Bimetal thermometer is an on-site detection instrument for measuring low and medium temperature. It can directly measure the temperature of liquid vapor and gaseous medium in the range of -80℃-+500℃ in various production processes.

main feature
Display temperature on site, intuitive and convenient
Reliable and long service life;
The core-pulling thermometer can maintain or replace the movement in a short time without stopping the machine.
Axial type, radial type, 135o type, universal type and other varieties are complete, suitable for various on-site installation needs.

working principle

The bimetal thermometer is based on a bimetallic sheet wound into a circular bending shape. When one end is heated and expanded, it drives the pointer to rotate, and the working instrument displays the temperature value corresponding to the thermoelectric potential.

Bimetal thermometer is an on-site detection instrument for measuring low and medium temperature. It can directly measure the temperature of liquid vapor and gaseous medium in the range of -80℃-+500℃ in various production processes. The main component of an industrial bimetal thermometer is a multi-layer metal sheet composed of two or more metal sheets laminated together. It works on the principle that two different metals expand at different degrees when the temperature changes. When the temperature changes, the free end of the temperature sensing device rotates accordingly, driving the pointer on the thin shaft to produce an angle change, and the corresponding temperature is indicated on the dial.

Structure analysis of bimetal thermometer

The working principle of the bimetal thermometer is to use two kinds of metals with different temperature expansion coefficients. In order to improve the temperature measurement sensitivity, the metal sheet is usually made into a spiral shape. When the temperature of the multilayer metal sheet changes, the amount of metal expansion or contraction of each layer Not waiting to make the spiral roll up or loose. Bimetallic thermometer uses bimetallic spiral material as temperature sensing element. The fixed end of the bimetallic spiral temperature sensing element is welded to the protection tube, and the other end is the free end connected to the watch shaft equipped with pointers. When the temperature of the measured medium changes, the bimetallic spiral temperature sensing element is twisted, and its free end Drive the needle to rotate, and directly read the temperature value of the measured medium on the dial.
Because one end of the spiral coil is fixed and the other end is connected with a pointer that can rotate freely, when the bimetallic piece feels a temperature change, the pointer can indicate the temperature on a circular graduation scale. The temperature measurement range of this instrument is -20℃-+500℃, and the allowable error is about 1.5% of the scale range.


Radial Bimetal Thermometer_What are the advantages of thermocouple and bimetal thermometer

The thermocouple and the bimetal thermometer are very close, but they are different when measuring the temperature difference. The bimetal thermometer is more suitable to be used in the field of detecting the low temperature state, and it can be measured during the measurement. For the temperature of gaseous medium and liquid vapor at minus 80 degrees Celsius to 500 degrees Celsius, thermocouples are mostly used in industrial high temperatures, while bimetal thermometers are more reasonable in low temperature environments. Bimetal thermometers** *The main element is a multi-layered metal sheet made of one or more metal sheets. The difference in expansion degree at different temperatures is used as the working principle. When one end is heated and expands, the pointer will be changed. Drive it to rotate, and the corresponding temperature value will be displayed on the working instrument.
Thermocouple is the most commonly used temperature detector in the medium and low temperature zone. Its main feature is high measurement accuracy and stable performance. Among them, the measurement accuracy of platinum thermal resistance is the highest. It is not only widely used in industrial temperature measurement, but also made into a standard reference instrument. The temperature sensing element of the metal thermal resistance has a quartz sleeve cross frame structure, and the twist frame structure has a rod structure. Thermal resistance is a primary element that converts temperature conversion to resistance value conversion. Usually, the resistance signal needs to be transmitted to a computer control device or other primary instrument through a lead. Industrial thermal resistors are installed at the production site and there is a certain distance between them and the control room, so the lead wires of thermal resistors will have a greater impact on the measurement results.
Prevention of leakage of thermocouple
1. Keep the thermocouple not in contact with the refractory bricks.
2. Ground the negative pole of the thermocouple to eliminate the leakage signal on the thermocouple.
3. Install a filter device at the output end of the thermocouple.
4. Lead the ground wire from the hot junction of the thermocouple to ground.
5. Add a heat-resistant steel pipe or silicon carbide tube to the thermocouple tube and ground it.

The principle and use method of radial bimetal thermometer

1. Subject content and scope of application This standard specifies the terms and definitions, product classification, technical requirements, test methods, inspection rules, signs, packaging, etc. of industrial bimetal thermometers (hereinafter referred to as thermometers). This standard is applicable to the temperature detection element consisting of a bimetal element and a sheath, with a circular dial, and a thermometer with a measuring range of -80～+500℃.

2. Reference standards

ZBY 002 Basic environmental conditions and test methods for transportation, transportation and storage of instruments and meters ZBY003 Technical requirements for packaging of instruments and meters ZBY120 Working conditions of industrial automation instruments-temperature, humidity and atmospheric pressure ZBY122 Basic type, size and generality of pointer indication parts of industrial automation instruments Technical requirements ZBY123 General provisions for scale of industrial automation instrument ZBY247 Terminology of industrial automation instrument

3. Terms and definitions In addition to ZB Y247, the following terms and definitions apply to this standard.

　　3.1 Angle type The type in which the axis of the detection element is perpendicular to the plane of the dial, also known as the axial type. 3.2 Straight type The type in which the axis of the detection element is parallel to the plane of the dial is also called radial type. 3.3 Insertion length The length from the lower end of the detection element to the lower end of the joint surface of the installation connection or the lower end of the taper thread (see L in Figure A1 ~ A4 in Appendix A). 3.4 Insertion length The length of the detection element in the measured medium from the bottom of the detection element.

