7 replies to this topic

[amb]

Hi, I'm new here and I would like to have some guidance about the Net Weight Statement and the usage of Tare weights in our daily process. What would be an ideal net weight statement and the inclusion of tare weigth in the process including frecuencies and targets.

[cosmo]

Hi, I'm new here and I would like to have some guidance about the Net Weight Statement and the usage of Tare weights in our daily process. What would be an ideal net weight statement and the inclusion of tare weigth in the process including frecuencies and targets.

Hi amb,
I'm not exactly sure of what you are asking so I hope this helps.
With any product the net weight is the declared weight on the package. (Not sure about the USA, but in Australia if it is on the shelf below declared (net) weight it is a breach of the trade practices act).
In the process check weighers are set up to include tare weight (product weight plus packaging) with regular checks recorded on QA sheets. The frequency of weight checking and recording calibration checks are something for you to determine dependant on the consistency of your process weights. Remembering if you have underweight product as finished product, the amount of product withdrawn/held/reworked will be determined by the last correct weight calibration check. (the more frequent the check the smaller the volume withdrawn).
My preference for ensuring declared (net) weight is achieved is the addition of approx 4 grams (target weight) of product above declared (this depends on your product and possible moisture loss over shelf life) and is measured and recorded hourly at a minimum. Check weigher calibration checks are done 2 hourly in our plant.
Cosmo

[Cathy]

If you are looking for information on tolerances in variability of weights - try NIST Handbook 133. This is a portion of it....  MAV for Net Weight.pdf   498.82KB   123 downloads

[amb]

Thank you Cosmo,
Well your information is very helpful. We had an audit some time ago and we had a minor issue in this matter. Even though we had check lists of weight with hourly frequency and records of calibration as well. The auditor's opinion was that our process for net weight was not clear enough. He based his report in the fact that we rely in the automatic machine calibaration for our target weight and then we compare it at the end of the packaging line with tare weights. To this point, I still do not understand what we did wrong. I just want to be ready for our next audit.
Thanks,
AMB

[amb]

Nice information Cathy,
Thank you
AMB

[GMO]

I'm a bit unclear as to what the non conformance was and I have to admit to not knowing US legislation on weight control but with tare weights in the UK to treat the packaging tare as a constant, you need to establish it does not vary by more than a permitted amount (the "tare variability check") from memory I think you need to weigh 20 packages and I think it's something like the standard deviation needs to be less than one tenth of the TNE (probably meaningless for US legislation though) but I would think some measure to prove that your tare weight is constant is needed.

In addition, I would say it's good practice to check the dynamic calibration of a checkweigher at least daily using calibrated weights (you can get weights made up and calibrated to match the approximate size / density of your product normally.) Note that static weight checks are largely meaningless for checkweighers as they weigh dynamically but are also useful to do once a week or so (just because the auditors like it ). I would not rely on a yearly / 6 monthly calibration of the checkweigher as vibrations etc can cause significant drift in dynamic values.

[amb]

GMO,

Completely agree, we do that in here. In our pre operational procedures we calibrate the Scale daily with standard approved weights and then we use the tare weights according to what we are producing in that particular day.

We still think that the auditor did not have grounds for giving us the minor in the audit!

Thanks fo the imput.
AMB

[GMO]

Can you post the exact wording of the non conformance?