In the field of industrial temperature measurement, the dual-sheath mounted junction box type platinum resistance thermometer, with its unique double-layer protective tube structure and modular design, has become a core temperature measurement component in high-temperature, high-pressure, and highly corrosive fluid environments. Its function is not only reflected in precise temperature monitoring, but also in the comprehensive improvement of sealing, anti-interference, and ease of maintenance through structural innovation, providing reliable technical support for complex working conditions.
I. Core Function: The Integration of Precise Temperature Measurement and Multiple Protection
The core function of the dual-sheath mounted junction box type platinum resistance thermometer is to provide high-precision temperature measurement in extreme environments, while simultaneously achieving dual protection of physical protection and signal isolation through the double-layer protective tube design. Its temperature measurement principle is based on the resistance-temperature characteristics of platinum resistance; the resistance value of the platinum wire changes linearly with temperature, and is converted into an electrical signal output through a bridge circuit. The dual-sheath structure consists of an inner protective tube (316L stainless steel or Inconel 625) and an outer protective tube (carbon steel or alloy steel), with a high-purity magnesium oxide (MgO) insulation layer in between, effectively isolating heat conduction and reducing the impact of ambient temperature on measurement accuracy. This design allows the sensor to maintain an accuracy of ±0.15℃ (Class A) or ±0.3℃ (Class B) over a wide temperature range of -200℃ to 600℃, meeting the stringent requirements of industrial temperature measurement.
II. Structural Advantages: Balancing Sealing, Anti-interference, and Ease of Maintenance
Sealing and Mechanical Strength
The dual-sheath design achieves rigid fixation through flange connection (e.g., DN25 PN1.6), with the inner protective tube directly contacting the medium and the outer protective tube providing additional mechanical support. This structure effectively prevents medium leakage and sensor loosening in high-temperature, high-pressure (e.g., 10 MPa steam pressure) or high-vibration environments. For example, in cracking furnaces in the petrochemical industry, the dual-sheath can withstand the dual challenges of 850℃ high temperature and mechanical stress, ensuring long-term stable operation.
Electromagnetic Interference Resistance
The junction box is made of die-cast aluminum alloy or flame-retardant engineering plastic, with a protection rating of IP65, and features ceramic or mica insulated terminals internally, supporting three-wire or four-wire connections. The Faraday cage effect is achieved through grounding bolts, shielding against external electromagnetic interference and ensuring stable signal transmission. In the cooling systems of nuclear power plants in the power industry, this design prevents electromagnetic noise from interfering with temperature readings, guaranteeing data reliability in extreme environments.
Convenient Maintenance
The junction box and protective tube adopt a modular design, allowing for separation without compromising the seal. During maintenance, only the probe needs to be replaced, while the junction box, cables, and other components can be reused, significantly reducing long-term operating and maintenance costs. For example, in sterilization equipment in the food processing industry, the frequent CIP (Cleaning-in-Place) requirements are efficiently met through the double-tube design, greatly reducing maintenance downtime.
III. Application Scenarios: A Reliable Choice in Extreme Environments
Double-tube mounted junction box type platinum resistance thermometers are widely used in high-temperature, high-pressure, and highly corrosive fluid environments, where their advantages are particularly prominent:
Petrochemical Industry: In cracking furnaces and hydrogenation reactors, the double tube withstands high-temperature steam pressure and mechanical vibration, ensuring the continuity of temperature monitoring and preventing process interruptions caused by sensor failure.
Power Industry: Nuclear power plant cooling systems utilize its radiation resistance to provide long-term stable temperature data under extreme temperatures and pressures, providing critical support for safe operation.
Metallurgical Industry: In molten metal monitoring, the rigidity and sealing of the double tube protect the platinum resistance thermometer from corrosion by highly corrosive media, ensuring production safety.
IV. Technical Parameters and Selection Suggestions
The main technical parameters of the double-tube mounted junction box type platinum resistance thermometer include temperature measurement range (-200℃ to 600℃), accuracy class (Class A or Class B), thermal response time (≤45 seconds), and protection class (IP65). When selecting, the flange specifications, protective tube material, and wiring method should be chosen according to the working conditions. For example, in highly corrosive environments, Inconel 625 material protective tubes should be prioritized; in scenarios requiring high-precision measurement, a four-wire connection method should be used to eliminate the influence of lead resistance.
V. Summary: The Ultimate Embodiment of Engineering Value
The double-tube mounted junction box type platinum resistance thermometer achieves a perfect balance between reliable sealing and convenient maintenance through its double-layer protective tube structure and modular design. Its function lies not only in providing accurate temperature monitoring, but also in overcoming technical challenges in extreme environments through structural innovation. This design makes it an ideal choice for high-temperature, high-pressure, and highly corrosive fluid environments, providing an efficient and stable temperature monitoring solution for complex operating conditions. Understanding and applying these design features can achieve maximum reliability at minimum cost, bringing significant economic and technical benefits to the field of industrial temperature measurement.
