In the field of industrial temperature measurement, fixed flange-mounted junction box type platinum resistance thermometers and metal tube probe insertion type junction box platinum resistance thermometers are two common sensor types. 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 Sealing vs. Modular Insertion
The core of the fixed flange-mounted junction box type platinum resistance thermometer lies in its rigid, integrated structure. Its design features include:
Flange Integration: The end of the protective tube is welded or integrally formed with a flange (such as DN25 PN1.6 or DN50 PN10). The flange face is flat or convex/concave, matching graphite or metal spiral wound gaskets for sealing. The junction box and protective tube are inseparable, usually made of cast aluminum or stainless steel, with an IP65 protection rating, and internal terminals supporting three-wire or four-wire connections.
Sealing Mechanism: Relies on compression sealing between the flange face and the gasket, with no moving connection points, resulting in high overall rigidity and excellent resistance to vibration and thermal stress, suitable for high-pressure environments.
Thermal Response Characteristics: The thermal conductivity of the metal protective tube and flange optimizes heat transfer, resulting in a relatively fast response time, suitable for scenarios requiring stable monitoring.
The metal tube probe insertion type junction box platinum resistance thermometer adopts a modular insertion design, with the following structural characteristics:
Independent Probe: The metal protective tube (such as 316L stainless steel) acts as the probe, directly inserted into the junction box via threads or clips, forming a separable electrical interface. The junction box is made of die-cast aluminum alloy or engineering plastic, with an IP65 protection rating, and internal ceramic or mica insulated terminals supporting three-wire or four-wire connections.
Sealing Method: The connection between the probe and the junction box uses a metal gasket or fluororubber O-ring seal to prevent media leakage, but the probe can be replaced online during maintenance.
Thermal Response Characteristics: The probe insertion depth affects the heat transfer efficiency, resulting in a slightly slower response time than the flange type, but the modular design facilitates quick maintenance.
II. Installation Methods: Flange Mounting vs. Probe Insertion
The installation steps for flange-mounted sensors include:
Flange installation: Weld or bolt the flange connector to the equipment or pipeline, ensuring the flange surface is flat and free of deformation.
Sensor fixing: Fix the sensor to the connector using flange bolts. After manual pre-tightening, tighten with a torque wrench to the specified torque (e.g., 80–120 N·m for DN25 PN1.6).
Junction box connection: The junction box is integrated with the protective tube, eliminating the need for additional wiring steps; it connects directly to the display instrument.
Power-on inspection: Measure the sensor resistance to confirm there are no short circuits or open circuits, and check for single-point grounding of the shielding layer.
The installation steps for metal tube probe insertion include:
Equipment drilling: Drill and tap a hole in the equipment or pipeline to match the probe thread specifications (e.g., M20×1.5).
Probe insertion: Screw the probe into the threaded hole. After manual pre-tightening, re-tighten with a torque wrench to 1.5–2.5 N·m.
Junction box installation: The junction box is installed independently and connected to the probe via threads or clips, ensuring the electrical interface is separate.
Power-on commissioning: Connect to the display instrument, observe whether the temperature reading is stable, and check the wiring security.
III. Application Scenarios: High-Pressure Heavy Industry vs. Medium-to-Low Pressure Flexible Scenarios
Flange-mounted sensors are suitable for high-pressure, high-temperature, and highly corrosive environments, such as:
Cracking furnaces and hydrogenation reactors in the petrochemical industry, requiring resistance to 10–20 MPa pressure and strong vibration.
Boiler heating surfaces and turbine cylinders in the power industry, with a temperature range of -200℃ to 850℃.
Cooling systems in nuclear power plants, requiring long-term reliability in extreme environments.
Metal tube probe insertion is more suitable for medium-to-low pressure scenarios requiring frequent maintenance, such as:
Sterilization equipment and fermentation tanks in the food processing industry, with a temperature range of -50℃ to 300℃ and pressure ≤6.0 MPa.
Equipment in non-sterile areas of the pharmaceutical industry, such as active pharmaceutical ingredient synthesis reactors, where online probe replacement is required. Laboratory temperature monitoring, such as for ovens and constant temperature water baths, requires low-cost and easy-to-install solutions.
IV. Maintenance Requirements: Long-Term Stability vs. Quick Replacement
The core value of fixed flange-mounted sensors lies in long-term stability:
High sealing reliability, no risk of loosening, suitable for 24/7 continuous operation, and maintenance cycles can be extended to 1-2 years.
Overall replacement results in higher operating and maintenance costs, but is suitable for "three-year inspection" scenarios, requiring shutdown, depressurization, and flange removal during maintenance.
Metal tube probe insertion type sensors prioritize ease of maintenance:
The separate design of the junction box and probe allows for partial replacement, reducing maintenance time by more than 70%, and is suitable for scenarios requiring frequent calibration.
The probe is prone to wear, and sealing performance decreases after long-term use, requiring regular inspection of the thread condition. The maintenance cycle is quarterly to semi-annually.
V. Summary: The Ultimate Trade-off of Engineering Value
Both comply with the IEC 60751 standard, but the structure defines the functional boundaries:
Fixed flange-mounted sensors are the "sturdy fortresses" of heavy industry, using an integrated design to withstand extreme environments, suitable for high-pressure, high-temperature, and highly corrosive scenarios.
Metal tube probe insertion type sensors are the "flexible guardians" of general industry, achieving convenient maintenance through modular design, suitable for medium and low-pressure scenarios requiring frequent replacement.
