temperature detection instruments and
a temperature measurement of the basic concepts of
temperature is hot and cold characterization of the degree of physical objects. Temperature only through objects with temperature changes in the characteristics of some of the indirect measurement, and the objects used to measure the temperature scale called the numerical temperature scale. It provides temperature readings starting point (zero) and the basic unit of measurement of temperature. At present, more use of the temperature scale Fahrenheit temperature scale there, Celsius temperature scale, thermodynamic temperature scale and international practical temperature scale.
Fahrenheit temperature scale (oF): In the standard atmospheric pressure, the ice melting point of 32 degrees, the boiling point of water for the 212, 180 sub-divided in the middle of each section is divided into a newspaper's degrees, for the symbol oF.
Celsius ( ): In the standard atmospheric pressure, the ice melting point is 0 degrees, the boiling point of water is 100 degrees, 100 sub-divided in the middle of each section is divided into a newspaper's degrees, for the symbol .
thermodynamic temperature scale, also known as Kelvin temperature scale, or absolute temperature scale, it provides elements of the campaign to stop when the temperature of absolute zero, remember to sign K.
international practical temperature scale is an international agreement of temperature scale, with its thermodynamic temperature scale similarity to the current complex and high precision, easy to use. At present, the international temperature scale is the 1975 15th International General Assembly adopted the right time "in 1968 international practical temperature scale -1975 Revision," to remember: IPTS-68 (Rev-75). However, Wen said IPTS-68 There is a certain lack of metering of the International Committee of 18 in the seventh session of the General Assembly of the International Measurement resolution to authorize the 1989 session in 1990 adopted the International Temperature Scale ITS-90, ITS-90 temperature scale alternative IPTS-68. Since January 1, 1994 from the full implementation of ITS-90 international temperature scale.
1990 of the International Temperature Scale (ITS-90) Following is a brief introduction.
1. Temperature unit
thermodynamic temperature (as a symbol T) is a basic physics hands, and its units Kelvin (as a symbol K), defined as the point of the three-phase water temperature thermodynamics 1/273.16. As the previous definition of the temperature scale, with the use of 273.15K (freezing point) to indicate the temperature difference, so it is still the method.
by definition, equal to the size of degrees Kelvin, the temperature difference can also be used degrees Kelvin, or expressed.
international temperature scale ITS-90 at the same time the international definition of Kelvin temperature (symbol for the T90) and the International Celsius (symbol for t90)
2. International Temperature Scale of ITS-90 General
ITS-90 from 0.65K up to the Planck radiation law of the use of monochromatic radiation actual measurable The maximum temperature. ITS-90 is formulated this way, that is, in the whole range, the T90 temperature of any value is very close to T when the temperature scale adoption of best estimate, and compared to the direct measurement of thermodynamic temperature, T90 measurement to be much more convenient and more For the precision and high reproducibility.
3. ITS-90 definition of
temperature for the first 0.65K to 5.00K between, T90 by the 3He and the 4He vapor pressure and temperature to define the relationship.
second temperature 3.0K for the three-phase to the point of neon (24.5661K) between the T90 with helium Gas thermometer to define.
temperature for the second three-phase hydrogen balance point (13.8033K) to the freezing point of silver (961.78 ) between, T90 by the PRT to the definition. It uses a set of provisions of the definition and use of a fixed point within the provisions of Interpolation to indexing.
silver freezing point (961.78 ) over the temperature, T90 is based on Planck's radiation law to define, are complex instruments for the optical pyrometer.
Second, the temperature measuring instruments classified
temperature measurement instrument by way of temperature measurement can be divided into contact and contactless two broad categories. In general, contact Thermometer Thermometer is relatively simple, reliable, high precision measurement; but with the temperature measured media components needed to pay the full heat of kumgang, helping take some time to reach thermal balance, so there is measuring Wen's delay, at the same time by high-temperature materials limitations, can not be used for high temperature measurement. Non-contact temperature measurement instrument through the principle of heat radiation to measure temperature, the temperature components under test and no media access, wide temperature range, from the maximum temperature of the restrictions would not undermine the detected objects temperature field , The general reaction speed is also faster; but by the object emissivity, measuring the distance, smoke and dust and water vapor, and other external factors, the more error measurement.
three thermocouple
thermocouple is the industry's most commonly used one of the temperature detection devices. The advantage is:
high-precision measurements. Thermocouple as a result of direct contact with the measured object, from among the media.
wide range. Commonly used thermocouple from -50 ~ 1600 can be continued while surveying, some of the special thermocouple to the lowest measurable -269 (such as nickel-chromium Jin), up to 2800 (such as tungsten - Re).
simple and easy to use. Thermocouples are often made from two different kinds of wire, but not at the beginning of the size and limitations, outside the protection of casing, it is very easy to use.
1. The basic principles of thermocouple temperature
two different conductor or semiconductor materials A and B welded together to form a closed loop , 2-1-1 figure by
show. When the conductor of the A and B two points persistent 1 and 2 between the temperature difference, between the two will have a force, which in
to form a loop in the size of the current, a phenomenon known as the thermal effect. Thermocouple is the use of this effect to work
made.
