Structural Differences: The movable threaded connection type thermocouple uses a rotatable threaded interface, with a mechanical decoupling structure between the protective tube and the junction box, allowing for physical separation of the probe and the wiring unit, supporting independent removal and angle adjustment; while the connecting tube type probe thermocouple is a rigid, integrated structure, where the protective tube is rigidly connected to the junction box or mounting flange through welding, fixed threads, or flanges, with no rotational or removal freedom. The probe and wiring system form an inseparable whole, representing a typical "fixed sheath" design.
Installation Method and Operation Logic: The movable threaded type supports "install first, then adjust"-after screwing into the threaded hole, the probe can still be rotated 360°, precisely fitting against pipe walls, curved surfaces, or confined spaces, accommodating installation deviations without requiring high-precision pre-processing; the connecting tube type requires "one-time positioning," ensuring the probe axis is perfectly aligned with the temperature measurement point during installation. This typically relies on welding or rigid thread locking, and any angular deviation cannot be corrected afterward, requiring extremely high precision in equipment manufacturing and construction techniques.
Maintenance and Replacement Capabilities: For the movable threaded type, maintenance only requires unscrewing and replacing the protective tube and temperature sensing probe. The junction box, cable, and seals can be reused for a long time, with each operation taking only 5-10 minutes, significantly reducing downtime costs; for the connecting tube type, if the probe is damaged, aged, or the seal fails, the entire unit must be removed, involving downtime, pressure release, weld cutting, or flange disassembly. Maintenance takes several hours, and can easily damage the equipment's sealing surface, lacking the ability to independently replace the probe.
Stress Resistance and Environmental Adaptability: The movable threaded type, due to its elastic micro-adjustment capability, effectively absorbs dynamic stresses such as thermal expansion and contraction, pump vibration, and fluid pulsation, significantly reducing the risk of protective tube fracture or thread fatigue failure. It is suitable for high-vibration and frequent start-stop operating conditions. The type with a connecting pipe features a rigid connection; long-term exposure to thermal cycling and mechanical stress can easily lead to weld cracking, metal fatigue, or sealing surface deformation. However, its overall structural strength is high and its sealing performance is excellent, making it specifically designed for high-temperature, high-pressure, highly corrosive, and long-term continuous operation environments, such as boiler furnaces, molten salt pipelines, and nuclear power main circuits.
Typical Application Scenarios: The movable threaded type is widely used in industrial scenarios requiring frequent calibration, clean operation, and complex spatial arrangements, such as pharmaceutical GMP reactors, food CIP cleaning lines, biological fermentation tanks, and high-vibration pumping stations. The type with a connecting pipe is primarily used in critical temperature measurement points in heavy industries with stringent requirements for sealing, structural strength, and long-term stability, such as petrochemical cracking furnaces, thermal power boilers, chemical high-pressure reactors, and nuclear power steam generators.
Standards and Normative Compliance: The movable threaded type strictly conforms to the definition of "replaceable sheath" in GB/T 30429-2013 and the "removable installation" category in IEC 60584-3; the type with a connecting pipe is classified as a "fixed sheath" or "permanent installation" structure, and its design and manufacturing are based on the technical requirements for "non-removable thermocouples" in JB/T 5582-2014. These two types represent completely different technical approaches within the standard system.
Core Selection Decision:If the application emphasizes maintainability, vibration resistance, clean operation, or limited space, the movable threaded type must be selected; if the pursuit is for ultimate sealing, long-term maintenance-free operation, and resistance to high pressure and high temperature, and the installation conditions are controllable, then the type with a connecting pipe is the only reliable choice.
Operating Precautions: For movable threaded types, welding or forcibly fixing the junction box is strictly prohibited, as this will completely negate its core advantages; for types with connecting tubes, forcibly rotating or disassembling the probe is prohibited, as this will damage the welded seal or thread integrity, leading to media leakage or safety hazards.
