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Structure and principle of temperature sensor

TIME: 2017-11-30

(A) thermocouple thermometer

1, thermocouple thermometer principle and structure

Thermocouple thermometer is the use of two different contacts of the metal conductor, the thermoelectric power generated by the principle of the thermometer made measuring temperature. Mainly by the thermocouple, compensation wire and electrical measuring instruments (galvanometer) consists of three parts. Use one end of two different conductors or semiconductors (hot electrodes) to be welded to each other to form the working end (hot end) of the thermocouple, which is inserted into the measured medium to measure the temperature. Thermocouple's free end (cold end), respectively, through the wire and measuring instruments connected. When the working end of the thermocouple has a temperature difference with the free end, a thermoelectric potential is generated, and thus a current flows through the compensation wire, and the greater the temperature difference, the greater the thermoelectric power generated and the current on the conducting wire. By observing the deflection angle of the pointer on the measuring instrument, the temperature of the measured medium can be directly read out. Commonly used common platinum rhodium - rhodium thermocouple (WRLL type) * High measurement temperature of 1600 ℃. Ordinary Platinum Rhodium - Platinum Thermocouple (WRLB) * High measurement temperature of 1400 ℃. Ordinary nickel-chromium - nickel silicon thermocouple (WREU) * High measurement temperature of 1100 ℃.

Thermocouple thermometer has the advantage of high sensitivity, large measuring range, no external power supply, easy to remote measurement and recording. The disadvantage is the need to compensate for the wire, the installation costs more expensive. In industrial boilers, it is commonly used to measure steam temperature, furnace flame temperature and flue gas temperature in the flue.

2, the thermocouple thermometer installation and use requirements

(1) Thermocouple installation site should be easy to work, free from impact, vibration and other effects.

(2) The thermocouple shall be placed in the middle of the measured medium and shall be inclined at an angle of 45 ° to the flow direction of the measured medium as far as possible, with a depth not less than 150mm. Measuring furnace temperature, the general should be inserted vertically. If the vertical insertion difficulties, but also the level of installation, but the length inserted into the furnace should not be greater than 50Omm, otherwise it must be supported.

(3) After the thermocouple is installed, the plugging hole should be covered with muddy clay to prevent the measurement accuracy from being affected by external cold air intrusion. Ceramic thermocouple should be slowly inserted into the measured medium, so as to avoid sudden changes in temperature to rupture of the protective tube.

(4) The change of the free end temperature of the thermocouple has a great influence on the measurement result, and the temperature of the free end must be constantly calibrated or maintained.

(B) RTD thermometer

(1) RTD Thermometer is the use of conductor or semiconductor resistance changes with temperature made of the nature of the metal resistance by measuring the size, come to the measured temperature value. Common thermal resistance materials are platinum and copper.

(2) outside the thermal resistance generally need to add protective sleeve, protective sleeve material to temperature, corrosion resistance, withstand dramatic changes in temperature, good sealing and sufficient mechanical strength.

(3) Measuring the temperature below 500 ° C with the thermal resistance, higher accuracy than the thermocouple. Pin thermal resistance can measure -200 ~ 650 ℃, copper thermal resistance can measure the temperature range of -50 ~ 150 ℃. Thermal resistance can also be measured and displayed over long distances. Installation is similar to thermocouple. Thermal resistance and temperature display instrument through the wire connected to become temperature display device to measure the temperature of gases, liquids and steam.

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