In the field of industrial temperature measurement, fixed flange-mounted junction box type platinum resistance thermometers and PTFE-sheathed corrosion-resistant platinum resistance thermometers are two types of temperature sensors designed for different operating conditions. Although both are based on the platinum resistance principle, they differ fundamentally in structural design, corrosion protection mechanisms, application scenarios, and maintenance procedures. Understanding these differences is crucial for ensuring measurement accuracy, extending equipment lifespan, and optimizing operation and maintenance costs.
I. Structural Design: Flange Rigid Sealing vs. PTFE Flexible Isolation
The fixed flange-mounted junction box type platinum resistance thermometer adopts a rigid flange sealing structure, with the following core features:
Flange connection: The end of the protective tube is welded or integrally formed with a flange plate (e.g., DN25 PN1.6, DN50 PN10). The flange face is flat, raised, or grooved, matching graphite or metal spiral wound gaskets for sealing, suitable for high-pressure environments (10–40 MPa).
Integrated junction box: The junction box and protective tube are an inseparable integral structure, usually made of cast aluminum or stainless steel, with an IP65 protection rating. It has internal ceramic or mica insulated terminals, supports three-wire or four-wire connections, and achieves a Faraday cage effect through a grounding bolt to shield against electromagnetic interference.
Rigid structure: No moving connection points, strong overall rigidity, excellent resistance to vibration and thermal stress, suitable for high-temperature, high-pressure, and highly corrosive environments.
The PTFE-sheathed corrosion-resistant platinum resistance thermometer adopts a PTFE flexible isolation structure, with the following core features:
PTFE sheath: The protective tube is covered with a continuous polytetrafluoroethylene (PTFE) sheath, usually ≥1.0mm thick. Electrical spark testing (voltage 12kV, frequency 1.6×10⁶Hz) ensures no micropores, achieving complete dielectric isolation.
No independent junction box: The leads are directly routed from the end of the PTFE sheath. The structure is integrated and non-removable; maintenance requires complete replacement. Flexible Design: The PTFE sheath has extremely low surface energy and is not dissolved or swollen by any common solvents, making it suitable for extreme corrosive environments such as strong acids, strong bases, and organic solvents.
II. Corrosion Protection Mechanism: Gasket Sealing vs. Full Medium Isolation
|
Corrosion Protection Dimension |
Fixed Flange Mounting Type |
Teflon Sheath Type |
|
Acid and Alkali Resistance |
Relies on metal passivation layer, only resistant to weak acids and bases |
Resistant to strong acids (concentrated sulfuric acid, nitric acid), strong bases (NaOH, KOH) |
|
Solvent Resistance |
Easily corroded by chloride ions and halogen media |
Completely inert, not dissolved or swollen by any solvent |
|
Applicable Media |
Water, steam, edible oil, ordinary chemical liquids |
Electroplating solutions, hydrochloric acid pickling tanks, chlor-alkali reactors, semiconductor etching solutions |
|
Corrosion Protection Layer Thickness |
No additional corrosion protection layer, relies on metal wall thickness |
PTFE layer thickness ≥ 1.0mm, no micropores detected by electrical spark testing |
III. Application Scenarios: High-Pressure Heavy Industry vs. Highly Corrosive Chemical Industry
The fixed flange mounting junction box type is suitable for high-pressure, high-temperature, and highly corrosive fluid scenarios, such as:
Cracking furnaces and hydrogenation reactors in the petrochemical industry, requiring resistance to 850℃ high temperature and 10 MPa steam pressure.
Cooling systems in nuclear power plants, requiring long-term reliability in extreme environments.
Molten metal monitoring in the metallurgical industry, requiring resistance to highly corrosive media and mechanical vibration.
The Teflon sheath corrosion-resistant type is designed specifically for highly corrosive, high-purity environments, such as:
Plating tanks and pickling tanks in the electroplating industry, requiring resistance to strong acids, strong bases, and organic solvents.
Etching equipment in the semiconductor industry, requiring avoidance of metal ion contamination.
CIP (Clean-in-Place) systems in the pharmaceutical industry, requiring frequent cleaning and avoidance of media residue.
IV. Installation and Maintenance: Flange Fastening vs. Flexible Adaptation
The installation steps for the fixed flange mounting type include:
Flange welding or bolt fixing: Weld or bolt the flange plate to the equipment, ensuring the flange surface is flat and free of deformation. Sensor Mounting: The sensor is fixed to the connector using flange bolts. After manual pre-tightening, tighten with a torque wrench.
Lead Connection: Connect directly to the display instrument; no additional junction box installation is required.
Power-on and Testing: Connect to the display instrument and observe whether the temperature reading is stable.
The installation steps for the Teflon-sheathed type include:
Sheath Inspection: Ensure the PTFE sheath is undamaged and verify the absence of micropores through electrical spark testing.
Sensor Mounting: Fix the sensor to the equipment using threads or clips, avoiding excessive force that could cause the sheath to rupture.
Lead Connection: Connect directly to the display instrument; no additional junction box installation is required.
Power-on and Testing: Connect to the display instrument and observe whether the temperature reading is stable.
V. Maintenance Requirements: Periodic Inspection vs. Complete Replacement
The core maintenance of the fixed flange mounting type lies in periodically checking the flange sealing, such as:
Checking for loose flange bolts quarterly to ensure the sealing gasket is not aging.
Calibrating annually, verifying accuracy with a standard temperature source (such as an ice-water mixture).
The Teflon-sheathed type tends towards complete replacement, such as:
The sensor needs to be replaced entirely when the sheath is damaged or corroded, avoiding localized repairs.
Maintenance requires shutdown and depressurization, resulting in higher replacement costs, but it is suitable for scenarios requiring inspection every three years.
VI. Summary: The Ultimate Trade-off of Engineering Value
Both types meet the Pt100 accuracy standard of IEC 60751, but the structure defines the functional boundaries:
The fixed flange mounting type is a "sturdy fortress" for high-pressure heavy industry, achieving long-term stability through rigid flange sealing, suitable for high-pressure and high-temperature environments.
The Teflon-sheathed corrosion-resistant type is a "chemical guardian" for highly corrosive environments, resisting extreme corrosion with flexible PTFE isolation, suitable for strong acid and strong alkali environments.
