The core method for determining the accuracy of a cold junction compensation module is through benchmark comparison, multi-point verification, and environmental stability testing to ensure that its temperature measurement error is controlled within ±1°C under actual operating conditions.
1. Comparison and Verification Using a High-Precision Reference Source
Ice Point Bath Method (0°C Reference): Place the thermocouple cold junction in an ice-water mixture (ensuring thorough mixing of pure water and crushed ice). The theoretical cold junction temperature is 0°C. Read the cold junction temperature displayed by the module; the deviation should be ≤ ±0.5°C.
Constant Temperature Oil Bath Method: At typical temperature points such as 25°C, 100°C, and 300°C, place the thermocouple hot junction alongside a standard platinum resistance thermometer (e.g., PT100) in a constant temperature field. Compare the module reading with the standard value; the maximum error should not exceed the module's nominal accuracy (e.g., ±1°C).
Recommended Tools: Local laboratories in Wuhan can use the FLUKE 71830 high-precision temperature field source or the ConST326 intelligent calibrator as reference equipment.
2. Real-time Dynamic Monitoring and Data Consistency Analysis
Multi-channel Consistency Test: Connect multiple thermocouples of the same type under the same temperature environment and observe whether the readings of each channel are consistent. The deviation should be <0.8°C. If individual channels drift significantly, it indicates that the compensation of that channel is abnormal.
Long-term Stability Test: Run continuously for 8–24 hours under constant temperature conditions and record the temperature fluctuation range. A high-quality module should maintain stable readings without periodic jumps or step-like drift.
Cold Junction Disturbance Response Test: Artificially heat or cool the cold junction of the module (e.g., by blowing with a warm air blower) and observe whether the compensation system can respond and correct quickly, avoiding lag or overcompensation.
3. Environmental Adaptability and Anti-interference Capability Assessment
PCB Self-Heating Effect Detection: Immediately after power-off, touch the module surface. If it is noticeably hot (>2°C of ambient temperature), cold junction sensing distortion may be caused by chip self-heating.
Electromagnetic Compatibility Test: Run the module near strong interference sources such as inverters and motors, and observe whether the temperature measurement data fluctuates or produces noise. It is recommended to use shielded compensating wires and ensure reliable grounding.
Humidity Effect Test (Wuhan Focus): Run the module in a high-temperature and high-humidity environment (such as a summer workshop) and check whether the wiring terminals are oxidized and whether the readings drift. It is recommended to select a module with an IP65 protection rating or higher.
4. Software Diagnostics and Historical Data Traceability
View Built-in Diagnostic Information: High-end modules (such as Husky Altanium™) support real-time display of parameters such as cold junction temperature, compensation voltage, and communication status. Logs can be exported and analyzed via host computer software.
Calibration Record Verification: Confirm whether the module has a traceable factory calibration certificate and that the most recent on-site calibration was within the last 6 months.
Practical Tip: Regularly use the self-test function of the MAX31855 or MAX6675 module to read the internal temperature sensor data through the SPI interface to verify its consistency with the actual ambient temperature.