4. Product classification and basic parameters

4.1 Type thermometers are divided into the following four types according to the connection and installation methods of the indicating device and the detection element: a radial b axial c universal d. angular type approved by the Ministry of Machinery and Electronics Industry 1988-06-12 -1989-01-01 implementation

　　4.2 Nominal diameter of dial The nominal diameter of dial of thermometer is 60, 100, 1500mm

　　4.3 Measuring range The measuring range of the thermometer should meet the requirements of Table 1. Table 1 Measurement range -80 ～ +40 -40 ～ +80 0 ～50 0 ～100 0 ～150 0 ～200 0 ～300 0 ～400 0 ～500

　　4.4 Accuracy grade The accuracy grade of the thermometer is 1, 1.5, (2.5) Note: The accuracy grades in parentheses are not recommended.

　　4.5 Detection element diameter and installation thread The detection element diameter and installation thread should meet the requirements of Table 2. Nominal diameter of dial Detecting element diameter Mounting thread 60 4, 6 M 16×1.5 100, 150 8, 10 M27×2

　　4.6 Insertion length The insertion length of the thermometer is 75, 100, 150, 200, 250, 300, 400, 500mm. Note: If the insertion length is greater than 500mm, it shall be agreed between the manufacturer and the user.

　　4.7 Nominal pressure of sheath The nominal pressure of the thermometer sheath should be selected from 1.0, 1.6, 2.5, 4.0, 6.4MPa series.

　　4.8 Installation and connection methods The installation and connection methods of the thermometer are divided into the following four (see Appendix A); a. Adjustable pipe joints; b. Pipe joints (external thread); c. Pipe joints (internal thread); d. Fixed threads.

　　4.9 Indicating adjustment mechanism Thermometers are classified into the following three types according to whether the indicating device has an indicating adjustment mechanism: a. No indicating adjustment mechanism; b. External indicating adjustment mechanism; c. Internal indicating adjustment mechanism.

5. Technical requirements

　　5.1 Normal working conditions The normal working conditions of the thermometer should meet the requirements of Table 3. Table 3 Workplace Temperature ℃ Relative Humidity% Covered Place -25 ～ +55 5 ～ 100 Outdoor Place -40 ～ +85 5 ～ 100 Note: Special working conditions are negotiated by the manufacturer and the user.

5.2 Appearance, structure and assembly quality The appearance, structure and assembly quality of the thermometer shall meet the following requirements: a. The parts of the thermometer shall not be rusted, and the protective layer shall be firm, uniform and smooth; b. The glass or other transparent materials on the surface of the thermometer shall Keep it transparent, and there must be no defects that hinder correct readings; c. The type, basic parameters and dimensions of the thermometer (size tolerance according to the relevant regulations of the manufacturer) should comply with the provisions of Chapter 4; d. The pointer and dial of the thermometer should comply with ZBY122 and The provisions of ZBY123; the length of the pointer (the length of the pointer's rotation center to the indicated******) should meet the requirements of Table 4; the distance between the pointer indicating part and the dial plane should not be greater than 5mm; the circular scale is 270 ° ~ 300 ° part of the circle; pointer, dial, scale and signs should not change or fade. Table 4 Nominal diameter of scale plate Pointer length 60 ≥23 100 ≥36 150 ≥57

　　5.3 Basic error limit The basic error limit of the thermometer should meet the requirements of Table 5. Table 5 Accuracy grade Basic error% 1.0 ±1.0 of range 1.5 ±1.5 of range 2.5 ±2.5 of range

　　5.4 The hysteresis of the hysteresis thermometer should not be greater than the maximum value of the basic error limit.

　　5.5 Repeatability The repeatability of the thermometer should not be greater than one-half of the basic error limit****** value.

　　5.6 The detection element of the thermal stability thermometer shall still meet the requirements of Article 5.3 after the upper limit of measurement is maintained for the time specified in Table 6. Table 6 Measurement upper limit ℃ Holding time h ≤300 24 400 12 500 4 5.7 Time constant The time constant of the thermometer should not be greater than 40s.

　　5.8 Vibration resistance thermometer should be able to withstand a vibration resistance test with a frequency of 25Hz, a displacement amplitude of 0.6mm, and a sine wave of vibration waveform, for a total of 24h. After the test, the thirst meter should still meet the requirements of Article 5.3 without mechanical damage.

　　5.9 Position Affects The indication value change caused by the thermometer tilted forward, backward, left and right 90° from the reference working position should not exceed the maximum value of the basic error limit.

　　 5.10 The sheath of the pressure thermometer shall be able to withstand the pressure test of 1.5 times the nominal pressure without damage and leakage.

5.11 Basic environmental conditions for transportation, transportation and storage The thermometer with factory packaging should be able to withstand high temperature (+55℃), low temperature (-40℃), continuous shock (acceleration: 98m/s2, pulse duration: 11ms) and Free fall (height: 250mm) test. After the test, it should still meet the requirements of 5.2, 5.3, 5.4 and 5.5.

6. Test method

　　6.1 Appearance, structure and assembly quality inspection shall be inspected with visual inspection method and corresponding tools in accordance with 5.2 requirements.

6.2 Basic error limit test 6.2.1 Test conditions a. The ambient temperature is 15～35℃, the relative temperature is 45%～75%, and the atmospheric pressure is 86kPa～106kPa; b. The insertion length of the thermometer should meet the requirements of the product manual ; c. No bumps and vibrations. 6.2.2 Test equipment and standard instrument The test equipment is a constant temperature bath, and the standard instrument is a standard thermometer. When measuring the temperature of the constant temperature bath, the limit error of the measuring method used should not be more than one quarter of the basic error limit of the tested thermometer.