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Thermal Resistance And Thermocouple Related Performance And Selection Reference
Dec 24, 2018

Thermal resistance and thermocouple related performance and selection reference


The temperature meter is an important meter for temperature detection. The structure is various, and different types of products are suitable for different working conditions. Users should clearly understand the performance of different components when selecting the type to ensure that the selected products meet the temperature measurement requirements of the working environment. Today, Huaheng Instrument will give you a detailed introduction to the relevant performance of the thermal resistance and thermocouple for reference selection.

Thermal resistance and thermocouple related performance and selection reference

Temperature meter classification

There are many classification methods for temperature instruments. According to the temperature measurement method, they can be divided into two types: contact type and non-contact type. According to the application, they can be divided into reference thermometers and industrial thermometers. According to the different temperature assembly methods, they are divided into assembly and armor. According to the explosion-proof performance, it is divided into explosion-proof and waterproof. At present, the temperature instruments used in industrial production mainly include thermal resistance, thermocouple, industrial bimetal thermometer and temperature transmitter. Among them, thermistor and thermocouple are also called temperature sensors, which is a contact measurement. The instrument is usually matched with its corresponding display, recording and adjustment instrument, or used with the temperature transmitter and industrial control system.

Thermal resistance

The thermal resistance is a temperature sensor that uses a resistance as a function of temperature, and the output signal is an ohmic value. According to different thermal resistance temperature measuring components, it is divided into copper thermal resistance and platinum thermal resistance. At present, the thermal resistance indexing numbers used in industry mainly include Cu100, Cu50, Pt10, Pt100 and so on.

 

Industrial copper thermal resistance (Cu100, Cu50)

Performance and technical indicators

Scope of application

Industrial copper thermal resistors are widely used to measure temperatures in the range of 50 to 150 °C. The advantages are: high-purity copper wire is easy to obtain; copper has a large temperature coefficient of resistance; the price is cheap and the interchangeability is good. Chemical, textile and other industries are in great use.

 

Industrial Platinum Thermal Resistance (Pt10, Pt100)

Performance and technical indicators

Scope of application

Industrial platinum thermal resistors are widely used to measure temperatures in the range of 200-550 °C. The standard platinum resistance thermometer has the highest accuracy and can be used as a standard thermometer for interpolation below 961.78 °C in the international temperature standard. Compared with thermocouples, it has the advantages of high accuracy, large output signal, high sensitivity and good stability.

 

Based on the above information, the copper thermal resistance has low precision and a small measurement range, which is much lower than the platinum resistance. Platinum thermal resistance has high precision and high temperature range, and is used in temperature measurement in industrial production processes below 550 °C. Under normal circumstances, when the secondary instrument receives the signal as an ohmic signal, the thermal resistance sensor must be selected. The specific index number should be considered comprehensively considering the system design, system measurement accuracy and measurement range.


Thermal resistance and thermocouple related performance and selection reference

Thermocouple

The thermocouple is connected by conductors A and B of two different compositions to form a closed loop. When the temperature of the cold end and the hot end are different, an electromotive force is generated in the loop. The output signal of the thermocouple is a millivolt value. At present, there are many types of thermocouples at home and abroad, which are mainly divided into two categories: low-cost metal thermocouples and precious metal thermocouples. The following describes the relevant properties of commonly used thermocouples in several industrial processes.

 

Nickel-chromium-nickel-silicon (K-index) thermocouple

Nickel-chromium-nickel-silicon thermocouples are among the best-performing products in the current styling products, and are suitable for temperature measurement in an oxidizing or inert atmosphere in the range of 200 ° C to 800 ° C.

Its advantages:

1. The relationship between the thermoelectric potential and the temperature is approximately linear, so that the scale of the display instrument is uniform;

2. Good stability and uniformity;

3. Antioxidant performance is better than other inexpensive metal thermocouples. Such products are not suitable for use in reducing atmospheres or alternately oxidizing and reducing atmospheres unless protected with a suitable protective tube; in a sulfur-containing atmosphere, unless properly protected; in a vacuum atmosphere.

Copper-Constantan (T-division) thermocouple

The copper-constantan thermocouple is corrosion-resistant in a humid atmosphere. It is suitable for measurement of negative temperature and has an upper limit of 400 ° C for vacuum, oxidation and reduction or inert atmosphere. The performance of such products is stable, especially in a stable temperature of 200 ~ 0 ° C, the value of the change in a year or so is ± 3 microvolts, copper-constantan thermocouple also has a characteristic is cheap, is several The cheapest one of the stereotyped products.


Thermal resistance and thermocouple related performance and selection reference

Platinum crucible Platinum (s indexing) thermocouple

Platinum 铑10-platinum thermocouple with high temperature resistance of 1300 °C, has many characteristics: high precision; good physical and chemical properties; good oxidation resistance at high temperature, suitable for oxidizing and inert atmosphere. The disadvantages are as follows: compared with the previous several types of thermocouples, the differential thermoelectric potential is small and the sensitivity is low. It is necessary to select a more precise display instrument to ensure accurate measurement results; it is a precious metal material and has a high price.

Platinum rhodium 30-platinum rhodium 6 (B indexing) thermocouple

Platinum rhodium 30-platinum rhodium 6 thermocouple can be said to be an ideal temperature gauge for measuring high temperature. It is suitable for continuous use in oxidizing and inert atmosphere at a temperature of 0 ° C - 1800 ° C, and can also be used in vacuum for a short time. In the atmosphere. The platinum-iridium 10-platinum thermocouple has all the advantages, and its measurement temperature range is currently the highest in the stereotyped product.

The above details the performance of several thermocouples commonly used in industrial measurement, thermal resistance and thermocouple related performance and selection reference. In actual use, the user has other thermocouples with different indexing numbers to choose from.