation resistance, suitable for continuous use in an oxidizing atmosphere, long-term use temperature up to 1300 ℃, when it exceeds 1400 ℃, even in the air, pure platinum wire will also recrystallization makes the grains coarse and fractured; (2) High precision, the highest level of accuracy among all thermocouples, usually used as a standard or to measure higher temperatures; (3) Wide range of use, uniformity and interchangeability Good; (4) The main disadvantages are: the differential thermoelectric potential is small, so the sensitivity is low; the price is more expensive, the mechanical strength is low, and it is not suitable for use in a reducing atmosphere or under the conditions of metal vapor.

2.3 Type E thermocouple
E-type thermocouple (nickel-chromium-copper-nickel [constantan] thermocouple) E-type thermocouple is a relatively new product, the positive electrode is a nickel-chromium alloy, and the negative electrode is a copper-nickel alloy (constantan). Its biggest feature is that among the commonly used thermocouples, its thermoelectric potential is the largest, that is, the sensitivity is the highest; although its application range is not as wide as that of K-type couples, it requires high sensitivity, low thermal conductivity, and large resistance. The limitations in use are the same as the K type, but are less sensitive to corrosion in atmospheres containing higher humidity.

2.4 N-type thermocouple
N-type thermocouple (nickel-chromium-silicon-nickel-silicon thermocouple) The main features of this thermocouple: strong anti-oxidation ability in temperature regulation below 1300 ℃, good long-term stability and short-term thermal cycle repeatability, resistance to nuclear radiation and low temperature good performance. In addition, in the range of 400 ~ 1300 ° C, the linearity of the thermoelectric characteristics of the N type thermocouple is better than that of the K type.

2.5 J-type thermocouple
J-type thermocouple (iron-constantan thermocouple) J-type thermocouple: the positive electrode of the thermocouple is pure iron, and the negative electrode is constantan (copper-nickel alloy). In the atmosphere, the temperature ranges from -200 to 800 °C, but the commonly used temperature is only below 500 °C, because the oxidation rate of the iron hot electrode is accelerated after this temperature is exceeded. And has a long life; the thermocouple is resistant to hydrogen (H2) and carbon monoxide (CO) gas corrosion, but cannot be used in a high temperature (such as 500 ° C) atmosphere containing sulfur (S).

2.6 T-type thermocouple
T-type thermocouple (copper-copper-nickel thermocouple) T-type thermocouple: the positive electrode of the thermocouple is pure copper, and the negative electrode is copper-nickel alloy (also called constantan). Its main features are: in the base metal thermocouple , it has the highest accuracy and good uniformity of the hot electrode; its operating temperature is -200 ~ 350 ° C, because the copper hot electrode is easy to oxidize, and the oxide film is easy to fall off, so when used in an oxidizing atmosphere, generally can not exceed 300 ℃, in the range of -200 ~ 300 ℃, their sensitivity is relatively high. Another feature of copper-constantan thermocouples is that they are cheap, which is the cheapest one of several commonly used stereotypes.

2.7 R-type thermocouple
R-type thermocouple (platinum-rhodium 13-platinum thermocouple) The positive electrode of the thermocouple is a platinum-rhodium alloy containing 13%, and the negative electrode is pure platinum. Compared with the S-type, its potential rate is about 15% larger, and other properties are almost Similarly, this kind of thermocouple is used the most as a high-temperature thermocouple in the Japanese industry, but it is used less in China.

3. What factors should be considered when choosing a thermocouple and what to pay attention to
3.1 Factors to Consider When Selecting Thermocouples
• Measured temperature range
• Required response time
• Connection point type
• Chemical resistance of thermocouple or sheath material
• Resistance to wear or vibration
• Installation and restriction requirements, etc.

3.2 Precautions for use
• The correct wiring method of the thermocouple of the temperature tester is: the red wire is connected to the negative pole, and the white wire is connected to the positive pole. When connecting, the two strands must be pushed up to the triangle of the male plug to prevent the exposed part from short-circuiting.
• When the thermocouple of the temperature tester is attached to the workpiece, it must be remembered to closely fit the product workpiece, and the solder joint of the thermocouple cannot be shaken inside, especially when the thermocouple solder joint touches the metal, it is easy to generate instantaneous voltage , and the temperature in the measured temperature curve suddenly rises very high, which will cause the Y-axis coordinate of the analysis software to become very high, so the whole curve will look very small.
• When using the thermocouple of the temperature tester, do not tie a knot or fold it to more than 90 degrees. This will easily cause the two inner cores to break. After breaking, you do not know where it broke, then this thermocouple will be broken. Be careful when using it, and don’t use it brutally.
• Remember to use a thermocouple welder to weld the thermocouple wire connections after the solder joints are disconnected. Instead of using something else to solder them.

4. LISUN Solution
8 channels temperature signal (TMP-8) or 16 channels temperature signal (TMP-16). K type thermocouple Sensors. Temperature range: -40~300℃ and testing accuracy: Class 0.5. Capable of circle monitoring, single monitoring, printing and communication with PC.

TMP-8/TMP-16_Multiplex Temperature Tester

The TMP-L Lamp Cap Temperature Rise Test System is according to IEC60360, GB2512 (Standard method of measurement of lamp cap temperature rise), IEC60598 and GB7000.1. It is used to test the working and environmental temperature as well as temperature-rise of the burner and lamp. K type thermocouple Sensors. Temperature range: -40~300℃ and testing accuracy: Class 0.5. Capable of circle monitoring, single monitoring, printing and communication with PC.

TMP L_Lamp Cap Temperature Rise Test System

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