For unstable aseptic bag weights, separate an average offset from excessive bag variation, then investigate the product and valve action using the actual measuring principle. Verify the reference scale and empty bag weight first, and judge adjustments through repeated fills under comparable conditions.
What does bag weight deviation actually mean?
Bag weight deviation refers to the difference between actual net contents and the target. Ask two questions: is the average fill on target, and how far apart are the lightest and heaviest bags? Both can be wrong at once. A correct average alone does not mean every bag is acceptable.
Why do the two cases need different checks?
A steady offset points you towards settings and persistent measurement errors. A wide spread calls for a closer look at changing signals and valve action. Ten bags give an initial screen; use the table to narrow the investigation and collect more data where needed.
|
What you see |
Where it starts |
What to check |
What to do |
|
Every bag light or heavy, spread tight |
Tare, settings or conversion |
Tare for weighing; density for volume conversion |
Verify the relevant settings and reference measurement |
|
Average fine, bags scatter |
Repeatability of the meter |
Signal stability of the flow meter or load cell |
Check the signal, then compare valve timing |
|
Drifts lighter through the run |
Possible supply or air changes |
Tank level, feed pump, air in the line |
Set a low level limit, check the suction side |
|
Worse after a product change |
Changed product and operating conditions |
Which product the meter was sized for |
Review conditions; recalibrate if required |
|
A fixed few kilograms off on every bag |
Tare or bag format |
Tare setting against the bag actually used |
Correct the tare to the bag in use |
|
Leaks found after sealing |
Inspect packaging and fill interface |
Fitment, cap seating and seal damage |
Inspect the fitment, cap and sealing surfaces |
How does the product itself move the weight?
Thick product can keep dripping after the close command. Air can disturb flow meters, and temperature matters when a measured volume is converted into weight using density. A load cell measures mass directly, so it does not need that conversion. It still needs a stable platform and a controlled stop to the flow.
Which measuring principle fits which product?
Start by asking how the filler knows that a bag is full. Load cells weigh it, electromagnetic meters measure volume, and Coriolis meters measure mass. Their checks differ. Both 200 litre bags and 1000 litre containers can use flow meters; size alone does not decide the system.
|
Principle |
Selection conditions |
Where it drifts |
|
Electromagnetic flow meter |
Conductivity, flow range and meter size |
Gas, incomplete filling of the pipe and installation |
|
Coriolis mass meter |
Flow range and allowable pressure loss |
Gas, vibration, zero stability and installation |
|
Load cell weighing |
Rated load and required cycle |
Tare, external contact, vibration and cutoff lag |
Why check valve response as well as sensors?
A close command does not stop product instantly. Valve response and dripping after closure can change the final weight, while a sensor can drift without an alarm. Compare the signal and close command with the finished bag weight. On a twin head machine, keep separate records for each head so the average cannot hide an offset.
When is it a setting and when is it a selection problem?
Wrong tare, target or compensation can be corrected in the settings. Sensor drift, a worn valve, contact with the weighing platform or unstable supply need their own fixes. A failed calibration does not prove that the machine was selected wrongly. Check its operating limits before deciding on new equipment.
How should the figure be checked at acceptance?
Agree on the product, bag, speed and reference scale before acceptance. Weigh thirty consecutive bags, recording the average net weight error and the gap between the lightest and heaviest. For example, ±0.5% at a 200 kg target means ±1 kg. Use the tolerance agreed for the project; the example is not a general accuracy claim.
The takeaway is to classify the pattern, check the relevant measuring system, then verify the fix. Both average net weight and bag variation need to meet the agreed limits.