Does Automatic Compensation Technology Require Regular Calibration?

Due to its advantages of automation and lightweight construction, automatic compensation technology, a popular technique for correcting hot runner sensor anomalies, has become normal practice in the daily maintenance of small and medium-sized injection molding facilities. But many practitioners question if routine human calibration is still required if automatic compensation is already enabled. Indeed, automatic compensation cannot take the role of routine manual calibration. To guaranty long-term accuracy, even sophisticated technology needs to be paired with fixed-cycle manual calibration.

We must first define automatic compensation for hot runner sensors in order to comprehend this problem. At the moment, the majority of automated compensation systems on popular injection molding machines are "daily automatic zero-point compensation upon startup." The basic idea is that the system automatically depressurizes after the machine reaches the working temperature, gathers the sensor output in the present zero-pressure state, and then performs software calculations to adjust the current output offset to the standard zero point. As part of "daily correction of small deviations," it essentially only corrects the slight, gradual drift brought on by the previous day's production; it is unable to address the underlying issue.

On the one hand, sensitivity deviation cannot be corrected by automatic compensation; only zero-point drift can. Aging diminishes sensitivity, or the difference between the sensor's output change and its original value under the same pressure, in addition to causing zero-point drift. This deviation is a physical alteration brought on by component aging and diaphragm corrosion. Changes in sensitivity cannot be detected or corrected by automatic compensation; it just modifies the zero point. For instance, a Kistler 6125A sensor's sensitivity has dropped by 8% after three years of usage. The output variation at full-scale pressure persists despite automatic compensation's ability to fix the zero point to 4mA, which results in process errors. Batch problems may result if this issue is not identified by routine manual calibration.

However, errors are accumulated by automated compensation. Every day, automatic compensation adjusts according to the variation from the day before.

Even minor mistakes add up over time. After a month, even a daily error of 0.01 mA will add up to 0.3 mA, or a 0.5% FS variation, which satisfies the requirement for significant drift. Only human disassembly and calibration, when compared to factory characteristics, can show that the variation has surpassed the norm; automatic compensation is unable to identify this accumulated inaccuracy. Sensors age more quickly and develop errors more quickly, especially when processing corrosive raw materials such glass fiber reinforced plastics, PEEK, and fluoroplastics. This calls for prompt human calibration.

After turning on automatic compensation, how frequently should manual calibration be carried out? This cycle depends on how old the sensor is. For new or lightly aged sensors that have recently undergone deep cleaning, automatic compensation can effectively offset minor daily drift, and manual calibration can be set every 1-2 months; for moderately aged sensors that have been used for more than 2 years, where sensitivity has already slightly decreased, it is advised to shorten the manual calibration to every 2-4 weeks to promptly detect deviations exceeding the compensation range; for scenarios with severe drift, where automatic compensation is used to temporarily maintain production until new sensors arrive, manual calibration must be done every week and the zero point must be retested before work each day to prevent abrupt deviations from having an impact.