[Daily question 20090301] Types of thermometers

High expansion alloys are expansion alloys whose linear expansion coefficient is higher than 16x10--zhou ℃. It is widely used as a temperature measuring element in the field of engineering technology. High-expansion alloys are rarely used alone, and are almost always paired with low-expansion alloy components to form thermal bimetals. Therefore, this alloy must have a high expansion coefficient; can be firmly combined with low-expansion alloys; have good heat resistance and ductility; be easy to make plates and strips with uniform properties; have a certain resistance value; and have little difference in elastic modulus from low-expansion alloy components to facilitate deformation processing. In addition, the chemical composition affects the linear expansion coefficient and resistivity of high-expansion alloys. The linear expansion coefficients (20-100oC) of commonly used high-expansion alloys are: Cu60 Zn 40 is 19 x 10-6/℃, FeNi 22 Cr3 is 18.sx-0-6/oC, FeNi20Mn6 and FeNi 13 Mn7 are 21 x 10-6/oC, Mn 72 Cr 18 Ni 10 is 26 x 10-6/℃. The smelting and processing techniques of iron-nickel-chromium and iron-nickel-manganese high-expansion alloys are similar to those of iron-nickel low-expansion alloys. The smelting and processing technology of manganese-nickel-copper high-expansion alloy is complex and must be operated strictly. For example, if non-vacuum smelting is used, the slag must be removed when tapping to avoid cracking during forging. The starting forging temperature is 870°C, and the stopping temperature shall not be lower than 650°C. Thermocouple - The main text is a temperature sensing element made of two conductors of different materials connected together, which can produce a thermoelectric effect, also known as a thermocouple. It is a thermoelectric temperature sensor. The output signal is the temperature difference potential, which can be directly sent to the display instrument to indicate the temperature value of the measured object. Therefore it is classified as a temperature measuring instrument. The advantage of the thermocouple is that it has a wide measuring range (-200~1600℃), is convenient for long-distance measurement, has high accuracy, does not require an external power supply, has a simple structure, is easy to use, and can adapt to various requirements (small size, fast and point temperature measurement), and is a commonly used temperature measurement element. 　　In Figure b, when there is a temperature difference between the two contacts 1 and 2 of conductors A and B, a thermoelectric potential is generated in the loop. This physical effect is called the thermoelectric effect. The thermoelectric effect was discovered by German physicist TJ Seebeck in 1821, so it is also called the Seebeck effect. One end of the temperature sensing element of the thermocouple has conductors A and B welded together (Figure a), which is called the measuring end and is placed in the measured medium with a temperature of t ； The other end is called the reference end and is at a constant temperature t0. When the temperature at the measuring end changes, the temperature difference potential changes accordingly, and the value of t can be read on the display instrument. The material at the measuring end is required to have stable physical and chemical properties, small resistance temperature coefficient, high conductivity, and large temperature difference potential at both ends. According to the different materials of the measuring end, thermocouples are divided into refractory metal thermocouples (such as tungsten rhenium 5 - tungsten rhenium 20, etc.), precious metal thermocouples (such as platinum rhodium 10 - platinum, iridium rhodium 1 0-iridium, etc.), cheap metal thermocouples (such as iron-constantan, nickel-chromium-copper, etc.), non-metal thermocouples (such as tungsten carbide-molybdenum carbide, graphite-silicon carbide, etc.). The structural forms of thermocouples are divided into four types according to different uses. ①Ordinary thermocouple: mostly used in industry. ②Armored thermocouple: small thermal inertia, fast dynamic response, time constant up to 0.01 seconds, good flexibility, and good earthquake resistance. ③Thin film thermocouple: Used for rapid measurement of wall temperature, the temperature measurement range is below 300°C, and the response time is a few milliseconds. ④Consumable thermocouple: a thermocouple for measuring the temperature of molten steel. It is incinerated after one use. The advantage is that it has small thermal inertia. 　　During actual temperature measurement, the thermocouple and protective sleeve are selected based on the temperature, pressure, properties, and temperature measurement time of the medium to be measured. A device that can measure one or several meteorological elements (such as air pressure, temperature, humidity, etc.) at each altitude as the weather balloon rises (or is dropped by a fixed-altitude balloon, airplane, rocket, etc.) and a radio transmitter that sends the resulting information, referred to as a radiosonde. It was developed in the late 1920s based on high-altitude weather instruments and radio shortwave technology. Because the instrument is compact, the observation method is simple, and the detection results are timely and reliable, and the altitude can generally reach 30 kilometers, it has quickly become the main tool for high-altitude weather observation. Promoted the establishment of the world's high-altitude meteorological station network. Since the sounding balloon can rise to an altitude of about 30 kilometers, the detection range of meteorological elements by the sounding instrument should be respectively: The temperature is 40~-90°C, the air pressure is 1060~5 hPa, and the relative humidity is 100~0%. And the induction needs to be fast. According to weather analysis requirements, the general accuracy of the radiosonde: The air temperature is ±0.5°C, the air pressure is ±1 hPa, and the relative humidity is ±5%. 　　Working Principle A radiosonde consists of a sensing element, a transfer switch, an encoder, a radio transmitter and a power supply. The temperature, pressure and humidity at each altitude of the atmosphere are sensed by temperature, pressure and humidity components respectively. The mechanical or electrical output is sequentially connected to the encoder by the conversion switch and converted into electrical signals, which are then sent by the transmitter through amplitude modulation or frequency modulation, and are received, demodulated and recorded on the ground. The recording and sorting of data is gradually moving from manual to fully automated (see picture). 　　Types Radiosondes used in various countries can be divided into three categories: electrical code type, time type and frequency type according to the coding method. Frequency type can be divided into two types: high frequency type and low frequency type. Chinese-made radiosondes use two types: telegraph type and low frequency type. 　　Development Trend Since the 1960s, various countries have made a series of improvements to radiosondes: The pressure measuring element has empty boxes with different ranges suitable for high-altitude and low-altitude use (see ground meteorological observation instruments). The material of the empty box has been changed from phosphor bronze to nickel-chromium titanium. There are many temperature measuring components * * The surface is coated with a high-reflectivity coating to produce a rod-shaped thermistor with a diameter of only about 1 mm. In addition, there is a more expensive standard temperature sonde that uses 13-20 micron thin metal wires as temperature measurement elements to improve the temperature measurement accuracy of conventional radiosondes through comparative emission. On the basis of conventional radiosondes, a variety of special radiosondes are derived based on different detection purposes (such as measuring ozone, stratospheric dew point, various radiation fluxes, atmospheric electric fields, monitoring low-level atmospheric pollution, etc.) or different instrument deployment methods (such as up and down drops from aircraft, weather rockets, translational carrier balloons). They often use their special names to indicate their special uses, such as ozone sondes, etc. This post was last written by wwxxss_1 edited on 2009-3-1 14:21 ]

