Scale Calibration - Weights, Tolerances, and Frequency?
Hello all, I'm writing our Scale calibration SOP/Program and I cant find any concrete information on calibrations. Right now based on finding stuff online about Scale tolerances I have this in my draft SOP: Weight Range, Tolerance, Less than 1 pound, ± 0.1 grams, 1.0-11.0 pounds, ± 1 grams, 11.01-150.00 pounds, ± 10 grams. Also I'm looking for help on what I actually need for calibration weights. As of right now we do zero calibration. I'm setting up a yearly calibration for a 3rd party very soon. But for now I'm looking to purchase some calibration weights for our scales for the daily/weekly/monthly verification? Right now we use scales for our finished product packaging (2oz up to 12oz pouches) that max out at 11 pounds. I'm thinking of purchasing a 50g and a 500 gram weight to verify those scales. We also have ingredient Scales that go up to 150 pounds max. Normally we don't weigh anything over 50 pounds. So I was thinking of buying a 10LB weight and a 50LB weight to verify these scales. My questions are as follows:
Are there actual guidelines on what I should use for tolerances? I've found some info on scale intervals and resolutions but I must be a little dense because I cant follow it and make any sense of it. Not that it matters though because these scales are so old the labels are either missing or unreadable.
Are these possible acceptable weight calibrations? My old job we did lowest and largest weight normally weighed. I was thinking 50 pounds but the new production manager said a 10LB weight should be more then acceptable.
Do the calibration weights need to be NIST Traceable($ factor)?
How frequently do we need to verify the scales once this process gets going? My old job we did it daily and the production manager here is saying they did it monthly at his old place. We're both new here as this business has just started to grow out of the MA & POP stage and trying to get SQF certified. We're a RTE granola product if that matters. Thanks in advance for any help at all!
Before I add my 2 cents
What are you using your scales for? are any of them for weighing Finished Goods?
Before I add my 2 cents
What are you using your scales for? are any of them for weighing Finished Goods?
The smaller scales will be for weighing the pouches of finished product. right now we have 2 ounces to 12 ounce pouches. The packaging machine weighs it out we're just going to use the smaller scales to make sure the weights are reaching the minimum weight that is labeled on the pouch.
The bigger scales are for ingredient weighing for the mixing batches. Also we have one in shipping that weighs the case pack totals.
You should be able to find what you need in the attached link
https://www.nist.gov...17-webfinal.pdf
I wouldn't spend the money on the NSIT weights for verifications--they are REALLY expensive and once dropped are useless (and they will get dropped)
I've never done lowest and highest weights, but would suggest you consider having your largest scale adjusted down, the bigger the highest weight allowed, the less accuracy you get. Generally, a good company should be able to switch out circuit boards for cheap and recertify the scale
I would perform daily verification on the scale used for units of FP and monthly on all scales used for inhouse batching only
You're ranges look good to me
Are there actual guidelines on what I should use for tolerances?
There's a rule of thumb. The tolerance must be (at least) smaller than the 1/10 of measured value. Ex. for 10lbs, tolerance <= ±1lb
Are these possible acceptable weight calibrations?
A scale is only reliable within its calibrated range. For example, the max & min calibration weights are 50lbs & 10lbs, such a scale cannot be used to weight things heavier than 50lbs and lighter than 10lbs.
Do the calibration weights need to be NIST Traceable($ factor)?
Yes, but possibly by an indirect link. You can have an accredited institute certify them, no need to ask NIST.
How frequently do we need to verify the scales once this process gets going?
The interpretation of this remains so complicated. Annually or semi-annually are most common frequencies. Some may disagree and argue for shorter intervals. Any frequencies that satisfy auditors or customers or management's experiences are right frequencies.