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1. Manufacturing principle and structure of thermometers 1.1 Manufacturing principle In terms of manufacturing principles, thermometers are divided into three categories:: 1.1.1 Liquid-filled type—When the temperature changes, the liquid will expand or contract accordingly. 1.1.2 Gas-filled type—When the temperature changes, the gas will expand or contract accordingly. 1.1.3 Bimetallic type - The sensing element of the bimetallic thermometer is composed of two metals with different thermal expansion coefficients and is in a spiral shape. They will deform according to changes in temperature to indicate the temperature. feature: This thermometer has virtually no ambient temperature error compared to liquid-filled thermometers ； Since it is not filled with liquid, its use is very safe (no environmental pollution) ； This thermometer has a simple structure and a reasonable price. 1.2 Thermometer structure 1.3 Thermometer terminology 1.3.1 Table diameter Φ60Φ75Φ100Φ150 1.3.2 Snake tube, connection diameter, capillary tube, temperature sensing part 2. Thermometer classification 2.1 Bourdon tube thermometer type ordinary thermometer: TL□□, RL□□, RV□□, TV□□ Thermometer with contact: TE□□, TF□□, TK□□, TD10, TD21, TD25 (pressure-resistant and explosion-proof) temperature switch: TS40, TS50, TD50 (pressure-resistant and explosion-proof) TS40 IP level is low, indoor TS50 IP level is high, outdoor TD50 pressure-resistant and explosion-proof switch temperature transmitter: TH□□ TH61 TH71 TH81 Model type Temperature range Application industry TB□□ Bimetal thermometer-50℃～500℃ Food, cosmetics, pharmaceutical TL□□ Thermometer-200℃～600℃ General industrial use RL□□ Rainproof thermometer-200℃～600℃ Outdoor, corrosion-resistant, high protection level RV□□ Vibration-resistant thermometer -200℃～600℃ Used in strong vibration situations TE□□ With micro switch 0℃～600℃ For general industrial use (internal liquid filling) TK□□ With contact switch -70℃～600℃ Inflammable and explosive situations TF□□ With micro switch -70℃～300℃ For general industrial use TD10.21.25 Explosion-proof thermometer - 70℃ ~ 600℃ flammable and explosive occasions TS Temperature switch - 30℃ ~ 600℃ general industrial use TD50 Explosion-proof thermometer - 30℃ ~ 600℃ flammable and explosive occasions 3. Thermometer selection and quotation 3.1 First determine the type of thermometer according to customer needs, and then determine the model according to the place of use ； type: Ordinary thermometer, thermometer with contact, temperature switch, temperature transmitter ； There are the following three situations of use:: For outdoor use, corresponding models require high protection level and corrosion resistance.: RB□□, RL□□ In situations with strong vibration (stainless steel, liquid-filled type) Corresponding models: RB□□, RL□□ Corresponding models for flammable and explosive situations: TD□□ 3.2 Selection of thermometer shape and installation method 3.2.1 Shape and installation method: Advantages and Disadvantages Direct type Since the indicator and temperature sensing part are both direct, installation can be carried out by simply using connecting bolts. Since the indicator and temperature sensing part are directly connected, the thermometer is easily affected by the liquid being measured. The L-shaped vertically installed indicator can rotate freely, so reading is convenient and simple. Although the L-shaped vertically mounted indicator can rotate freely, the fixing bolts may become loose due to the use of gaskets when installing the thermometer. Advantages Disadvantages The remote transmission type can read the temperature at different locations other than the measurement point. Errors will occur in mercury-filled thermometers when the height of the indicator and the temperature sensing part are different. 3.2.2 Thermometer dial scale and temperature sensing part material selection ※When selecting a thermometer, consider that the range of the temperature to be measured should be between 30% and 60% of the temperature dial scale under normal circumstances. When the temperature exceeds this range, the meter may rupture. For example: Special attention should be paid to the thermometer during transportation, passing through the equator or cold zone, or being stored in the cold zone! application: If the actual measured liquid temperature is 40℃~60℃, then the dial scale should be selected from 0~100℃. ※Confirm whether the material of wetted parts is suitable for the liquid or gas to be measured. 3.2.3 The minimum insertion size of the temperature sensing part varies according to the model. The temperature range and the diameter of the temperature sensing part jointly determine its minimum insertion depth. It cannot be less than 1/3 (insertion/length). When ordering, after selecting the specifications, you need to choose an appropriate length, which must be greater than the shortest insertion depth to ensure performance. 3.2.4 Ambient temperature compensation method When the ambient temperature around the thermometer changes, the liquid in the indicator and capillary tube will expand or contract accordingly, and then the indication error will occur. The following two compensation methods can compensate for this error. a. Bimetal compensation: ①Measuring the actual temperature ② Measuring the ambient temperature is suitable for the situation where the ambient temperature changes around the indicator and the wire are consistent b. Conduit compensation is suitable for the situation where the ambient temperature around the indicator and the wire changes independently. The temperature around the indicator changes very little, while the temperature around the wire changes greatly, and vice versa. Each part of the wire is under different ambient temperatures. A part of the wire is heated 3.2.5 Protective tube If the following conditions occur, a protective tube should be used to protect the temperature sensing part. For anti-corrosive fluids, it is necessary to use a protective tube made of appropriate materials. If high pressure occurs, it is necessary to use a protective tube adapted to the working pressure. If the fluid is flowing, it is necessary to use a protective tube with appropriate flow rate and flow rate. If fluid leaks when the thermometer is unplugged, it is necessary to use a protective tube. If the filling liquid in the thermometer leaks from the sensor, it is necessary to use a protective tube.