Thermometers and Temperature Sensors
In the chemical industry, temperature control is critical to ensure reaction rates, product quality, safety, and energy efficiency. Thermometers such as liquid-in-glass thermometers and bimetallic thermometers provide direct (usually mechanical) temperature readings for undemanding or crude measurements, but they are limited in measurement range, accuracy, and fragility. In contrast, temperature sensors such as thermocouples, resistance temperature detectors (RTDs), thermistors, and infrared sensors convert temperature into an electrical signal, enabling remote monitoring, data logging, and automated control. Thermocouples are rugged and have a wide measurement range; RTDs have high accuracy and stability; thermistors have high sensitivity over a narrow measurement range; and infrared sensors provide non-contact measurements. Specialized sensors such as fiber optics are suitable for harsh environments. Thermometers and temperature sensors are critical for applications such as reaction monitoring, process control, safety, quality assurance, and energy optimization in chemical processes, so they need to be carefully selected based on the application, material compatibility, explosion protection, and regular calibration.
| Device type | Classification method | Features | Application scenario |
| Liquid expansion thermometer | Classification by measurement principle | Measures temperature by using the principle that liquid (such as mercury, alcohol, etc.) expands in volume when the temperature changes. Liquid expansion thermometers have a simple structure and low cost, but their measurement range is limited. | It is widely used for temperature measurement in laboratories and industrial sites, such as measuring water temperature, oil temperature, etc. |
| Gas expansion thermometer | Classification by measurement principle | The temperature is measured by the principle that the volume of gas expands when the temperature changes. Gas expansion thermometers are usually used to measure higher temperature ranges. | Such as measuring the temperature of a high-temperature furnace. |
| Metal resistance thermometer | Classification by measurement principle | The temperature is measured by the principle that the resistance value of metal resistors (such as platinum, copper, etc.) changes when the temperature changes. Platinum resistance thermometer (Pt100) is the most commonly used one. | It is widely used in industrial automation, process control and other fields, and is suitable for medium temperature range (-200℃ to +850℃). |
| Semiconductor resistance thermometer | Classification by measurement principle | Measure temperature by using the principle that the resistance value of semiconductor materials changes when the temperature changes. Semiconductor resistance thermometers (such as thermistors) have high sensitivity. | Suitable for occasions requiring high sensitivity, such as temperature monitoring of electronic equipment. |
| Thermocouple thermometer | Classification by measurement principle | Measure temperature by using the principle that two different metals (such as copper-constantan, nickel-chromium-nickel silicon, etc.) generate thermoelectric potential when the temperature changes. Thermocouple thermometers have a wide measurement range and are suitable for high-temperature measurements. | They are widely used in high-temperature measurements in chemical, metallurgical, and electric power industries, such as boilers and reactors. |
| Radiation thermometers | Classification by measurement principle | The temperature is measured by using the intensity of infrared radiation radiated by an object at high temperature. Radiation thermometers are non-contact measurements and are suitable for high-temperature and inaccessible measurement objects. | Such as measuring molten steel temperature, furnace temperature, etc. |
| Glass thermometer | Classification by structural form | Use the expansion of liquid (such as mercury, alcohol) in the glass tube to measure temperature, with simple structure and low cost. | Widely used for temperature measurement in laboratories and industrial sites. |
| Metal protective cover thermometer | Classification by structural form | Encapsulate the temperature sensing element (such as thermocouple, thermal resistor) in a metal protective cover, which has good mechanical protection and corrosion resistance. | Applicable to temperature measurement in industrial production, especially in situations where mechanical protection is required. |
| Armored thermometer | Classified by structural form | The temperature sensing element (such as thermocouple, thermal resistor) is encapsulated in the armored tube, which has good mechanical protection and vibration resistance. | Applicable to situations where vibration resistance and mechanical protection are required, such as chemical equipment, mechanical processing, etc. |
| Literature | Author | Abstract | DOI |
| Performance Study of Thermometer Protective Sleeves | Han Jiande, Hua Xiaofeng | In view of the current application status of thermometer protective sleeves in petrochemical projects, the performance of the protective sleeves, the calculation method of vibration and the stress analysis of the protective sleeves are introduced; the causes of vibration of the protective sleeves, the natural frequency, the excitation frequency and the calculation formulas of various maximum allowable stresses are explained; the ASTMPTC 19.3-2010 on resonance, natural frequency, excitation frequency and the restrictive relationship between the two; finally, suggestions are put forward on matters that should be paid attention to in the engineering design process. | 10.3969/j.issn.1007-7324.2012.04.010 |
| Research and calculation of frequency limit of thermometer sleeve in chemical plant | Wang Yiyi | Engineering application is inseparable from temperature measurement. If the force of fluid on the thermometer sleeve is too large, it may damage the thermometer sleeve or even break it, which will cause damage to the detection element inserted in the sleeve, affect the measurement, and even cause leakage and accidents. The reasons for the resonance of the thermometer sleeve and the instantaneous amplification of dynamic stress under resonance are analyzed. Then, according to the ASME PTC 19.3 TW-2010 standard, the relationship between the vibration of the thermometer sleeve and the natural frequency f_n~c and the vortex separation frequency f_S, as well as some other restrictions, was analyzed. Finally, through the static stress and dynamic stress analysis and formula calculation of the thermometer sleeve, a more comprehensive stress analysis and fracture assessment method for the thermometer sleeve was proposed to avoid damage and fracture of the thermometer sleeve. | CNKI:SUN:YGCJ.0.2017-03-013 |
| Application of Finite Element Method in Vibration Calculation of Thermometer Sleeves | Liu Hanjie, Wang Fabing, Hu Tongyin, Li Xin | In industrial sites, the size, form and material selection of thermometer sleeves directly affect the temperature measurement effect and service life of thermocouples, thermal resistors, bimetallic thermometers, etc. Whether the sleeve can meet the vibration requirements of the site is one of the important factors affecting safe operation. Therefore, the vibration calculation of the thermometer sleeve has become the focus of bidders, designers and manufacturers. Tianjin Zhonghuan Temperature Instrument Co., Ltd. uses the finite element method to create a new method for calculating the natural frequency of the casing, making the vibration calculation more rigorous and reasonable, and has independently obtained the software copyright of the calculation program. By comparing with other existing calculation methods such as ASME, the accuracy of the calculation results of the finite element method is demonstrated. This method has a very important guiding significance for the casing specification design and on-site vibration judgment. | 10.3969/j.issn.1007-7324.2009.05.015 |
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