【Daily Question】20150813
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0–1800°C, or the deviation from 1600°C is unknown
What is the measurement range and the allowable deviation for the second stage of S-type thermocouples? Thermocouples are one of the most commonly used temperature sensing elements in industry. Their advantages are as follows: 1. High measurement accuracy. Since thermocouples come into direct contact with the object being measured, they are not affected by intermediate media. 2. Wide measurement range. Commonly used thermocouples can continuously measure temperatures from -50 to +1600°C; some special types can measure as low as -269°C (such as those made of gold, iron, nickel, and chromium) and as high as +2800°C (such as tungsten-rhenium types). 3. Simple structure and easy to use. Thermocouples usually consist of two different metal wires, and there are no restrictions regarding their size or shape. They also have a protective sleeve, making them very convenient to use.
I. Basic Principle of Thermocouple Temperature Measurement
When two conductors or semiconductors of different materials, A and B, are welded together to form a closed circuit, as shown in Figure 2-1-1, an electromotive force is generated between points 1 and 2 where these two conductors meet, if there is a temperature difference between them. This results in an electric current flowing in the circuit. This phenomenon is known as the thermoelectric effect. Thermocouples operate by taking advantage of this effect.
II. Types and Structures of Thermocouples
1. Types of Thermocouples
Commonly used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. Standard thermocouples are those for which standards specify the relationship between their thermoelectromotive force and temperature, as well as allowable errors, along with standardized calibration tables. There are also corresponding measuring instruments available for use with them. Non-standard thermocouples have a narrower range of applications and lower precision compared to standard thermocouples; they generally do not have standardized calibration tables either. They are mainly used for measurements in special situations. In China, since January 1, 1988, all thermocouples and thermal resistors have been manufactured in accordance with IEC international standards. Seven standard thermocouple types—S, B, E, K, R, J, and T—have been designated as the standard types for use in China.
2. Structural Forms of Thermocouples
To ensure reliable and stable operation of thermocouples, the following structural requirements must be met: A. The welding of the two thermoelectrodes that make up the thermocouple must be secure. B. The two thermoelectrodes must be properly insulated from each other to prevent short circuits. C. The connection between the compensation wire and the free end of the thermocouple must be convenient and reliable. D. The protective sleeve must ensure that the thermoelectrodes are fully isolated from harmful substances.
III. Temperature Compensation for the Cold End of Thermocouples
Since the materials used in thermocouples are usually expensive (especially when precious metals are used), and the distance between the measurement point and the instrument is often large, compensation wires are used to extend the cold end (free end) of the thermocouple to a control room where the temperature is more stable, thereby connecting it to the instrument terminals. It should be noted that the function of the compensation wire is merely to extend the thermoelectrodes and move the cold end to the instrument terminals in the control room. It does not eliminate the impact of changes in the cold end temperature on temperature measurement; therefore, other correction methods are needed to compensate for such effects when the cold end temperature is not at 0°C. When using compensation wires, it is important to ensure that the correct type is used, that the polarity is not reversed, and that the temperature at the connection point between the compensation wire and the thermocouple does not exceed 100°C.
I. Basic Principle of Thermocouple Temperature Measurement
When two conductors or semiconductors of different materials, A and B, are welded together to form a closed circuit, as shown in Figure 2-1-1, an electromotive force is generated between points 1 and 2 where these two conductors meet, if there is a temperature difference between them. This results in an electric current flowing in the circuit. This phenomenon is known as the thermoelectric effect. Thermocouples operate by taking advantage of this effect.
II. Types and Structures of Thermocouples
1. Types of Thermocouples
Commonly used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. Standard thermocouples are those for which standards specify the relationship between their thermoelectromotive force and temperature, as well as allowable errors, along with standardized calibration tables. There are also corresponding measuring instruments available for use with them. Non-standard thermocouples have a narrower range of applications and lower precision compared to standard thermocouples; they generally do not have standardized calibration tables either. They are mainly used for measurements in special situations. In China, since January 1, 1988, all thermocouples and thermal resistors have been manufactured in accordance with IEC international standards. Seven standard thermocouple types—S, B, E, K, R, J, and T—have been designated as the standard types for use in China.
2. Structural Forms of Thermocouples
To ensure reliable and stable operation of thermocouples, the following structural requirements must be met: A. The welding of the two thermoelectrodes that make up the thermocouple must be secure. B. The two thermoelectrodes must be properly insulated from each other to prevent short circuits. C. The connection between the compensation wire and the free end of the thermocouple must be convenient and reliable. D. The protective sleeve must ensure that the thermoelectrodes are fully isolated from harmful substances.
III. Temperature Compensation for the Cold End of Thermocouples
Since the materials used in thermocouples are usually expensive (especially when precious metals are used), and the distance between the measurement point and the instrument is often large, compensation wires are used to extend the cold end (free end) of the thermocouple to a control room where the temperature is more stable, thereby connecting it to the instrument terminals. It should be noted that the function of the compensation wire is merely to extend the thermoelectrodes and move the cold end to the instrument terminals in the control room. It does not eliminate the impact of changes in the cold end temperature on temperature measurement; therefore, other correction methods are needed to compensate for such effects when the cold end temperature is not at 0°C. When using compensation wires, it is important to ensure that the correct type is used, that the polarity is not reversed, and that the temperature at the connection point between the compensation wire and the thermocouple does not exceed 100°C.
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For S-type type 1 thermocouples, the allowable error is 4‰; for type 2 thermocouples, it is 8‰. The measurement range for long-term use is 0-1300, while for short-term use it is 0-1800. The calculated allowable deviation is 10.4 ℃
The answer is set to hidden. . . What is the measurement range and the allowable deviation for the second stage of S-type thermocouples? Measurement range: 0–1600℃ Allowable deviation: ±0.25%t
The title itself is the problem; please take a look.
The diameter of the odd filaments is specified as 0.5 mm, with a permissible deviation of -0.015 mm
Temperature measurement range: °C 0~1600; generally, it should not exceed 1300. The allowable deviation is probably 0.25%
What is the measurement range and the allowable deviation for the second stage of S-type thermocouples? The maximum long-term operating temperature is 1300°C, and the maximum short-term operating temperature is 1600°C. Basic error limit ±0.25%t