Due to their relatively low up-front costs, batch weighing systems are a common production setup in many industries. In addition to improving product quality over traditional manual batch weighing methods, automation of the material handling, product transfer, and batch weighing processes can greatly increase overall efficiency. Properly weighing and accurately delivering the ingredients without manual intervention can result in several process advantages, including overall safety, fewer mistakes, better accuracy, lower bulk material costs, improved product quality, and savings in manufacturing costs.

When considering an automated batch weighing system, it’s important to look at several factors that will influence the type of batching system recommended and optimize ingredient cost savings and overall return on investment (ROI). The main considerations include deciding between a gain-in-weight (GIW) or loss-in-weight (LIW) system, deciding between volumetric or gravimetric feeders for batch accuracy, determining your desired batch times, knowing the number of ingredients and their characteristics, and knowing the space limitations.

Gain-in-Weight Batching Principle

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:

Loss-in-Weight Batching Principle

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. It should be noted that this system could be more costly, because each feeder requires individual weighing devices, but the improved accuracy reduces ingredient costs associated with overfeeding in the long run.

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

Each of these technologies has inherent advantages and limitations. To choose the most efficient system, it’s important that you review the critical criteria required for the system as a function of batch time, accuracy required, amount of time allowed for quick changeover and cleaning, and of course, overall cost.

Optimization of batch accuracy will also be a function of the load cell resolution. For example, in GIW batch weighing, when discharging into a hopper or receiver on load cells, the accuracy is a function of the full scale load of the receiving vessel plus the material. A system designed to add both major and micro ingredients in the same vessel may not be able to accurately detect the smaller ingredient amounts. In this case using a combination of GIW and LIW batching can be advantageous; macro ingredients are fed using GIW batching and LIW batching ensures micro ingredients are added accurately.

It’s important to discuss all these options with the batching system supplier to ensure that you get the most efficient overall batch weighing operation.