An instrument for monitoring and controlling flow by means of loss of weight from a vessel.
The vessel contents are maintained by a service hopper allowing continuous flow to be maintained. The analogue output from the instrument controls the speed of a screw conveyor, and thus the flow rate of the product.
With hopper weight as signal input, constant weight of product per unit time is maintained using a PID loop. When the hopper level drops below a preset amount the averaged power level for the last eight cycles is sent to the screw conveyor while the hopper is automatically refilled. Once refilled, the averaged power level is held for five cycles before restoring PID control.