A loss-in-weight feeder mounts a screw or twin screw metering unit and its hopper on precision load cells and controls screw speed to hold the measured rate of weight loss exactly at setpoint. It converts volumetric metering into true mass flow control with 0.25 to 0.5 percent accuracy, the standard for recipe-critical continuous dosing from 0.1 to 300 kg/h.
The controller differentiates the weighed system mass over time to obtain the actual mass flow and trims screw speed continuously against the setpoint, cancelling density and fill-level effects. When the hopper reaches its low level, a refill valve recharges it in seconds while the controller freezes gravimetric action and drives the screw at the learned volumetric speed, returning to weight control once refill settles.
Challenges
Weight Signal Corruption by Plant Vibration
Floor and machine vibration superimposes noise on the load cell signal, degrading rate resolution at micro feed rates.
Accuracy Loss During Refill
During hopper refill the weight signal rises, blinding the gravimetric loop exactly when feed must continue.
Pipe and Sleeve Forces on the Weighed Mass
Rigid connections to refill and discharge lines shunt force around the load cells, biasing the measurement.
Pressure Transients from Downstream Equipment
Suction or pressure pulses from receiving mixers and conveyors act on the weighed hopper as false weight changes.
Calibration and Verification Burden
Regulated processes demand documented proof that the indicated rate equals true mass flow over time.
Solutions
- Vibration-Isolated Frame with Digital Filtering: Isolation mounts beneath the scale frame plus adaptive digital filtering in the controller recover clean rate resolution on production floors.
- Learned Volumetric Bridging Through Refill: The controller stores the current mass-per-revolution and runs volumetric during refill, holding rate within specification until weighing resumes.
- Flexible Sleeves and Force-Free Piping: Long flexible sleeves at inlet and outlet, with piping supported independently, keep external forces off the weighed system.
- Pressure Compensation and Vent Balancing: Vent lines balancing hopper headspace to the receiving vessel, with pressure compensation in the controller, cancel transient false-weight effects.
- Integrated Catch-Weight Verification Port: A diverter and catch container at the discharge allow timed verification runs, documented automatically against the indicated totaliser.
Applications
- Continuous Pharma Manufacturing Lines: Ratio-controlled feeding of API and excipients into continuous granulation and direct compression (ICH Q13).
- Extrusion Compounding Additive Feed: Precise additive and filler dosing into twin screw compounding extruders.
- Infant Formula Recipe Dosing: Gravimetric micro dosing of vitamins and minerals into base powder streams.
- Detergent Enzyme and Perfume Carrier Dosing: Accurate minor component addition into post-tower blending.
- Continuous Food Mixing Lines: Holding recipe ratios of minor ingredients on continuous snack and beverage powder lines.
Model Range and Capacity: JBM-MF-W Series
Basis: Accuracy as 2-sigma deviation over 1-minute samples at mid-range, SS 316L contact parts.
| Model | Metering Screw | Feed Rate (kg/h) | Accuracy (2-sigma) | Hopper (L) | Refill | Contact Material |
|---|---|---|---|---|---|---|
| JBM-MF-W05 | Single 12 mm | 0.1 – 2.4 | 0.5 % | 5 | Pneumatic valve | SS 316L |
| JBM-MF-W15 | Single 20 mm | 0.3 – 15 | 0.5 % | 10 | Pneumatic valve | SS 316L |
| JBM-MF-W50 | Twin 30 mm | 1 – 36 | 0.25 % | 25 | Vacuum refill | SS 316L |
| JBM-MF-W150 | Twin 40 mm | 2.5 – 90 | 0.25 % | 50 | Vacuum refill | SS 316L |
| JBM-MF-W300 | Twin 50 mm | 5 – 180 | 0.25 % | 75 | Vacuum refill | SS 316L |