How to install bimetallic thermometer to improve temperature measurement accuracy

The working principle of the bimetallic thermometer is to use two metals with different temperature expansion coefficients, one end is welded at a fixed point, and the other end is twisted and deformed when the temperature changes, which is converted into a pointer deflection angle to indicate the temperature. When installing the bimetallic thermometer, attention should be paid to accurate temperature measurement, safety, reliability and convenient maintenance, and it should not affect the operation of the equipment and production operations. To meet the above requirements, the following points should be noted when selecting the installation location and insertion depth of the thermal resistor:

(1) In order to ensure sufficient heat exchange between the measuring end of the thermal resistor and the measured medium, the measuring point position should be reasonably selected, and the thermal resistor should be installed near the dead corners of valves, elbows, pipelines and equipment as much as possible.

(2) The thermal resistor with a protective sleeve has heat transfer and heat dissipation losses. In order to reduce measurement errors, the thermocouple and thermal resistor should have sufficient insertion depth:

a. For the thermal resistor measuring the temperature of the fluid in the center of the pipeline, its measuring end should generally be inserted into the center of the pipeline (vertical installation or inclined installation). If the pipe diameter of the measured fluid is 200 mm, the insertion depth of the thermal resistor should be 100 mm;

b. For the temperature measurement of high-temperature, high-pressure and high-speed fluids (such as main steam temperature), in order to reduce the resistance of the protective sleeve to the fluid and prevent the protective sleeve from breaking under the action of the fluid, the protective tube can be shallowly inserted or a heat sleeve thermal resistor can be used. The shallow insertion thermal resistor protective sleeve should be inserted into the main steam pipe to a depth of not less than 75 mm; the standard insertion depth of the heat sleeve thermal resistor is 100 mm;

c. If the temperature of the flue gas in the flue needs to be measured, even if the flue diameter is 4 m, the insertion depth of the thermal resistor is 1 m;

d. When the insertion depth of the measuring element exceeds 1 m, it should be installed vertically as much as possible, or a support frame and protective sleeve should be installed.