Monday, April 25, 2011

【 Weak current College 】 thermal resistance of principle】



Thermal resistance is the most commonly used in low temperature region of a temperature detector. Its main characteristic is the measurement of high precision, stable performance. With the Platinum thermal resistance measurement accuracy is the highest, it is not only widely used industrial Thermometry, and be made into a standard benchmark instrument.
1. thermal resistance measurement principle and materials
Thermal resistance measurement is based on the metal conductor resistance with temperature increases this characteristic for temperature measurement.
Thermal resistance are mostly composed of pure metal materials, used at present is the highest number of Platinum and copper, in addition, it has been used since Austin, nickel, manganese and rhodium materials manufacturing thermal resistance.
2. thermal resistance of structures
(1) master-RTD, resistance temperature measurement principle from the measured temperature changes directly through RTD resistance changes to measure, therefore, the thermal resistance of the PIN and other conductor resistance changes will impact for temperature measurement. To eliminate the effects of lead resistance with using three-wire or 4-wire.
(2) armored resistance armored resistance is determined by the heat element (resistance), leader, insulating materials, stainless steel casing with a combination of a solid body, as in Figure 2-1-7 shows, its diameter is 2 ~ φ φ 8 m m, minimum up to φ m m.
Compared with ordinary thermal resistance, it has the following advantages: ① small, no air gap inside the thermal inertia, small measuring latency; ② good mechanical properties, excellent resistance to vibration and shock resistant; ③ can bend, easy to install ④ long service life.
(3) end end RTD RTD temperature sensor components by special treatment resistance wire-wound, close to the end of the thermometer, it and General axial resistance compared to more accurately and quickly to reflect the actual measured surface temperature, suitable for measuring bearing and other parts of the surface temperature.
(4) flameproof thermal resistance flameproof thermal resistance through special structure of the terminal box, inside the shell due to the explosive gas mixture is sparks or arcs, impact and explosion confined in the terminal box, production site will not be cited-explosion. Flameproof thermal resistance can be used for Bla ~ B3c-area with explosion risk areas of temperature measurement.
3. the composition of the thermal resistance temperature measurement system
Thermal resistance measurement system by thermal resistance, wire and display instruments, etc. You must note the following points:
① RTD and display instrument of indexing codes must be consistent
② to eliminate wire resistance changes, you must use three-wire connection. Specific details see this chapter III.
(2) armored resistance armored resistance is determined by the heat element (resistance), leader, insulating materials, stainless steel casing with a combination of a solid body, its diameter is 2 ~ φ φ 8 m m, minimum up to φ m m.
Compared with ordinary thermal resistance, it has the following advantages: ① small, no air gap inside the thermal inertia, small measuring latency; ② good mechanical properties, excellent resistance to vibration and shock resistant; ③ can bend, easy to install ④ long service life.
(3) end end RTD RTD temperature sensor components by special treatment resistance wire-wound, close to the end of the thermometer, it and General axial resistance compared to more accurately and quickly to reflect the actual measured surface temperature, suitable for measuring bearing and other parts of the surface temperature.
(4) flameproof thermal resistance flameproof thermal resistance through special structure of the terminal box, inside the shell due to the explosive gas mixture is sparks or arcs, shadow
Resistance of circuit breaker repair must change resistance wire length and impact resistance values, the replacement of the resistance of the body as well, the use of welding repairs, welding to validate qualified to use.

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