Structural Differences: The movable threaded connection type thermocouple consists of three parts: an independent, detachable metal protective tube, a rotating threaded interface with sealing function, and a sealed junction box. The thermoelements are insulated from the protective tube by insulating material, and the signal is led out through the junction box terminals, achieving both mechanical and electrical separation. In contrast, the Teflon-sheathed corrosion-resistant thermocouple has an integrated, junction-box-free structure. The thermoelements are directly encased in a single, sintered polytetrafluoroethylene (PTFE) sheath, and the leads are directly routed out using PTFE insulated wires. There are no independent wiring units, resulting in a highly integrated, non-separable structure; it is a consumable design where the probe is the entire unit.
Installation Method and Operation Logic: The movable threaded type requires manual screwing into a threaded hole. After installation, the sensing end can still be micro-adjusted 360° to adapt to curved pipe walls, spatial interference, or installation deviations, relying on torque control to ensure sealing. The Teflon-sheathed type uses a direct insertion or clamping method, usually directly inserted into corrosive media pipes or containers. It relies on the flexibility of the sheath to conform to the inner wall, requiring no rotation, making operation extremely simple. However, it completely relies on the accuracy of contact with the medium, cannot correct positional deviations, and cannot be adjusted after installation.
Maintenance and Replacement Capabilities: The movable threaded type allows for the replacement of only the protective tube and sensing probe; the junction box, cable, and seals can be reused for a long time. Single maintenance takes 5-10 minutes, suitable for periodic calibration and fault replacement. For the Teflon-sheathed type, once the sheath is worn, aged, or the thermoelement fails, the entire probe must be scrapped and replaced. There are no detachable parts, making it a disposable or consumable design with high maintenance costs and no repairability.
Environmental Adaptability and Reliability: The movable threaded type, with its metal protective tube and sealed junction box, can withstand high temperatures, high pressure, strong vibrations, condensation, and cleaning environments, making it suitable for continuously operating industrial systems. Although the Teflon-sheathed type offers excellent chemical corrosion resistance (resistant to strong acids, strong bases, and organic solvents), it has low mechanical strength, is not impact-resistant, and is not vibration-resistant. Its temperature limit is typically ≤260℃, and long-term use can easily lead to sheath cracking due to thermal cycling or fluid erosion. It is only suitable for medium-low temperature, static or low-flow corrosive media environments, such as electroplating tanks, chemical reactor linings, and battery electrolyte monitoring.
Typical Application Scenarios: The movable threaded type is widely used in demanding environments requiring long-term operation, maintainability, and compliance with industrial standards, such as pharmaceutical GMP reactors, food CIP cleaning lines, nuclear power auxiliary systems, and high-vibration pumping stations. The Teflon-sheathed type is primarily used in scenarios requiring extremely high chemical resistance but very low mechanical stress, such as electroplating plants, battery factories, chemical acid and alkali pipelines, and laboratory corrosive solution temperature measurement.
Standards and Specifications: The movable threaded type strictly adheres to GB/T 30429-2013 "Replaceable Sheath" and IEC 60584-3 "Removable Installation" specifications, possessing standardized interfaces and traceability. The Teflon-sheathed type lacks a unified industrial installation standard and relies on manufacturer-defined structural designs, classified as "non-standard anti-corrosion temperature sensing elements." Its performance parameters (such as sheath thickness and sintering process) depend on the manufacturer's process level and do not have universal interchangeability.
Core Selection Decision: If long-term stable operation, repeatable maintenance, vibration resistance, and compliance with industrial standards are required, the movable threaded type must be selected. If only strong corrosive media resistance is needed, without disassembly, at moderate temperatures, and without mechanical disturbance, the Teflon-sheathed type is an economical and efficient anti-corrosion solution.
Operating Precautions: For threaded connectors, forcible insertion or removal of the junction box or using power tools to forcibly rotate it is strictly prohibited, as this will damage the decoupling structure; for Teflon-sheathed connectors, they must not be used in high-temperature, high-pressure, severely vibrating, or fluid-flushing environments, and the leads must not be bent, pulled, or come into contact with metal conductors, otherwise it will lead to insulation failure, signal drift, or sheath rupture.