Thermocouple - A temperature sensing element made of two conductors of different materials connected together and capable of producing a thermoelectric effect, also known as a thermocouple. It is a thermoelectric temperature sensor. The output signal is the temperature difference potential, which can be directly sent to the display instrument to indicate the temperature value of the measured object. Therefore it is classified as a temperature measuring instrument. The advantage of the thermocouple is that it has a wide measuring range (-200~1600℃), is convenient for long-distance measurement, has high accuracy, does not require an external power supply, has a simple structure, is easy to use, and can adapt to various requirements (small size, fast and point temperature measurement), and is a commonly used temperature measurement element. 　　In Figure b, when there is a temperature difference between the two contacts 1 and 2 of conductors A and B, a thermoelectric potential is generated in the loop. This physical effect is called the thermoelectric effect. The thermoelectric effect was discovered by German physicist TJ Seebeck in 1821, so it is also called the Seebeck effect. One end of the temperature sensing element of the thermocouple has conductors A and B welded together (Figure a), which is called the measuring end and is placed in the measured medium with a temperature of t ； The other end is called the reference end and is at a constant temperature t0. When the temperature at the measuring end changes, the temperature difference potential changes accordingly, and the value of t can be read on the display instrument. The material at the measuring end is required to have stable physical and chemical properties, small resistance temperature coefficient, high conductivity, and large temperature difference potential at both ends. According to the different materials of the measuring end, thermocouples are divided into refractory metal thermocouples (such as tungsten rhenium 5 - tungsten rhenium 20, etc.), precious metal thermocouples (such as platinum rhodium 10 - platinum, iridium rhodium 1 0-iridium, etc.), cheap metal thermocouples (such as iron-constantan, nickel-chromium-copper, etc.), non-metal thermocouples (such as tungsten carbide-molybdenum carbide, graphite-silicon carbide, etc.). The structural forms of thermocouples are divided into four types according to different uses. ①Ordinary thermocouple: mostly used in industry. ②Armored thermocouple: small thermal inertia, fast dynamic response, time constant up to 0.01 seconds, good flexibility, and good earthquake resistance. ③Thin film thermocouple: Used for rapid measurement of wall temperature, the temperature measurement range is below 300°C, and the response time is a few milliseconds. ④Consumable thermocouple: a thermocouple for measuring the temperature of molten steel. It is incinerated after one use. The advantage is that it has small thermal inertia. 　　During actual temperature measurement, the thermocouple and protective sleeve are selected based on the temperature, pressure, properties, and temperature measurement time of the medium to be measured.

