Insertion depth instructions for bimetallic thermometers and thermal resistors

Bimetallic thermometers are divided into three types: ordinary type, outdoor type, and anti-corrosion type. The ordinary type has an electroplated iron shell and a stainless steel protective tube, which is suitable for general indoor use. The outdoor type has an aluminum shell, and the protective tube and connecting column are made of stainless steel. It has good sealing performance and is suitable for indoor and outdoor use and general corrosion-resistant places. The anti-corrosion type has a full stainless steel shell, and the protective tube and connecting column can be made of molybdenum-titanium material. The connecting parts are all sealed with sealant, which can be used for the measurement of most corrosive media and gases. When the temperature changes, the two different materials of the bimetallic strip have relatively large differences in linear expansion coefficients, resulting in different expansion and contraction, causing the bimetallic strip to bend and deform. The thermal resistor with a protective sleeve has heat transfer and heat dissipation losses. In order to reduce measurement errors, the bimetallic thermometer and thermal resistor should have sufficient insertion depth:
1. For thermal resistors that measure the temperature of the fluid in the center of the pipeline, the measuring end should generally be inserted into the center of the pipeline (vertically or tilted). If the pipe diameter of the measured fluid is 200 mm, the insertion depth of the thermal resistor should be 100 mm;

2. 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;

3. 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;

4. 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.