I. Preparation Prior to Calibration
Tools List: Copper fine-tuning set screw, high-precision digital vernier calliper, standard gauge block, and Grade 0 feeler gauge. Includes data acquisition host computer.
Prerequisites: The hot runner system must be completely cooled to room temperature (25°C). The sensor must be fastened and installed in its designated location. To guarantee a consistent output signal, activate the device and allow it to warm up for 15 minutes.
II. Cold-State Two-Point Basic Calibration
Zero-point Calibration: Apply pressure to the hot runner plate to achieve its initial zero position. Confirm that the sensor probe is entirely flush with the hot runner plate without any gaps by employing a feeler gauge. In the host computer, adjust the present displacement value to 0mm.
Full-scale Calibration: Position a standard gauge block between the heated runner plate and the sensor probe. The gauge block's thickness should correspond to the sensor's predetermined full-scale displacement value. Adjust the current output value to the standard gauge block thickness in the host computer.
Linearity Verification: Select three intermediate points that are equitably spaced between 0 and full scale. Use a feeler gauge to compare the sensor output values with the measured displacement values. Verify that the linearity error is less than or equal to 0.1mm. Readjust the zero point and full scale coefficients if the value exceeds the range.
III. Hot Dynamic Calibration: Begin the segmented heating program of the hot runner, increasing the temperature by 50℃ every 30 minutes. At the same time, document the measured displacement values of the sensor at various temperature stations.
Contrast the measured values with the theoretically calculated value of thermal expansion, ΔL = L × α × ΔT. Fine-tune the sensor's coaxiality to eradicate systematic errors caused by installation misalignment if the deviation exceeds 0.2mm.
Hold the sensor output displacement value for one hour after heating to the operating temperature to verify that it is stable and drift-free, with zero drift controlled within 0.05mm.
IV. Alarm Threshold Calibration
Adjust the displacement over-limit alarm threshold in accordance with the safety expansion clearance specified in the hot runner design. In order to initiate an early warning, the threshold is established at 90% of the safety clearance.
Confirm that the system can trigger the existing audible and visual alarms within 1 second and simultaneously output an interlock warning signal to the temperature control system by manually simulating a displacement error scenario.
V. Verification of Post-Calibration
Confirm that the sensor's repeatability error is ≤0.05mm and that there are no skipped or missing data after three consecutive full-stroke forward and reverse movement testing..
Generate a calibration report by recording all calibration data. Afterward, it is necessary to conduct a recalibration every three months to guarantee the accuracy of the monitoring system over the long term.
This calibration process is entirely compatible with the low-cost Hall effect displacement sensor that you have selected for domestic production. It can be rapidly completed on-site in the injection moulding workshop and does not necessitate costly professional calibration equipment.
