Calibration of Scales for Weigh Counting

Jen Kirley

Quality and Auditing Expert
Staff member
Admin
#11
Definitely need some "competancy adjustment" around here!
You got that right!! :agree1: A discount retailer in my area sells some bulk hardware by the pound. If their scale is not accurate, My $5.95 would perhaps buy fewer nails. Or, put another way: If my scale was not accurate, my customer would get too many parts for the price! Maybe your people would comprehend the subject if it was presented that way.
 
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R

red53angel

#12
As the parts are small and inexpensive, they always throw in a few extra, so overcount is not an issue. We have had only 1 customer say they were shorted according to their weigh count, but most customers probably do not count how many they receive since the price per piece is low.

Mary
 

WCHorn

Rubber, Too Glamorous?
Trusted Information Resource
#13
As always, great advice offered from the group!:applause:

As an additional resource, I am attaching a MS Excel worksheet which will tell you if your scale is capable of measuring the parts you are attempting to measure. When dealing with small parts (light), one must use an appropriate size scale. Many times small parts weigh less than the scales error which results in inaccurate counts.
I have found that the two biggest causes for weigh counting errors of light parts are operator miscounts of the sample and air movement. Training operators to count in groups of five has been effective for us. Putting a draft shield around the scale helps to block air drafts. This is really important when the scale is located in near a fan or open window or ventilator.
 

Helmut Jilling

Auditor / Consultant
#14
As the parts are small and inexpensive, they always throw in a few extra, so overcount is not an issue. We have had only 1 customer say they were shorted according to their weigh count, but most customers probably do not count how many they receive since the price per piece is low.

Mary
Perhaps true. But, if you put an extra three pieces in a bag of 100, that is like giving a 3% price reduction.
 

rmf180

Involved In Discussions
#15
Perhaps true. But, if you put an extra three pieces in a bag of 100, that is like giving a 3% price reduction.
Not only that, but consider id and traceability. If you are in a regulated industry and you receive a cert for 100 pieces, you cannot produce more than 100 finished items. If lot trace ends up showing that I produced 103 units, three of them cannot be certified. Which ones? :confused:
 

QChas

Involved - Posts
#16
Been doing this for over 5 years at 2 different companies and using 2 different registrars ........

1) Get a set of weights and have them calibrated by an outside lab with a cycle of 10 years. The only way the weights will need to be recalibrated before that is if someone drops them.

2) Calibrate your scales weekly using the calibrated weights and record your results. If you find a problem send the scale out for service.

This resulted in a huge savings since we used an outside service to calibrate scales monthly. As I said above, this method has been blessed by 2 different registrars. Good Luck!
 
D

Daniel Walker - 2011

#17
Been doing this for over 5 years at 2 different companies and using 2 different registrars ........

1) Get a set of weights and have them calibrated by an outside lab with a cycle of 10 years. The only way the weights will need to be recalibrated before that is if someone drops them.

I have a hard time believing that a calibration cycle of 10 years will pass for test weights. Weights can drift for many different reasons. Handling and environment are the two biggest contributors. If you have a 20 year history and can prove this, then I may change my tune. What happens if you send your weights out at the end of 10 years and they fail? Are you going to recall 10 years worth of product because your scales haven't been accurate the whole time?
 
R

red53angel

#18
I have opened a real can of worms here. We did 3 samplings of weighing 50 parts and then running it up to 1000. We found that we were only off by 1 in all 3 cases, which is acceptable. We are counting resistors and always throw a few extras into the box.
However - we sometimes fill orders from stock, possibly combining 2 or three previous boxes to complete an order. The sample came from one box and then the order was filled from 2 or three boxes. From lot to lot, there is a weight difference (up to 5%) due to manufacturing variables, such as thickness of powder coat. The manual count showed we cannot rely on this count. Presently, lots are sometimes combined prior to weigh count in the excess stock area. :frust:
So for now, the reliability of the scales seems good, but our practice of combining lots is skewing our results. Having certified weights and newly calibrated scales won't fix this one.

Thanks again to everyone for all the helpful information.
Mary
 
B

Bob Bonville

#20
Red, in this case, calibration of scales is a wise business decision. Where counts are important and relevant to a particular process, be it filling shop orders, verifying counts at R/I, or at shipping, count is important.

As one of the contributors added to the thread, periodic checks of a scales accuracy can be done by using a known standard or set of standards depending on the amount of items being measured.

As an internl QMS auditor years ago, our team was called on to perform the annual inventory accuracy verification audit. We always used calibrated scales.

Bob
 
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