Coperion Pharma InFocus


LIW versus GIW Dispensing Defined

Advantages and comparison between gain-in-weight (GIW) and loss-in-weight (LIW) batching techniques.

Gain-in-Weight (GIW) Batching Principle Using Twin Screw Feeders

In GIW batching volumetric feeders sequentially feed multiple ingredients into a collection hopper mounted on load cells. Each feeder delivers approximately 90% of the ingredient weight at high speed, slowing down towards the end of the cycle to deliver the last 10% at a reduced rate to ensure higher accuracy. The GIW controller monitors the weight of each ingredient and signals each volumetric feeder to start, increase or reduce speed, or stop accordingly. Once all the ingredients have been delivered, the batch is complete and the mixture is discharged into the process below. It should be noted that this type of batching method is sequential for each ingredient, and therefore generally results in a longer overall batching time than with LIW batching (outlined below) if the number of ingredients is high.

For further illustration of the actual GIW batch process watch the following video:

Gain-in-Weight (GIW) Batching Principle

Loss-in-Weight (LIW) Batching Using Gravimetric Feeders

If you require high accuracy for the individual ingredients, low overall batching time, or both, then LIW batching will be more efficient. In this method, gravimetric feeders operating in batch mode simultaneously feed multiple ingredients into a collection hopper. Each of the feeders is on load cells or scales, and the material lost from the feeder is weighed. Adjustment of the delivery speed (on/off, fast/slow) lies with the LIW feeder controls and the smaller weighing systems deliver highly accurate batches for each ingredient. Since all of the ingredients are being delivered simultaneously, the overall batch time is greatly reduced. Additionally, the system's highly accurate load cells specifically sized for the individual ingredient batch weights increase batch accuracy. This method is often used for more expensive micro-ingredients. However, it should be noted that this system could also be more costly, because each feeder requires individual weighing devices.

For further illustration of the actual LIW batch process watch the following video:

Loss-in-Weight (LIW) Batching Principle

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