A device that can measure one or several meteorological elements (such as air pressure, temperature, humidity, etc.) at each altitude as the weather balloon rises (or is dropped by a fixed-altitude balloon, airplane, rocket, etc.) and a radio transmitter that sends the resulting information, referred to as a radiosonde. It was developed in the late 1920s based on high-altitude weather instruments and radio shortwave technology. Because the instrument is compact, the observation method is simple, and the detection results are timely and reliable, and the altitude can generally reach 30 kilometers, it has quickly become the main tool for high-altitude weather observation. Promoted the establishment of the world's high-altitude meteorological station network. Since the sounding balloon can rise to an altitude of about 30 kilometers, the detection range of meteorological elements by the sounding instrument should be respectively: The temperature is 40~-90°C, the air pressure is 1060~5 hPa, and the relative humidity is 100~0%. And the induction needs to be fast. According to weather analysis requirements, the general accuracy of the radiosonde: The air temperature is ±0.5°C, the air pressure is ±1 hPa, and the relative humidity is ±5%. 　　Working Principle A radiosonde consists of a sensing element, a transfer switch, an encoder, a radio transmitter and a power supply. The temperature, pressure and humidity at each altitude of the atmosphere are sensed by temperature, pressure and humidity components respectively. The mechanical or electrical output is sequentially connected to the encoder by the conversion switch and converted into electrical signals, which are then sent by the transmitter through amplitude modulation or frequency modulation, and are received, demodulated and recorded on the ground. The recording and sorting of data is gradually moving from manual to fully automated (see picture). 　　Types Radiosondes used in various countries can be divided into three categories: electrical code type, time type and frequency type according to the coding method. Frequency type can be divided into two types: high frequency type and low frequency type. Chinese-made radiosondes use two types: telegraph type and low frequency type. 　　Development Trend Since the 1960s, various countries have made a series of improvements to radiosondes: The pressure measuring element has empty boxes with different ranges suitable for high-altitude and low-altitude use (see ground meteorological observation instruments). The material of the empty box has been changed from phosphor bronze to nickel-chromium titanium. There are many temperature measuring components * * The surface is coated with a high-reflectivity coating to produce a rod-shaped thermistor with a diameter of only about 1 mm. In addition, there is a more expensive standard temperature sonde that uses 13-20 micron thin metal wires as temperature measurement elements to improve the temperature measurement accuracy of conventional radiosondes through comparative emission. On the basis of conventional radiosondes, a variety of special radiosondes are derived based on different detection purposes (such as measuring ozone, stratospheric dew point, various radiation fluxes, atmospheric electric fields, monitoring low-level atmospheric pollution, etc.) or different instrument deployment methods (such as up and down drops from aircraft, weather rockets, translational carrier balloons). They often use their special names to indicate their special uses, such as ozone sondes, etc.

