Anhui Tiankang specializes in producing temperature meters, thermocouples, thermal resistors, bimetal thermometers and other temperature measuring instruments. Below the simple popularization of knowledge on temperature and temperature instruments:
Temperature is a physical quantity that characterizes the degree of coldness or heat of an object or system. According to the theory of molecular physics, the temperature reflects the violent degree of molecular irregular heat movement in an object. Many physical phenomena and chemical properties of objects are related to temperature, and many production processes, especially chemical reaction processes, are performed within a certain temperature range. Therefore, in industrial production and scientific experiments, people often encounter the problems of temperature and temperature detection and control.
First, the temperature scale is used to measure the height of the object of the scale, it is a numerical representation of the temperature, a temperature scale mainly includes two aspects: First, given a set of rules and methods of temperature quantification, such as the specified temperature The beginning of the reading (zero); the second is to give the unit of measurement of the temperature.
Common temperature scale introduction (1)Experienced temperature scale The temperature scale defined by the experimental method or empirical formula is called the empirical temperature scale by means of the relationship between the physical quantity of a certain substance and the temperature change. It mainly refers to the Celsius temperature scale and the Fahrenheit temperature scale. Both of these temperature scales are based on the volume expansion of the liquid (mercury) after it has been heated.
The Celsius temperature scale is a temperature scale that sets the freezing point of water to zero at standard atmospheric pressure and sets the boiling point of water at 100 degrees. Divide 100 equal parts between zero and 100 degrees, each equal to one degree Celsius, and the unit symbol is °C. Although the Celsius temperature scale is not an international uniform temperature scale, China can continue to use it for the time being.
The Fahrenheit temperature standard specifies that the freezing point of water at the standard atmospheric pressure is 32 degrees, the boiling point of water is 212 degrees, and the middle is divided into 180 equal parts, each equal to one degree Fahrenheit, and the unit symbol is. F. The Fahrenheit temperature scale has been eliminated by China and is no longer used.
It can be seen that the temperature values ​​determined with different temperature scales are different; in addition, the above-mentioned empirical temperature scale is a mercury thermometer as a temperature measurement medium, which is arbitrarily attached due to the nature of the specific substances and cannot strictly guarantee the countries of the world. The basic temperature measurement unit used is exactly the same.
(2) The thermodynamic temperature scale, also known as the Kelvin temperature scale, has the unit symbol K. The thermodynamic temperature scale is a theoretical temperature scale based on the second law of thermodynamics, which has been adopted by the International Metrology Congress as the basic temperature standard for international unification. It has an absolute zero and temperatures below zero cannot exist. The thermodynamic temperature scale is characterized by not being associated with a specific thermometer and is independent of the properties of the temperature measurement material. It is derived from Carnot's theorem. Therefore, the thermodynamic temperature expressed by the thermodynamic temperature scale is considered to be the ideal temperature measurement. value.
The Carnot heat engine in thermodynamics is an ideal machine that does not actually exist, so the thermodynamic temperature scale is an ideal theoretical temperature scale that cannot be directly implemented.
(3) International practical temperature scale In order to be practical and convenient, internationally decided to establish a temperature scale that can reflect thermodynamic temperature (that is, can guarantee high accuracy), and it is easy to use and easy to implement. This is the international practical temperature scale. Called the international temperature scale. The temperature scale selects some fixed point (reproducible equilibrium state) temperature as the reference point of the temperature scale; it specifies the reference instruments in different temperature ranges; the fixed point temperature adopts interpolation formulas; these formulas establish the standard instrument indication and international The relationship between temperature scale values. With the development of science and technology, the value of the fixed point temperature and the accuracy of the reference instrument will be higher and higher, and the precision of the interpolation formula will also be continuously improved. Therefore, the international temperature scale is continuously updated and improved, and the accuracy will be continuously improved. As close as possible to the thermodynamic temperature scale.
The first international temperature scale was established in 1927 and marked as ITS-27. Several major changes were made in 1948, 1968 and 1990, followed by ITS-48, ITS-68 and ITS-90. At present, China has begun to adopt ITS-90.
Second, the temperature detection instrument classification and characteristics Temperature detection based on the sensor and the measured medium contact is divided into contact and non-contact two categories.
Contact temperature measurement is characterized in that the temperature sensing element is in direct contact with the measured object, and the two are fully heat exchanged. Finally, the heat balance is achieved. At this time, the temperature of the temperature sensing element and the temperature of the measured medium are necessarily equal, and the value of the thermometer is indicated. It is the temperature of the measured medium. Contact temperature measurement accuracy is relatively high, intuitive and reliable, temperature measurement device is low, but because the temperature sensor and the measured medium are in direct contact, it will affect the thermal equilibrium state of the measured medium, and bad contact will increase the test. Temperature error; If the measured medium is corrosive or the temperature is too high, it will also seriously affect the performance and life of the temperature sensing element. According to the principle of temperature measurement conversion, contact temperature measurement can be divided into expansion type (such as temperature tube mercury thermometer, bimetal thermometer), thermal resistance type, thermoelectric type and other forms.
The non-contact temperature measurement is characterized in that the temperature sensing element does not directly contact with the measured object, but heat exchange is performed by receiving the thermal radiant energy of the measured object, and the temperature of the measured object is measured accordingly. Therefore, the non-contact temperature measurement has the advantages of not changing the temperature distribution of the measured object, having a small thermal inertia, and having a very high temperature measurement upper limit, which is convenient for measuring the temperature of the moving object and rapidly changing temperature. For example, infrared thermometers used by airports and schools to measure body temperature are non-contact thermometers.
The main features of the two types of temperature measurement methods:
(1) Contact:
Measurement conditions: The temperature sensing element should be in good contact with the measured object. The addition of the temperature sensing element hardly changes the temperature of the object. The measured temperature does not exceed the maximum temperature that the temperature sensing element can withstand: The measured object does not corrode the temperature sensing element.
Measuring range: It is especially suitable for continuous online temperature measurement of 1200 °C, with large heat capacity and non-corrosive objects. It is difficult to measure temperature above 1300 °C.
Accuracy: Industrial watches are usually 1. O, 0.5, 0.2, and 0.1 levels, the laboratory table up to 0. 01 level.
Response speed: slow, usually tens of seconds to several minutes
(2) Non-contact:
Measurement conditions: The surface emissivity of the object to be measured needs to be accurately known; the radiant energy of the object to be measured is sufficiently applied to the detection element.
Measuring range: In principle, the measurement range can be from ultra-low temperature to very high temperature, but below 1000°C, the measurement error is large, and the temperature of the moving object and the object with small heat capacity can be measured.
Accuracy: Usually 1.0, 1.5, 2.5.
Response speed: fast, usually 2-3s.
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