Loss-In-Weight feeders have replaced volumetric feeders over the years where a higher degree of accuracy is required. Technopark Automation & Control have supplied Loss-In-Weight feeders controlling mass flow rates between grams/hour and several tons/hour.
Principle of operation
Volumetric feeders rely on the bulk density of the product being constant. A Loss-In-Weight feeder can be defined as a self learning volumetric feeder where the controller compensates for bulk density changes on a continuous basis.
The Loss-In-Weight system is based on a suitably selected weigh hopper with load cells and a feeder, be it belt, screw or a vibratory feeder. The weight loss of the weigh hopper is recorded over time by the Loss-In-Weight controller which will then make adjustments to the feeder to delivery the correct rate of flow rate.
Loss-In-Weight feeders are typically used on extruders or systems where additives are dosed on a continuous basis at low flow rates. A combination of belt weigh feeders and Loss-In-Weight feeders may be appropriate in certain instances, depending on the process design and material flow properties.
Loss-In-Weight feeders can also be used for liquids where product will be pumped into a continuous process.
Loss-In-Weight feeder sequence
A Loss-In-Weight feeder will typically go through the following sequence:
- 1. Rapid refill of the Loss-In-Weight weigh hopper. During this part of the sequence the controller will be in the volumetric mode.
- 2. Delay to stabilize the reading.
- 3. Gravimetric discharge mode until the weigh hopper low level is reached.
Every Loss-In-Weight feeder is designed to suit specific client requirements.