glass thermometer: Liquid expands in volume when heated ； -100~600℃, cheap, high precision, good stability, easy to damage, can only be installed in places where it is easy to observe. Bimetal thermometer: Metal expands linearly when heated ； -50~600℃, clear indication, good mechanical strength, low accuracy pressure thermometer: The gas or liquid in the temperature bulb changes pressure due to heating ； -50~600℃, cheap and easiest to detect on site. The mechanical strength of the capillary is poor and it is difficult to repair the thermal resistance thermometer after damage.: The resistance of a conductor or semiconductor changes with temperature ； -200~600℃, accurate measurement, can be used for low temperature or low temperature difference measurement. Compared with thermocouples, the maintenance workload is large, and the thermocouple thermometer is easily damaged in vibration situations.: The junction of two different metal conductors generates thermoelectric potential when heated ； -50~1600℃ Accurate measurement, easier to install and maintain than thermal resistors, not easily damaged, requires compensation wires, higher installation costs Optical pyrometer: The brightness of the heating body changes with the temperature, 700 to 3200°C. It has a wide temperature measurement range, is easy to carry and use, and is cheap. It can only be measured visually, and you must be skilled to measure more accurate data. Photoelectric pyrometer: The color of the heating body changes with the temperature. 50~2000℃ has fast response speed, more accurate measurement, complex structure, high price, and troublesome reading. Radiation pyrometer: The radiant energy of the heating body changes with the temperature, 50~2000℃, the reaction speed is fast and the error is large.

Thermocouples are one of the most commonly used temperature sensing components in industry. The advantage is: ①High measurement accuracy. Because the thermocouple is in direct contact with the measured object, it is not affected by the intermediate medium. ②Wide measuring range. Commonly used thermocouples can continuously measure from -50 to +1600°C. Some special thermocouples can measure as low as -269°C (such as gold, iron, nickel and chromium) and as high as +2800°C (such as tungsten-rhenium). ③The structure is simple and easy to use. Thermocouples are usually composed of two different metal wires, and are not limited by size or opening. They have protective sleeves on the outside, making them very convenient to use. 1． The basic principle of thermocouple temperature measurement is to weld two conductors or semiconductors A and B of different materials to form a closed loop. When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, an electromotive force is generated between the two, thus forming a large current in the loop. This phenomenon is called the thermoelectric effect. Thermocouples take advantage of this effect to work. 2． Types and structural formation of thermocouples (1) Types of thermocouples Commonly used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. The standard thermocouple referred to is * * The standard stipulates the relationship between thermoelectric potential and temperature, the allowable error, and a thermocouple with a unified standard scale. It has a matching display instrument for selection. Non-standardized thermocouples are not as good as standardized thermocouples in terms of use range or order of magnitude. They generally do not have a unified graduation table and are mainly used for measurements in certain special occasions. Standardized Thermocouples In my country, since January 1, 1988, all thermocouples and thermal resistors have been produced in accordance with IEC international standards, and seven types of standardized thermocouples, S, B, E, K, R, J, and T (i.e., graduation numbers), have been designated as unified design thermocouples in my country. (2) Structural form of thermocouple In order to ensure that the thermocouple works reliably and stably, its structural requirements are as follows: ① The two hot electrodes that make up the thermocouple must be welded firmly ② The two hot electrodes should be well insulated from each other to prevent short circuits ③ The connection between the compensation wire and the free end of the thermocouple must be convenient and reliable ④ The protective sleeve should be able to ensure that the hot electrodes are fully isolated from harmful media 3. Temperature compensation of thermocouple cold end Since thermocouple materials are generally relatively expensive (especially when using precious metals), and the distance between the temperature measurement point and the instrument is very long, in order to save thermocouple materials and reduce costs, compensation wires are usually used to extend the cold end (free end) of the thermocouple to the control room where the temperature is relatively stable, and connect it to the instrument terminals. It must be pointed out that the thermocouple compensation wire only functions to extend the hot electrode and move the cold end of the thermocouple to the instrument terminal in the control room. It itself cannot eliminate the influence of the cold end temperature change on the temperature measurement and has no compensation effect. Therefore, other correction methods need to be used to compensate for the impact on temperature measurement when the cold end temperature t0≠0℃. When using the thermocouple compensation wire, you must pay attention to the matching model, the polarity cannot be wrong, and the temperature of the compensation wire and the thermocouple connection end cannot exceed 100°C. For example: S-type thermocouple) Platinum-rhodium 10-platinum thermocouple Platinum-rhodium 10-platinum thermocouple (S-type thermocouple) is a precious metal thermocouple. The diameter of the coupler wire is specified as 0.5mm, and the allowable deviation is -0.02mm. The nominal chemical composition of the positive electrode (SP) is a platinum-rhodium alloy, which contains 10% rhodium and 90% platinum. The negative electrode (SN) is pure platinum, so it is commonly known as a single platinum-rhodium thermocouple. The maximum long-term use temperature of this thermocouple is 1300°C, and the short-term maximum use temperature is 1600°C. The S-type thermocouple has the advantages of highest accuracy, best stability, wide temperature measurement range, and long service life among the thermocouple series. It has good physical and chemical properties, good thermoelectric potential stability and good oxidation resistance at high temperatures, and is suitable for use in oxidizing and inert atmospheres. Because the S-type thermocouple has excellent comprehensive performance and conforms to the international temperature scale, it has long been used as an interpolation instrument for the international temperature scale. Although "ITS-90" stipulates that it will no longer be used as an interpolation instrument for the international temperature scale in the future, the International Temperature Consultative Committee (CCT) believes that the S-type thermocouple can still be used to approximately implement the international temperature scale. The shortcomings of the S-type thermocouple are the thermoelectric potential, the thermoelectric potential rate is small, the sensitive reading is low, the mechanical strength decreases at high temperatures, it is very sensitive to pollution, and precious metal materials are expensive, so the one-time investment is large. This post was last edited by 263525689 at 2009-3-1 10:58 ]

