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Thermocouple Compensation Wire Classification and Technical Requirements
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1. Classification of Compensation Wires
1.1 Tolerance Level and Usage Conditions
Compensation wires are categorized based on the tolerance of their thermoelectric characteristics into two types: standard temperature and high-temperature grades. These classifications help ensure proper application in different environments, offering varying levels of accuracy and durability.
1.2 Structural Forms
1.2.1 Core Types
The core of a compensation wire can be either single-strand or multi-strand, depending on the application requirements. The number of strands is specified in Table 2 for reference during selection and installation.
1.2.2 Insulation, Sheath, and Shielding
The insulation layer and sheath are typically made from polyvinyl chloride (PVC) for general use. For heat-resistant compensation wires, materials such as polytetrafluoroethylene (PTFE) are used for insulation, while the sheath may be made of PTFE or alkali-free glass fiber. These materials are coated with silicone or PTFE dispersion paint to enhance performance under extreme conditions.
Shielding layers are usually composed of tinned copper wire, galvanized steel wire, or composite aluminum (copper) tape, providing electromagnetic interference protection and ensuring signal integrity.
2 , Technical Specifications
2.1 Insulation, Sheath, and Shielding
2.1.1 Dimensions and Tolerances
The thickness of the core insulation, sheath, and maximum outer diameter must comply with the specifications outlined in Table 4. These dimensions ensure structural integrity and compliance with industry standards.
2.1.2 Insulation Layer
The insulation layer should be smooth, uniform in color, and free of mechanical damage. Its thickness tolerance is -10% of the nominal value, with the thinnest point not less than 90% of the nominal value minus 0.1 mm. The insulation must withstand a 4000V AC spark test at 50Hz without breakdown, ensuring electrical safety.
For heat-resistant compensation wires, the insulation thickness tolerance is -20%, with the thinnest part not less than 90% of the nominal value minus 0.1 mm. The outer diameter may have slight variations but must remain within the specified limits.
2.1.3 Sheath
The sheath should be tightly wrapped around the insulation layer, with no adhesion between the insulation and sheath. It should be smooth, even in color, and have a thickness tolerance of -20%. For glass wool sheaths, the weaving density must be at least 90%.
2.1.4 Shielding Layer
The shielding layer must have a weaving density of at least 80%, with any broken ends trimmed after connection. The composite aluminum (copper) tape should adhere closely to the insulation layer and not loosen easily. The shielding thickness should not exceed 0.8 mm.
2.2 Insulation Resistance
Under ambient temperatures of 15–35°C and humidity below 80%, the insulation resistance between cores and between the core and shield must be at least 5 MΩ per 10 meters, ensuring reliable electrical performance.
2.3 Physical and Mechanical Properties
The physical and aging properties of the insulation and sheath must meet the requirements listed in Table 5, ensuring long-term reliability and performance under various conditions.
2.4 Heat Resistance
Heat-resistant compensation wires must undergo a 24-hour heat resistance test at 220±5°C. After bending 180° around a cylinder five times its diameter, there should be no cracks, and the insulation resistance between the core and shield must be at least 25 MΩ per meter.
2.5 Moisture Resistance
These wires must withstand 40±2°C and 95±3% humidity for 24 hours. After testing, the insulation resistance between the core and shield should not drop below 25 MΩ, ensuring continued functionality in humid environments.
2.6 Low Temperature Performance
Generally, compensation wires should be tested at -20°C to evaluate their low-temperature winding performance. The insulation layer should show no cracks when wound on the test bar, confirming flexibility and durability in cold conditions.