The core of improving the accuracy of cold junction compensation in hot runner systems lies in optimizing the temperature measurement and compensation mechanism to control the error within ±0.5°C. The following are systematic improvement solutions:
1. Employ High-Precision Cold Junction Compensation Technology
Hardware-level Compensation: Using an ice-point bottle or constant temperature bath as the reference junction provides a stable 0°C baseline, suitable for laboratory calibration, with an accuracy of ±0.5°C.
Intelligent Instrument Automatic Compensation: Selecting a measuring device that supports automatic internal cold junction compensation (such as the ConST326) monitors the cold junction temperature in real time through a built-in high-precision sensor and automatically corrects the reading based on the thermocouple type.
External Platinum Resistance Compensation: Connecting a high-precision resistance sensor such as a PT100 to the cold junction of the thermocouple directly measures the cold junction temperature, avoiding distortion caused by lead heat conduction.
Recommended Combination: External PT100 + Intelligent Temperature Controller, achieving dynamic compensation within ±0.5°C.
2. Optimize Sensor Layout and Signal Transmission
Multi-point Temperature Measurement Collaboration: Place multiple thermocouples at key nodes of the hot runner system (such as main runners, branch runners, and near the gate), and combine them with AI algorithms for data fusion and deviation correction.
Shielding and Isolation: Use shielded compensating wires to avoid parallel routing with power cables, reducing the impact of electromagnetic interference on weak millivolt signals.
Shortened Wire Length: Control the length of compensating wires to within 50 meters to prevent signal attenuation; if the distance is too long, it is recommended to use a temperature transmitter to convert the millivolt signal to a 4–20mA standard signal for transmission.
3. Systematic Calibration and Maintenance
Regular Calibration: Perform a comprehensive calibration of thermocouples, compensating wires, and temperature control modules every 3–6 months to prevent drift caused by long-term use.
Cold Junction Environment Control: Place the cold junction area in a constant temperature, dry, and vibration-free environment to avoid temperature fluctuations caused by uneven air convection or PCB self-heating.
Connection Reliability Guarantee: Ensure the thermocouple and compensating wires are correctly connected (red indicates positive). Ensure the joints are waterproofed and protected against oxidation to prevent poor contact from introducing additional thermoelectric potential.
Practical Tip: In Wuhan, where temperatures and humidity are high, it is recommended to check the terminals for moisture and oxidation monthly. If necessary, install a moisture-proof box.