Types of Thermometers A brief introduction to the following types of thermometers: 1. LCD thermometer: Liquid crystals made with different formulas have different phase transition temperatures. When their phase changes, their optical properties will also change, making the liquid crystal appear to change color. If liquid crystals with different phase transition temperatures are painted on a piece of paper, the temperature can be known from the change in color of the liquid crystal. The advantage of this thermometer is that it is easy to read, but the disadvantage is that it is not accurate enough. It is often used in ornamental fish tanks to indicate water temperature. 2. Resistance thermometer: The resistance of metal will increase with the increase of temperature. When the temperature changes little, its resistance is approximately linear with the temperature. In a larger temperature range, it can usually be expressed by a simple quadratic polynomial. By measuring the resistance of a metal, you can know what its temperature is. This kind of thermometer is usually made of platinum wire, can be accurate to 10-3 degrees, and is often used for precise measurements. Due to the high melting point of platinum, the measurable temperature range is wider, about -250 degrees Celsius to 1200 degrees Celsius. 3. Gas thermometer: At a fixed pressure, the volume of a gas with low density has a linear relationship with temperature. A thermometer made using this relationship is called a constant pressure gas thermometer. Under a fixed volume, the pressure of a gas with low density has a linear relationship with temperature. A thermometer made using this relationship is called a constant volume gas thermometer. 4. Rotary thermometer: Rotary thermometers are made of a crimped bimetallic sheet. One end of the bimetal piece is fixed, and the other end is connected to the pointer. Due to the different expansion degrees of the two metal sheets, the bimetallic sheet curls to different degrees at different temperatures, and the pointer points to different positions on the dial. The temperature can be known from the reading on the dial. 5. Semiconductor thermometer: The resistance change of semiconductors is different from that of metals. When the temperature increases, its resistance decreases and the change range is larger. Therefore, a small amount of temperature change can also cause significant changes in resistance. The resulting thermometer has high precision and is often called a thermometer. 6. Thermocouple Thermometer: A thermocouple thermometer consists of two strips of dissimilar metal connected to a sensitive voltmeter. Metal contacts will produce different potential differences at both ends of the metal at different temperatures. The potential difference is very small, so a sensitive voltmeter is required to measure it. You can know the temperature from the voltmeter reading. 7. Optical pyrometer: If the temperature of an object is high enough to emit a large amount of visible light, the amount of thermal radiation can be measured to determine its temperature. This type of thermometer is a light thermometer. This thermometer is mainly made of a telescope equipped with a red filter and a set of circuits with a small light bulb, a galvanometer and a variable resistor. Before use, first establish the relationship between the temperature corresponding to different brightness of the filament and the reading on the ammeter. When in use, align the telescope with the object to be measured and adjust the resistance so that the brightness of the bulb is the same as that of the object to be measured. At this time, the temperature of the object to be measured can be read from the galvanometer. 　

