Gravimetric Feeder
Why choose gravimetric instead of volumetric feeding?
Choose gravimetric when bulk density varies, when the process requires tight mass accuracy, or when logged consumption data is needed for quality or regulatory control. Gravimetric feeders measure actual weight loss, making them self-calibrating and resilient to moisture, particle size, and flow changes.
What is the control variable in a loss-in-weight feeder?
The control variable is the rate of weight decrease over time, expressed as mass flow. The controller maintains this by changing feeder speed, typically through PID-style closed-loop control, using load cell readings compared against the setpoint.
What hardware is typically present in a gravimetric feeder?
A hopper, weigh frame or load cells, a feed mechanism such as a screw or belt, a speed feedback device such as a tachometer or encoder, and a digital controller/PLC. This combination provides closed-loop mass flow control and data logging.
A gravimetric feeder is a mass-based dosing system that controls material delivery by weight per unit time instead of volume, using load cells, a controller, and a feed device. In loss-in-weight configurations, the hopper sits on weighing elements; as material discharges, the controller measures weight loss and adjusts feeder speed to maintain setpoint. This self-calibrating approach handles changing bulk density, moisture, particle size, and flow behavior.
In plastics, food, chemical, and pharmaceutical production, gravimetric feeders meter resins, powders, pellets, colorants, additives, and other bulk solids into mixers, extruders, compounding lines, or batch vessels at a controlled mass rate. On the shop floor, an operator enters a recipe setpoint such as kg/h or a batch weight target; the controller reads hopper weight, computes actual mass flow, and trims screw or belt speed to keep output stable when material density or flowability changes. The same weight-based principle supports raw material tracking through recorded usage data for recipe compliance, consumption logging, and loss analysis, because actual drawn material is measured rather than estimated from motor speed. In warehousing or receiving-linked material handling, this enables precise issuance from bulk containers, especially where batch accuracy matters more than fill volume. The advantage is tighter recipe control, lower overfeed risk, and support for high-value materials, tight tolerances, and regulated documentation.
Bridging or rat-holing in the hopper: Fine powders, hygroscopic materials, or irregular pellets can arch over the outlet, starving the feeder even while the controller demands the correct rate. The system may look calibrated while actual flow remains intermittent.
Vibration or mechanical interference with load cells: External vibration from conveyors or poor mounting corrupts the weight signal, producing unstable feedback and speed hunting. Short-term overfeed/underfeed oscillation follows, ruining recipe consistency.
Incorrect assumptions about material state or refill timing: Refill cycles or low heel levels make the feeder rely on estimation instead of true loss-in-weight. Bad refill logic or tuning causes batch drift, missed setpoints, and process surges.