Net weigh and gross weigh fail differently
A net-weigh filler weighs the product on its own, in a weighing vessel, and then drops it into the bag. Bag tolerance never enters the number, which is why net weigh holds accuracy across cheap bags.
A gross-weigh filler weighs bag and product together and subtracts a stored tare. It is simpler and faster, and it inherits every gram of variation in the bag itself.
Four sources, in the order they usually appear
In-flight product. The filler stops the feed when the scale reads target minus an expected free-fall. That expectation depends on product head in the silo and on how the product flows today, and a silo drawn from full to a third changes it.
Zero drift. Load cells move with temperature. A machine that starts cold and runs all day will wander unless the zero is re-captured between cycles.
Bag tare. On a gross-weigh machine, a supplier change in bag weight appears as a weight change on every bag, with no fault anywhere.
Moisture. Bulk density follows humidity, so the same volume weighs differently on a dry morning and in the rain.
Check in this order, not the other way round
Calibrate with certified weights first. If the scale is right, everything downstream is a product or settings question; if it is wrong, every other measurement you take is noise.
Then run empty cycles and watch the tare. Then fill one bag slowly — by hand if the machine allows — and watch where the weight actually lands relative to target. Only then touch the compensation.
What automatic compensation can and cannot fix
An adaptive filler can learn a systematic offset: a product that consistently overshoots by 40 g gets corrected. It cannot remove scatter. Two bags from the same batch landing 60 g apart is a feed-resolution or stability problem, not an offset problem.
If scatter is the complaint, look at the feed. A two-speed feed with a stable slow-approach rate does more for consistency than any correction factor.
Where to look next
The two-speed approach that keeps scatter down is easier to see than to describe: a twin-hopper granule bagger spends most of its cycle in the slow stage.
If the numbers still do not settle, the questions we get asked most are collected in the FAQ, and the machines themselves are under automatic bagging machines.