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What Is a Loss in Weight Feeder?
A Loss in weight feeder is a gravimetric feeding system that measures material flow by tracking the loss of hopper weight over time. Unlike volumetric feeders, it does not rely only on screw speed or material volume. Load cells continuously monitor the hopper, while a control system adjusts the feeder speed to maintain the target rate. This makes the equipment valuable in plastics, food processing, chemicals, pharmaceuticals, and other industries requiring consistent dosing.
The operating principle is simple, but real conditions are not. As material leaves the hopper, the measured weight decreases. The controller compares this change with the required feed rate and corrects the motor speed. During refilling, the system usually switches between gravimetric and volumetric control. A steady refill process matters. Sudden vibration, bridging, moisture changes, or poor calibration can distort the reading and create unstable output.
Small details matter.
In practical installations, technicians should inspect load-cell mounting, flexible connections, screw condition, and refill timing. Experience shows that a feeder may perform well during testing but drift after several hours of production. That difference deserves attention, not excuses. Calibration procedures should follow the manufacturer’s instructions and be verified with actual material. Operators should also record feed-rate trends instead of trusting one successful reading. A Loss in weight feeder is precise equipment, yet it is not self-correcting. Proper setup, routine observation, and documented maintenance support reliable performance. Some applications still require additional testing, because material behavior can be surprisingly inconsistent.
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Definition and Basic Function of a Loss-in-Weight Feeder
What Is a Loss in Weight Feeder?
Definition and Basic Function of a Loss-in-Weight Feeder
A loss-in-weight feeder is a gravimetric device that measures material flow by tracking weight reduction over time. It usually contains a hopper, load cells, a controller, and a controlled discharge mechanism. The mechanism may be a screw, belt, or rotary valve.
The operating idea is direct. Material leaves the hopper, and the measured weight decreases. The controller calculates the loss rate and adjusts the discharge speed to maintain the target feed rate. It does not simply measure volume. That matters when bulk density changes during production.
Small details affect performance. Vibration can disturb the load-cell signal. Humidity may cause powders to stick together. Poor flow can create bridging above the outlet. These problems may produce an unstable reading, even when the drive system runs correctly.
During refilling, the hopper gains weight and normal measurement is briefly interrupted. The controller must manage this transition carefully, often using a temporary volumetric setting. After refilling, the system returns to gravimetric control. In practice, this boundary is not always perfectly smooth.
Reliable operation depends on calibration, stable mounting, correct material testing, and regular inspection of weight trends. Operators should check whether the actual feed rate matches the process demand, rather than trusting one display value. No setup stays perfect forever. A feeder can work well today and drift tomorrow, especially when material properties change.
What Is a Loss in Weight Feeder? - Definition and Basic Function of a Loss-in-Weight Feeder
| Category | Parameter or Concept | Definition or Typical Data | Basic Function and Practical Note |
|---|---|---|---|
| Definition | Loss-in-weight feeder | A gravimetric feeding system that determines material flow from the measured reduction in hopper weight over time. | It measures the actual mass being discharged rather than relying only on screw speed or volumetric displacement. |
| Measurement Principle | Weight loss rate | Mass flow rate = decrease in material mass ÷ elapsed time | For example, a 2 kg decrease over 60 seconds corresponds to an average flow rate of 2 kg/min. |
| Operating Modes | Gravimetric mode | The controller continuously compares the measured mass flow with the target setpoint. | Feeder speed is automatically adjusted to correct deviations in actual output. |
| Operating Modes | Volumetric mode | The feeder operates at a preset speed or volume-based rate without continuously calculating mass loss. | This mode can be useful during refill or when weighing is temporarily interrupted, but accuracy depends more strongly on material bulk density. |
| Main Components | Weighing hopper and load cells | The hopper, feeder, and material inventory are supported by one or more load cells that detect weight changes. | The weighing system must be mechanically isolated from rigid connections, vibration, and external forces. |
| Main Components | Feeding device | Common devices include screw feeders, vibratory feeders, belt feeders, and liquid pumps. | The selected device should match particle size, flowability, abrasiveness, moisture, and required feed rate. |
| Main Components | Controller and drive | A control system receives the weight signal and adjusts motor speed through a variable-speed drive. | The feedback loop helps maintain the commanded mass flow when material properties or hopper level change. |
| Typical Capacity | Feed-rate range | Depending on feeder design, applications may range from a few grams per hour to several tonnes per hour. | The usable range is determined by the feeder size, screw or belt geometry, material density, and required control accuracy. |
| Accuracy | Gravimetric control performance | Well-installed systems commonly target a controlled feed-rate accuracy of approximately ±0.5% to ±1.0% of the setpoint, depending on application and material. | Actual performance depends on calibration, weighing resolution, refill effects, vibration, material consistency, and feeder design. |
| Hopper Refill | Refill transition | During refill, the measured hopper weight increases, so the system may temporarily suspend direct loss-in-weight measurement. | A refill algorithm or volumetric backup mode is used to maintain a stable output until normal weight-loss measurement resumes. |
| Calibration | Weight and rate calibration | Calibration establishes the relationship between the load-cell signal, feeder speed, and actual material output. | Calibration should be repeated after maintenance, material changes, load-cell replacement, or significant process modifications. |
| Advantages | Process control benefits | Improved dosing consistency, automatic compensation for bulk-density changes, and direct mass-flow measurement. | These benefits are important in blending, compounding, extrusion, batching, chemical processing, and food production. |
| Limitations | Potential error sources | Vibration, air currents, material bridging, pulsation, buildup, unstable discharge, and mechanical interference can affect the weight signal. | Correct installation, suitable hopper geometry, grounding, shielding, and regular inspection are essential for reliable operation. |
| Typical Applications | Industrial uses | Continuous dosing of powders, granules, pellets, flakes, fibers, and selected liquids. | The feeder is commonly integrated with mixers, extruders, reactors, packaging lines, and other continuous processes. |
| Key Difference | Loss-in-weight versus volumetric feeding | Loss-in-weight feeding measures mass directly; volumetric feeding estimates mass from volume and assumed bulk density. | Loss-in-weight systems generally provide better compensation for changes in bulk density, provided the weighing signal remains stable. |