2. Thermocouple type of structure and the formation of
(1) the type of thermocouple
common thermocouples and thermocouple standards can be divided into two major categories of non-standard thermocouple. The call is the national standard thermocouple
standards for its thermal power and temperature, allowing error, and the reunification of the sub-standard forms degree of thermocouple, which
have showed their support of the instruments available for selection. Thermocouple in the use of non-standardized order of magnitude or scope of the standard and not
of thermocouple, in general there is no uniform grading scale for the measurement of certain special occasions.
standardization of China's thermocouple from January 1, 1988, the thermocouple and heat resistance by all international standards IEC production, and designated S, B, E, K, R, J, T standardization of seven thermocouple China-based design for the reunification of the thermocouple.
(2) thermocouple in the form of the structure of the thermocouple in order to ensure a reliable, steady work, it follows the structure of the request:
thermocouple two fever component of welding electrodes must be strong;
hot electrode between the two should be well insulated to prevent a short circuit;
compensation thermocouple wire with the free end of the connection to reliable and user-friendly;
should be able to guarantee the protection of casing hot electrode and harmful media full isolation.
3. Thermocouple cold junction temperature compensation
as a result of the thermocouple materials in general are more expensive (especially when the use of precious metals), and the temperature to a point very far away from the instrument, the thermocouple in order to save materials, reduce costs, compensation is usually used to wire thermocouple The cold side (free end) into the relatively stable temperature control room, connected to the terminal on the instrument. It must be pointed out, the thermocouple wire compensation only an extension of the role of the hot electrode, so that the thermocouple cold end to the control room of the mobile terminal on the instrument itself can not eliminate the cold-side temperature of temperature, can not afford to compensate Role. Therefore, the need to adopt amendments to other methods to compensate for the cold-side temperature t0 0 when the temperature measurement.
in compensation for the use of thermocouple wire should be noted that when the match type, can not pick the wrong polarity, the Compensation and thermocouple wire to connect the terminal temperature should not exceed 100 .
four, heat resistance
in low-temperature heat resistance is the most commonly used in a temperature detector. Its main feature of high-precision measurement performance and stability. Platinum is one of thermal resistance measurement accuracy is the highest not only widely used in industrial temperature measurement, and was made of standard benchmark instrument.
1. RTD temperature measurement principles and materials
thermal resistance measurement is based on the metal conductor The value of the resistance with temperature increases to the characteristics of temperature measurement.
thermal resistance from most of the pure metal material, is currently the most widely used platinum and copper, in addition, has now begun to adopt Austin, nickel, manganese and rhodium, and other materials heat resistance.
2. Thermal resistance of the structure of
(1) good heat-resistance of commonly used industrial heat resistance temperature components (resistors) of the structure and characteristics of the table 2-1-11. RTD temperature measurement from the principle, we can see that the temperature change is measured directly through the thermal resistance of the resistance to changes in the measurement, heat-resistance of Lead wire resistance and other changes will impact on temperature measurement. Lead to the elimination of the impact of resistance as with the use of three-or four-wire system, the specific contents of the section I see in this third chapter.
(2) sheathed heat resistance sheathed by the heat resistance temperature components (resistors), lead, insulation materials, stainless steel casing of the combination of a solid body, as shown in Figure 2-1-7, and its For the general diameter 2 ~ 8mm, up to the smallest mm.
ordinary heat-resistance, it has the following advantages: small, no internal air gap, thermal inertia, the measurement of small lag; good mechanical properties, vibration resistance, impact resistance; be able to bend, easy to install using Long life.
(3) end-end thermal resistance heat resistance temperature components of the special treatment by the resistance wire around the system, keep the thermometer in the end, the structure shown in Figure 2-1-8. It is generally axial thermal resistance compared to more accurately reflect the rapid test and the actual end-temperature measurements apply to the bearing and other mechanical end of the temperature.
(4) heat-proof barrier-blasting through the special structure of the thermal resistance of the junction box, its internal shell as a result of an explosive mixture of gas by sparks or arc, and other effects of the explosion limited to the cable box, not on-site production Super explosion will be cited. Explosion-proof thermal resistance can be used to Bla ~ B3c-class area with a risk of an explosion of temperature measurement sites.
3. RTD temperature measurement system
RTD temperature measurement system in general by the thermal resistance, and connecting wires show Instrument, and other components. Must pay attention to the following two points:
heat resistance and shows that the instrument must be at the same time,
In order to eliminate the wires connecting the impact of changes in the resistance, to adopt the three-wire connection. See the specific content of this Chapter.
(2) sheathed heat resistance sheathed by the heat resistance temperature components (resistors), lead, insulation materials, stainless steel casing of the combination of a solid body, as shown in Figure 2-1-7, and its For the general diameter 2 ~ 8mm, up to the smallest mm.
ordinary heat-resistance, it has the following advantages: small, no internal air gap, thermal inertia, the measurement of small lag; good mechanical properties, vibration resistance, impact resistance; be able to bend, easy to install using Long life.
(3) end-end thermal resistance heat resistance temperature components of the special treatment by the resistance wire around the system, keep the thermometer in the end, the structure shown in Figure 2-1-8. It is generally axial thermal resistance compared to more accurately reflect the rapid test and the actual end-temperature measurements apply to the bearing and other mechanical end of the temperature.
(4) heat-proof barrier-blasting through the special structure of the thermal resistance of the junction box, its internal shell explosive mixture due to arcing or sparks, such as video
resistance of the open-repair resistance to change is bound to affect the length of wire resistance, the replacement of this new body for the resistance, the use of a welding repair, welding and after going to check before they can use the pass.
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The basic concept of measuring temperature
A new type of digital, networked sensors in engineering