In the field of industrial temperature measurement, fixed flange-mounted junction box type platinum resistance thermometers and fixed threaded junction box type platinum resistance thermometers are two common types of temperature sensors. Despite their similar names, they differ significantly in structural design, installation method, application scenarios, and maintenance requirements. Understanding these differences is crucial for ensuring measurement accuracy, extending equipment lifespan, and optimizing maintenance costs.
I. Structural Design: Integrated Flange vs. Threaded Fixing
The core of the fixed flange-mounted junction box type platinum resistance thermometer lies in its integrated flange design. Its structure consists of a metal protective tube and a flange connection mechanism. The flange is fixed to the equipment or pipeline by welding or bolts, forming a non-removable integral structure. The protective tube is typically made of 316L stainless steel or Inconel 625, providing corrosion resistance and mechanical strength; the junction box is integrated with the protective tube, with a protection rating of IP65, and features ceramic or mica insulated terminals, supporting three-wire or four-wire connections. This design achieves sealing through a metal gasket, ensuring stability in high-pressure, high-flow, or high-vibration environments, and is suitable for applications requiring long-term fixed installation.
The fixed threaded junction box type platinum resistance thermometer, on the other hand, uses a threaded fixing design. Its structure consists of a metal protective tube and a threaded connection mechanism. The protective tube is directly fixed to the equipment or pipeline through a fixed thread (such as M20×1.5 or 1/4" NPT), forming a non-removable integral structure. The junction box is usually made of die-cast aluminum alloy or flame-retardant engineering plastic, with a protection rating of IP65. It is equipped with insulated terminals and grounding bolts to shield against electromagnetic interference. This design simplifies the installation process, reduces connection points, and thus lowers the potential risk of leakage, making it suitable for scenarios with limited space or fixed installation locations.
II. Installation Methods: Flange Fastening vs. Threaded Screw-in
The installation steps for the fixed flange mounting type include:
Flange installation: Weld or install the flange connector on the equipment or pipeline, ensuring that the flange surface is flat and free from deformation.
Sensor fixing: Fix the sensor to the connector with flange bolts. After manual pre-tightening, tighten the bolts with a torque wrench.
Junction box connection: The junction box is integrated with the protective tube and directly connected to the display instrument, eliminating the need for additional junction box installation steps.
Pre-power check: Measure the sensor resistance with a multimeter to confirm that there are no short circuits or open circuits.
The installation steps for the fixed threaded mounting type include:
Pipe drilling: Drill and tap holes according to the thread specifications, ensuring that the hole diameter matches.
Threaded connection: Screw the sensor into the threaded hole. After manual pre-tightening, tighten it to a torque of 1.5–2.5 N·m with a torque wrench.
Junction box installation: Open the junction box, connect the wires according to the color coding, and ensure single-point grounding of the shielding layer.
Power-on debugging: Connect to the display instrument and observe whether the temperature reading is stable.
III. Application Scenarios: High-Pressure Heavy Industry vs. Medium- and Low-Pressure Flexible Scenarios
The fixed flange mounting junction box type is suitable for high-pressure or frequently cleaned applications, such as:
Boiler heating surfaces and turbine cylinders in thermal power plants, which need to withstand high temperatures of 850℃ and 10 MPa steam pressure.
Cracking furnaces and hydrogenation reactors in the petrochemical industry need to withstand highly corrosive media and mechanical vibrations.
The cooling systems of nuclear power plants need to meet long-term reliability requirements in extreme environments.
Fixed threaded mounting junction box type is more suitable for scenarios with limited space or fixed installation locations, such as:
Internal temperature monitoring of small equipment or instruments where space is limited and cannot accommodate a separate junction box.
Temperature measurement for mobile equipment or temporary installations requiring quick fixing and removal.
Experimental teaching in educational institutions, used for basic temperature measurement demonstrations, requiring no complex maintenance.
IV. Maintenance Requirements: Reliability vs. Convenience
The core value of the fixed flange mounting type lies in reliability:
Flange connection provides good sealing and mechanical strength, suitable for high-pressure or frequently cleaned applications.
Overall replacement leads to higher operation and maintenance costs, but the structure is more robust and has strong vibration and impact resistance.
The fixed threaded mounting type prioritizes convenience:
Overall replacement leads to accumulating operation and maintenance costs, but the installation and maintenance process is simpler.
Threaded fixing facilitates quick installation and removal, suitable for temporary or mobile measurement scenarios.
V. Summary: The Ultimate Trade-off of Engineering Value
Both comply with the IEC 60751 Pt100 accuracy standard, but the structure defines the functional boundaries:
The fixed flange mounting type is the "sealing expert" for high-pressure cleaning, achieving high-pressure sealing through an integrated flange design, suitable for applications requiring frequent cleaning or high pressure.
The fixed threaded mounting type is the "convenient choice" for space-constrained scenarios, achieving quick fixing through an integrated design, suitable for scenarios with limited space or fixed installation locations.
