The choice of the temperature measuring instrument

1) The choice of the in situ temperature instrument bimetallic thermometer: in meet the measuring range, working pressure and accuracy requirements, should be preferable. Pressure type thermometer: - Low temperature under 80 oc, couldn't close observation, a vibration and accuracy requirements is not high occasions can choose. Glass thermometer: because mercury pollution, is generally not recommended. Except as a complete set of machinery, measurement accuracy is not high under the condition of use. 2) The choice of thermocouple temperature measurement for general situation, thermal resistance suitable for no vibration, thermal resistor is fit for measuring the response speed of the occasion demands. According to the requirement for measuring response speed, can choose: thermocouple 600 s and 100 s, 20 s level 3; Thermal resistance of 90 ~ 180 s, 30 ~ 90 s, 10 ~ 30 s, & lt; L0s level 4; Thermistor & lt; 1 s。 3) Choose according to use environment condition thermometer junction box: ordinary type condition good place; Splash proof, water proof, damp or outdoor places; Tu isolation type: places where inflammable, explosive; Socket type: only applicable to special occasions. 4) Connection mode choice usually can choose threaded connection, the following situations should choose flange connection ways: (1) to install on lining equipment, pipeline and non-ferrous metal pipe; (2) crystallization, scarring, jams, and the corrosive medium; (3) medium inflammable, explosive and poisonous. 5) Special occasions, the choice of the thermometer (1) temperature & gt; 870 ℃, hydrogen content & gt; 5% of the reducing gas, inert gas and vacuum occasions, choose tungsten-rhenium thermocouples or blowing thermocouple; (2) of equipment, the outer wall of pipeline and surface temperature, choose the surface or armoured thermocouple, heat resistance; (3) containing hard solid granules medium, choose wear-resisting thermocouple; (4) in the same detecting element to protect casing, require multi-point temperature measurement, choose a thermocouple. （ 2) The installation of the temperature measuring instrument 1) Measuring accuracy of consider (1) side temperature components installed on the pipeline, should guarantee the temperature measuring elements and fluid full contact, therefore, demand falling in to test components to meet flow measured medium, at least with the measured medium flow into 90 o, never measured medium and form downstream; (2) install mercury thermometer or thermocouple, if the nominal pipe diameter is less than 50 mm, and installing resistance thermometer or bimetallic thermometer nominal pipe diameter less than 80 mm, the thermometer should be installed in the expansion of arm; (3) the work side of temperature measuring element in pipe flow rate, biggest expansion thermometer should be the center of the temperature measuring points in pipe line, thermocouple, platinum thermal resistance, copper thermal resistance to protect casing should be across the beam center line at the end of 5 ~ 10 mm, 50 and 25 ~ 30 mm to 70 mm. The center of the pressure gauge thermometer bulb deficiency with the center line of the pipeline; (4) to have enough insertion depth, falling in to to reduce the measurement error; (5) thermocouple and thermal resistance of the junction box should be down, to escape the rain water or other liquid infiltration affect measurement, thermocouple shall not have a strong magnetic field; 6 to reduce temperature lag, but outside the protection and protection of casing pipe with good heat transfer between fillers, such as transformer oil ( < 150℃) Or copper chip, quartz sand, > 150℃) 。 2) The selection of measuring temperature protection tube (1) detecting element insertion length choice: the insertion length should be selected to detect components sensitive to temperature changes measured medium, and the position of representative for the principle. (2) temperature protection pipe material qualitative choice: should be selected according to the conditions of the measured medium right. 3) On pipeline equipment installation generally has two kinds: (1) threaded head fixed; Threaded head fixed way, no corrosive medium is generally applicable to pipe installed on the temperature measuring element. Has the advantages of small size, installation is relatively compact. (2) the flange fixed. Flange fixed way, suitable for temperature measuring element installed on the equipment. In high temperature and strong corrosive medium, the coking in slurry medium, virulent, powder medium and catalyst layer of multi-point temperature measurement, also should use the flange fixed way, with convenient maintenance. Note: the article reprinted in WeChat public account