Technical article
How Multihead Weighers Work
A multihead weigher does not weigh one portion — it weighs many small ones at once and chooses which to combine. That idea is why it became the standard doser for irregular food products, and why its configuration matters so much.
The Path of the Product
Product enters at the top and falls through the weigher in stages:
- Top cone: a vibrating dispersion cone spreads product outwards
- Radial feeders: vibrating pans carry product to each head
- Pool hoppers: hold the next portion ready above each weigh hopper
- Weigh hoppers: each sits on its own load cell and holds a partial weight
- Collating chute and timing hopper: gather the chosen portions and release them to the packer
The Combination
At each cycle the controller knows the weight in every loaded weigh hopper. It evaluates combinations of hoppers and picks the one whose total is closest to the target without going under it. Only those hoppers open; they are refilled from the pool hoppers while the next combination is chosen.
Because the partial weights are random, there are many combinations to choose from — which is how the weigher reaches the target accurately even when individual pieces vary a lot.
Why It Suits Irregular Food
A single hopper filled to a target has to cut off the flow at the right moment, which is slow and imprecise with pieces of different sizes. Combination weighing avoids the cut-off entirely. That is why frozen vegetables, nuts, dried fruit, snacks and fresh-cut produce are typically weighed this way.
What Changes With the Product
Sticky products such as dried figs or raisins need dimpled or scraper contact surfaces, or screw feeders instead of vibratory pans. Fragile products need reduced drop heights. Frozen products need a weigher built for cold, wet conditions. The number of heads, the hopper volume and the feeder amplitude are all set by the product and the target weight.
Give-Away
Give-away is product above the declared pack weight. Over a year it adds up to a significant amount of free product, so a weigher is chosen as much for the give-away it achieves on the real product as for its speed. Both are confirmed on the product rather than quoted in general.
Working With the Packer
The weigher and the packer run as one system: the packer signals when it is ready, the timing hopper releases the portion, and a checkweigher downstream can feed back to the weigher. Most often the packer is a vertical form fill seal machine directly below; pouch machines and tray lines are also common.
Next step
Evaluate the process on your product.
The correct automation decision depends on your product, line layout and target process.