In the field of industrial temperature measurement, movable thread-mounted probe-type platinum resistance thermometers, fixed thread-mounted junction box type platinum resistance thermometers, and fixed flange-mounted junction box type thermocouples are three common types of temperature sensors. Although all are used for temperature monitoring, they have significant differences in structural design, working principles, and application scenarios.
I. Movable Thread-Mounted Probe-Type Platinum Resistance Thermometer
The core of the movable thread-mounted probe-type platinum resistance thermometer lies in its temperature-sensing element-a platinum resistor (such as Pt100 or Pt1000) directly encapsulated at the end of a metal protective tube, forming a probe structure. This design allows for flexible installation and removal by directly engaging with threaded holes on the equipment wall using a rotatable thread (such as M8, M12). Its advantages include high accuracy (Class A can reach ±0.15℃), good long-term stability, and vibration resistance, making it suitable for high-precision temperature measurement in medium and low temperature ranges (-200℃~850℃) in chemical reactors, laboratory calibration, and medical sterilization equipment.
Working Principle
Platinum resistance thermometers measure temperature based on the linear change of resistance with temperature. The temperature-sensing element is placed at the tip of a slender metal probe, connected to a display instrument or control system via a cable at the tail. When in use, the probe is directly inserted into the environment to be measured, resulting in a short heat conduction path and fast response speed. The movable thread design allows the sensor to closely fit the surface of the measured medium during installation, ensuring measurement accuracy.
Application Scenarios
Movable thread-mounted probe-type platinum resistance thermometers are particularly suitable for applications requiring frequent calibration or replacement. For example, in laboratories, researchers may need to regularly adjust or replace sensors to adapt to different experimental conditions. Furthermore, its high accuracy and stability make it an ideal choice for temperature monitoring in medical equipment.
II. Fixed Thread-Mounted Junction Box Type Platinum Resistance Thermometer
The fixed thread-mounted junction box type platinum resistance thermometer is similar in structure to the movable thread-mounted probe-type platinum resistance thermometer, but the key difference is that its temperature-sensing element is physically separated from the electrical connection terminals. The probe is fixed to the temperature measurement point via a threaded connection, while the junction box is independently mounted on the outside of the equipment and connected via wires. The junction box typically has an IP65 or higher protection rating, is internally sealed against moisture and explosion-proof, and is suitable for industrial environments that are flammable, explosive, high-humidity, or require centralized wiring.
Working Principle
Similar to the movable threaded probe-type platinum resistance thermometer, the fixed threaded junction box-type platinum resistance thermometer also relies on changes in resistance value for temperature measurement. However, due to the thermal inertia of the wires, its response speed is slightly slower than that of the probe type. It offers stronger electrical isolation, facilitating maintenance and signal transmission.
Application Scenarios
This type of sensor is particularly suitable for systems requiring remote signal acquisition or explosion-proof certification. For example, in oil tank areas or pharmaceutical clean rooms, safety and reliability are paramount. The fixed threaded design ensures stable operation in harsh environments, while the independent mounting of the junction box simplifies maintenance and signal transmission.
III. Fixed Flange Mounted Junction Box Type Thermocouple
The fixed flange mounted junction box type thermocouple is based on the Seebeck effect, consisting of two different metal wires (such as nickel-chromium and nickel-silicon for K-type) welded together to form the measuring end, encapsulated in a metal protective tube, and directly locked to the equipment surface via a fixed flange (such as a DN50 flange). Its greatest advantages are its wide temperature range (0℃~1300℃), fast response (thermal response time ≤40 seconds), and self-generating characteristics without the need for external power supply, making it suitable for high-temperature, high-pressure, or industrial environments requiring frequent disassembly.
Working Principle
The thermocouple relies on the thermoelectric potential generated by the temperature difference for temperature measurement. Its compact structure ensures close contact with the measured surface through the fixed flange, ensuring efficient heat conduction. The accuracy is usually lower than that of platinum resistance thermometers (mostly Class II ±1.5℃), and it requires a cold junction compensation circuit for temperature calculation.
Application Scenarios
Fixed flange mounted junction box type thermocouples are widely used in applications requiring fast response and wide temperature range measurement, such as power plant boilers and petrochemical equipment in high-temperature environments. Its fixed flange design allows for stable operation in high-pressure or frequently disassembled applications, and is particularly suitable for pipes or containers where threading is not possible. Summary
The movable threaded probe-type platinum resistance thermometer, the fixed threaded junction box-type platinum resistance thermometer, and the fixed flange-mounted junction box-type thermocouple each have unique characteristics in terms of structural design, working principle, and application scenarios. The movable threaded probe-type platinum resistance thermometer is suitable for applications requiring high precision and flexibility; the fixed threaded junction box-type platinum resistance thermometer is suitable for environments requiring safety and remote signal acquisition; while the fixed flange-mounted junction box-type thermocouple is designed specifically for high-temperature, high-pressure, and frequent disassembly requirements. When making a selection, factors such as temperature range, accuracy requirements, environmental protection rating, ease of installation, and maintenance frequency should be considered to ensure optimal performance. By understanding the core differences between these three types of sensors, users can more effectively choose the temperature sensor best suited to their specific application.