The common glass thermometers and thermocouples that I have seen in the laboratory are thermal expansion and contraction, and portable infrared thermometers that use resistance differences to measure temperature.

glass thermometer: Liquid expands in volume when heated ； -20~100℃, cheap, high precision, good stability, easy to damage, can only be installed in places where it is easy to observe. Bimetal thermometer: Metal expands linearly when heated ； -20~80℃, clear indication, good mechanical strength, low accuracy pressure thermometer: The gas or liquid in the temperature bulb changes pressure due to heating ； -50~600℃, cheap and easiest to detect on site. The mechanical strength of the capillary is poor and it is difficult to repair the thermal resistance thermometer after damage.: The resistance of a conductor or semiconductor changes with temperature ； -200~600℃, accurate measurement, can be used for low temperature or low temperature difference measurement. Compared with thermocouples, the maintenance workload is large and it is easy to be damaged in vibration situations.

Thermometer is the general term for temperature measuring instruments. Depending on the temperature measurement material used and the temperature measurement range, there are kerosene thermometers, alcohol thermometers, mercury thermometers, gas thermometers, resistance thermometers, thermocouple thermometers, radiation thermometers, optical thermometers, bimetal thermometers, etc.

There is no high temperature in our factory. So the commonly used ones are: Platinum resistance PT100 and PT1000, bimetal thermometer, pressure thermometer, glass thermometer, infrared thermometer (for inspection).

thermocouple thermometer: The junction of two different metal conductors generates thermoelectric potential when heated ； -50~1600℃ Accurate measurement, easier to install and maintain than thermal resistors, not easily damaged, requires compensation wires, higher installation costs Optical pyrometer: The brightness of the heating body changes with the temperature, 700 to 3200°C. It has a wide temperature measurement range, is easy to carry and use, and is cheap. It can only be measured visually, and you must be skilled to measure more accurate data. Photoelectric pyrometer: The color of the heating body changes with the temperature. 50~2000℃ has fast response speed, more accurate measurement, complex structure, high price, and troublesome reading. Radiation pyrometer: The radiant energy of the heating body changes with the temperature, 50~2000℃, the response speed is fast, and the error is large. Glass thermometer: Liquid expands in volume when heated ； -100~600℃, cheap, high precision, good stability, easy to damage, can only be installed in places where it is easy to observe. Bimetal thermometer: Metal expands linearly when heated ； -50~600℃, clear indication, good mechanical strength, low accuracy pressure thermometer: The gas or liquid in the temperature bulb changes pressure due to heating ； -50~600℃, cheap and easiest to detect on site. The mechanical strength of the capillary is poor and it is difficult to repair the thermal resistance thermometer after damage.: The resistance of a conductor or semiconductor changes with temperature ； -200~600℃, accurate measurement, can be used for low temperature or low temperature difference measurement. Compared with thermocouples, the maintenance workload is large and it is easy to be damaged in vibration situations.

My company has: Platinum resistance PT100: Resistance and temperature are linear over a certain range. Thermocouple: The potential difference between different metals at different temperatures is linear within a certain range. K, B, S bimetal thermometers are used: Different metals have different expansion coefficients. glass thermometer: Thermal expansion and contraction of liquids handheld infrared thermometer

bimetal thermometer: Metal expands linearly when heated ； Resistance thermometer with clear indication and good mechanical strength: The resistance of a conductor or semiconductor changes with temperature ； Accurate measurement, can be used for low temperature or low temperature difference measurement

Thermometer is the general term for temperature measuring instruments. Depending on the temperature measurement material used and the temperature measurement range, there are: kerosene thermometer, alcohol thermometer, mercury thermometer, gas thermometer, resistance thermometer, thermocouple thermometer, radiation thermometer, optical thermometer, bimetal thermometer, etc.