Loss-in-Weigh Feeders are based on continuous weight loss measurement with respect to time principle. Weigh hopper with a screw feeder is installed on three load cells of suitable capacity, which in turn connected to Load transmitter to convert it into 4-20mA output for Weigh feeder controller. In a second 30-40 weighments are done for bulk material in the weigh hopper and loss of weight with respect time (i.e. feed rate) is calculated. It generates output for controlling the speed of the screw feeder to get desired TPH.
The hopper is slowly emptied (normally 3 to 30 minutes between refills) at constant feed rate. While refilling, the last TPH is recorded, speed is kept constant and refilling is done in short interval. Material during refilling is assumed to be fed at constant feed rate (i.e. volumetric feeding) and totalizer is updated to get the best accuracy at continuous feeding.