Improving Weigh Feeder Control Using Scale Location Compensation

This paper describes how "Scale Location Compensation" can be used to improve weigh feeder performance in various applications. Scale Location Compensation ("SLC") was developed by Thayer Scale to meet special systems needs in 1976 (1) (2) (3) (4), and is used in control loops to effectively move the point of measurement and control from the scale's physical location on the conveyor belt to some downstream point which better serves the response needs of a downstream process. FUNDAMENTAL EXAMPLES OF MEASUREMENT & CONTROL UNCERTAINTY: 1. Uncertainty of Control of Discharging flow from a variable speed weighbelt feeder. Note that heavy loading at scale calls for slower belt speed, yet light loading at head pulley requires opposite response if desired flow rate is to be achieved at the discharge. 2. Uncertainly of Measurement of Discharging flow from load-out conveyors. Note that conveyor scale is located near tail end, where belt tension is lowest, to assure best accuracy. Thus, all the material between scale and head pulley has been totalized but not delivered.