A perfectly performing feeder is worth little if it can’t maintain its performance over the long haul.
Historically, many factors contributed to performance drift such as feeder type, analog control and weigh systems, the feeder’s mechanical systems, maintenance, and the operating environment itself. However, today’s more sophisticated digitally based feeders have eliminated many of these causative factors, and stable, drift-free operation is now more the norm than the exception.
Drift is detected by calibration checks, and is typically remedied by a simple weight span adjustment. In the accompanying diagram the red line represents a condition in which the feeder has drifted far out of calibration. Nowhere throughout the feeder’s operating range does the measured rate equal the set rate. By adjusting the feeder’s span setting the line is rotated so that perfect correspondence between set and measured rate can be restored throughout the feeder’s operating range, represented by the blue dashed line.
The user must ultimately determine the appropriate frequency of calibration checks based on operational experience, but the question of stability is worth considering when purchasing a new feeder. Significant and ongoing cost savings in maintenance labor, off-spec product, and potential process downtime can be realized by selecting a feeder designed for stable, drift-free operation.