In industrial temperature measurement systems, fixed flange-mounted junction box type platinum resistance thermometers and movable threaded junction box type platinum resistance thermometers, although both belong to the junction box structure, have fundamental differences in their installation methods, sealing mechanisms, applicable scenarios, and maintenance logic. Both comply with IEC 60751 and GB/T 30121-2013 standards, but engineering selection requires precise matching based on pressure rating, maintenance frequency, and environmental severity.
I. Structural Design: Rigid Integrated vs. Modular and Detachable
The fixed flange-mounted type adopts a rigid integrated structure, with the following core features:
The end of the protective tube is welded or integrally formed with a flange (such as DN25 PN1.6, DN50 PN10), with the flange face being flat, raised, or grooved, matching standard gaskets (graphite, metal wound) for sealing;
The junction box and protective tube are an inseparable integral structure, usually made of cast aluminum or stainless steel, with an IP65 protection rating, and internal terminals supporting three-wire or four-wire connections;
There are no movable connection points, resulting in high overall rigidity and excellent resistance to vibration and thermal stress, making it suitable for high-pressure, high-temperature, and highly corrosive environments. The movable threaded installation type adopts a modular, detachable structure, with the following core features:
The end of the protective tube is machined with an external threaded interface (such as M20×1.5, G1/2"), which connects to the pre-drilled hole in the equipment via threading;
The junction box is connected to the protective tube via a movable thread and can be independently removed, allowing for "probe replacement and junction box reuse";
The junction box contains insulated terminals and a grounding bolt to shield against electromagnetic interference, making it suitable for scenarios requiring frequent calibration and sensor replacement.
II. Application Scenarios: High-Pressure Heavy Industry vs. Medium-to-Low Pressure Flexible Scenarios
|
Type |
Applicable Scenarios |
Pressure Range |
Temperature Range |
Typical Industries |
|
Fixed Flange Installation Type |
High-pressure steam pipelines, reactors, boiler heating surfaces, nuclear cooling systems |
10–40 MPa |
-200℃ to 850℃ |
Petrochemical, power generation, nuclear power, metallurgy |
|
Movable Threaded Installation Type |
Fermentation tanks, sterilization equipment, laboratory ovens, pharmaceutical reactors |
≤10 MPa |
-50℃ to 300℃ |
Food, pharmaceuticals, bioengineering, laboratories |
III. Maintainability and Reliability: Long-Term Stability vs. Quick Replacement
Fixed Flange Type:
Advantages: High sealing reliability, no risk of loosening, suitable for 24/7 continuous operation;
Disadvantages: Maintenance requires shutdown, pressure release, and flange removal, resulting in high replacement costs, suitable for "three-year inspection" scenarios.
Movable Threaded Type:
Advantages: The junction box can be independently removed, and the sensor probe can be replaced online, reducing maintenance time by more than 70%;
Disadvantages: Threads are prone to wear, and sealing performance decreases after long-term use, requiring regular inspection of the thread condition.
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IV. Core Logic of Engineering Selection
|
Selection Dimension |
Prioritize Fixed Flange Type |
Prioritize Movable Threaded Type |
|
Pressure Rating |
>10 MPa |
≤10 MPa |
|
Maintenance Frequency |
≤1 time per year |
≥1 time per quarter |
|
Space Constraints |
Spacious installation surface |
Narrow, densely packed equipment area |
|
Medium Characteristics |
High-temperature steam, corrosive fluids |
Clean liquids, no strong erosion |
|
Cost Sensitivity |
High initial cost, low long-term operation and maintenance |
Low initial cost, high replacement frequency |
Key Conclusions:
The flange type is the "system-level reliability" choice, used to ensure the safety of core processes;
The movable threaded type is the "operation and maintenance efficiency" choice, used to improve production line flexibility and response speed.
Neither is inherently superior; they simply suit different scenarios. Choosing the wrong type will lead to leaks, shutdowns, or excessive maintenance, at a cost far exceeding the cost of the sensor itself.
