Tech Docs
FAQType C thermocouple compensation wire
Type C thermocouple compensation leads (usually marked CX) are signal transmission lines specifically designed for tungsten-rhenium high-temperature thermocouples. Because Type C thermocouples are made of extremely expensive and brittle rare metals (95% W/5% Re for the positive electrode and 74% W/26% Re for the negative electrode), their extension leads do not use the original thermocouple material. Instead, they employ a specially formulated low-grade metal compensation alloy (such as Hoskins 405/426 nickel-based alloy) to simulate the same thermoelectric properties as a Type C thermocouple within a specified temperature range.
Core Specifications and Technical Features
| Project | Specifications and Instructions |
|---|---|
| Corresponding graduation number | Type C thermocouple (measuring limit up to 2315°C) |
| Wire code | CX (C represents compensating alloy, X represents extension/compensation application) |
| Compensation materials | Commonly used Hoskins 405 (positive electrode) / 426 (negative electrode) nickel-based alloys |
| Precision temperature range | The thermoelectric potential error is minimized between ambient temperatures of 0°C and 200°C (32°F ~ 392°F). |
| Tolerance for error | In extended testing from 0°C to 870°C, the electromotive force error was within approximately ±0.110 mV. |
| Commonly used insulating outer covering | Teflon (FEP/PFA) (temperature resistance 200~260°C) or fiberglass (temperature resistance up to 480°C) |
| ANSI standard colors | Positive electrode: White | Negative electrode: Red | Outer coating: Orange (or white with red stripes) |
The core advantages of using compensation wires (CX)
- Significantly reduced costs: Using tungsten iron wire for long-distance cable laying would be extremely expensive. CX cables use low-metal simulation, saving a huge amount of material costs.
- Improved mechanical strength and toughness: Tungsten-iron alloys are very fragile and easily break due to machine vibration and repeated bending. CX compensation wires have excellent ductility and resistance to shock and mechanical stress.
- Excellent oxidation resistance: Type C thermocouples are easily oxidized at high temperatures, while the nickel-based alloy used in CX wires has very good oxidation protection at room temperature and medium temperature.
Usage and Selection Precautions
- Do not exceed the operating temperature: The ambient temperature of the compensation conductor connectors and wiring should not exceed 200°C (the upper limit depends on the outer sheath material). Once the compensation conductor itself is exposed to an environment with excessively high temperatures, its thermoelectric characteristics will deviate from the original C-curve, causing a significant increase in measurement error (potentially exceeding 0.100 mV).
- Polarity must not be reversed: When connecting temperature measuring instruments (such as PLCs and displays), the positive and negative poles (white for positive, red for negative) must be strictly followed. Reversing the polarity will result in completely incorrect temperature data.
- Ordinary copper wires should not be used: If ordinary wires or other forms of compensation wires such as K-Type are used directly, additional parasitic thermoelectric potential will be generated at the connection point, which will compromise the accuracy of high-temperature measurements.
