What is the function of a screw-type thermocouple

Core Temperature Measurement Function

The screw-type thermocouple is based on the Seebeck effect, utilizing two different metal alloys (such as K-type nickel-chromium/nickel-silicon) to generate a thermoelectric potential difference at the measuring end. This directly converts temperature changes into microvolt-level electrical signals, which are then linearized by the instrument to output accurate temperature values. Its essence is direct contact temperature sensing, requiring no medium for heat conduction, resulting in extremely fast response times, making it suitable for transient temperature monitoring scenarios.

 

Structural Design and its Enhancement Mechanisms

Threaded Rigid Connection: The external thread (e.g., M27×2) screws into the pre-drilled hole in the equipment, achieving a tight metal-to-metal contact. This significantly reduces thermal resistance, ensuring the hot end synchronizes with the temperature field of the measured object, improving measurement accuracy (error controllable within ±1℃).

Magnesium Oxide Insulation Layer: Filled inside the protective tube, it ensures high insulation resistance (≥100MΩ) while promoting heat conduction and preventing signal drift.

Protective Tube Material Adaptation: The 304/316L stainless steel tube body combines corrosion resistance and thermal conductivity, making it suitable for hygienic environments such as chemical and food processing, preventing contamination of the medium.

 

Typical Industrial Application Scenarios

Industry	Application Location	Function Description
Injection Molding	Barrel, Nozzle	Real-time monitoring of melt temperature to prevent overheating degradation or cold material blockage, ensuring dimensional stability of products.
Heat Treatment Furnace	Furnace Door, Fixtures	Capturing workpiece surface temperature curves to ensure accurate execution of quenching and tempering process parameters
Chemical Pipelines	Reactor Outlet, Heat Exchanger Bypass	Monitoring fluid temperature fluctuations, assisting PID control of reaction rate, and avoiding side reactions.
Food and Pharmaceutical	Sterilizer, Filling Lines	Complies with GMP requirements, achieving temperature measurement without dead zones, ensuring sterilization temperature meets standards (e.g., 121℃).
Power Auxiliary Equipment	Fan Bearing Housing, Transformer Oil Tank	Preventing overheating failures, enabling condition monitoring and predictive maintenance.

 

Core Advantages and Limitations

Advantages:

Easy Installation: No flange welding required, only pre-fabricated threaded holes are needed, saving over 50% of installation time.

High Maintainability: Can be quickly disassembled and replaced in case of failure without affecting the overall system operation.

High Cost-Effectiveness: Unit temperature measurement point cost is 40%~60% lower than flange type, suitable for dense deployment.

Limitations (Inapplicable Scenarios):

High-Pressure Systems (>10MPa): Threaded seals are prone to leakage and cannot replace the face-sealing structure of flanges.

High Vibration Environments (e.g., large compressors, arc furnaces): Threads are prone to loosening, leading to poor contact or breakage.

Large-Diameter Pipelines (>DN50): Thread size is limited and cannot match mainstream industrial pipe diameters.

Highly Corrosive Media (e.g., concentrated hydrochloric acid, molten sulfur): The thread root is easily corroded, leading to jamming and failure.

 

Essential Differences from Flange Type

Threaded thermocouples are an "economical, rapid deployment" temperature measurement solution, focusing on scenarios with medium-low pressure, small diameter, and prioritized maintainability; while flange type is a "high reliability, high safety" industrial-grade solution, suitable for core process nodes with high pressure, large diameter, and continuous operation. These two are not substitutes for each other, but rather a functional and complementary configuration of temperature measurement levels.

The core value of screw-type thermocouples lies in: achieving accurate, fast, and repeatable temperature acquisition at critical process points with the lowest installation cost. They are an indispensable basic sensing unit for achieving automated and intelligent temperature control in modern process industries.