How to calculate the minimum Value of Mass needed for Scales Calibration?

F

FIRAS_N

#1
Hello for all members ,,,

i would like to ask about Scales Calibration ,,, what is the minimum value of Mass ( weight ) needed to calibrate the scale?

for Example if i have Electronic Scale with Max. Capacity of 750 Kg with d=100 g
what is the Range of Weights / Mass that we need to make Calibration for4 this weight?

i need to use weight till 200 Kg, 250 Kg, 300 Kg, .... please if there are some Equations or Rules to Calculate that provide me ,,, with My Best Wishes for all.
 
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C

Chance

#2
Hello for all members ,,,

i would like to ask about Scales Calibration ,,, what is the minimum value of Mass ( weight ) needed to calibrate the scale?

for Example if i have Electronic Scale with Max. Capacity of 750 Kg with d=100 g
what is the Range of Weights / Mass that we need to make Calibration for4 this weight?

i need to use weight till 200 Kg, 250 Kg, 300 Kg, .... please if there are some Equations or Rules to Calculate that provide me ,,, with My Best Wishes for all.
Hi, please refer to the user's manual of your scale. It will tell you how to calibrate your scale.
In my case, some of our scales don't have user's manual anymore, so we did a research in internet and created internal procedure. To calibrate a scale in compliance to ISO 9001 (we are), we purchased test weights along with statement of accuracy traceable to national standards like NIST.
We then use at least three mass weights, one close to the minimum capacity, one close to middle capacity and one close to maximum capacity of the scale. We also set tolerance.
 

Jerry Eldred

Forum Moderator
Super Moderator
#3
NIST Handbook 44 "SPECIFICATIONS, TOLERANCES, AND OTHER TECHNICAL
REQUIREMENTS FOR WEIGHING AND MEASURING DEVICES" contains detailed standard tolerances, methods, etc. for calibrating scales. Depending on your quality system, you may or may not use it, but it is a very good resource.
 
F

FIRAS_N

#4
Hi, please refer to the user's manual of your scale. It will tell you how to calibrate your scale.
In my case, some of our scales don't have user's manual anymore, so we did a research in internet and created internal procedure. To calibrate a scale in compliance to ISO 9001 (we are), we purchased test weights along with statement of accuracy traceable to national standards like NIST.
We then use at least three mass weights, one close to the minimum capacity, one close to middle capacity and one close to maximum capacity of the scale. We also set tolerance.
thank you Chance, i used weights in range similar to the range of the scale, so when i make scale with Max. 750 kg i used weights until 750 Kg, but may be we need to fix weights until the middle range in the Calibration Records so we are also ISO 9001 certified, and the external auditor advice me to use NIST or OIML Standard to find Table or Equation to find the relation.
 
F

FIRAS_N

#5
NIST Handbook 44 "SPECIFICATIONS, TOLERANCES, AND OTHER TECHNICAL
REQUIREMENTS FOR WEIGHING AND MEASURING DEVICES" contains detailed standard tolerances, methods, etc. for calibrating scales. Depending on your quality system, you may or may not use it, but it is a very good resource.
thank you Jerry Eldred, i will review and read the NIST Handbook 44 off course it is useful,
 

BradM

Staff member
Admin
#6
Jerry is very correct about Handbook 44. Do be on notice, though, it is a pretty extensive document. :D Handbook 44 is written primarily for vendors calibrating large scales (like truck scales). For large scales, the standard allows for abbreviated range testing; meaning it is acceptable to check a scale up to 50% of range. That may not always serve the needs in the best manner.

I think you should be evaluating how you use the scale/balance also. I'm not as sure about scales (typically using 3-4 load cells), but analytical balances (typically with 1 sensor) has a "sweet spot". So if you have a balance with a range of 0-1000 grams, it's optimal operating area is around 50% (500 grams). It will become much less stable as you get closer to 0%, with trying to weigh 10 grams will be challenging (if you are verifying repeatability). If an analytical balance is used for assay measurement in the FDA realm, per USP 41 the minimum weight must be identified and documented. Not a bad idea to do on any balance, though.

So you should consider qualifying your scale. What is the range of the scale, and what test points do you use it at? Consider what the maximum weight that will be applied to the scale, and the minimum (probably if you tare out a container or something).

Typically, we try to hit around 10%, 50, and 90% of full range (if applicable). Otherwise, you should shoot for something like 0, 25, 50, 75, and 100% of use range. Don't forget to conduct corner load tests.

Mass Standards:

In general, try to purchase several small denomination weights. There is a pretty big difference in moving around 10, 5kg weights and one 50kg weight.:) There's a huge difference between 1 500 kg weight and 10 50 kg weights; and so on. You can construct metal carts to transport the weights. If you can stay small, around 20 kg and below per weight, someone should easily be able to lift them. From there up, you will probably want a hoist/pulley system.

Depending on the desired accuracy, Class F weights should be good.

Unless you have a lot of scales, it may not be worth it to do it yourself. There may be a local competent lab to do it for you. However, do recall they may not check it up to full range (per Handbook 44).
 
F

FIRAS_N

#7
Jerry is very correct about Handbook 44. Do be on notice, though, it is a pretty extensive document. :D Handbook 44 is written primarily for vendors calibrating large scales (like truck scales). For large scales, the standard allows for abbreviated range testing; meaning it is acceptable to check a scale up to 50% of range. That may not always serve the needs in the best manner.

I think you should be evaluating how you use the scale/balance also. I'm not as sure about scales (typically using 3-4 load cells), but analytical balances (typically with 1 sensor) has a "sweet spot". So if you have a balance with a range of 0-1000 grams, it's optimal operating area is around 50% (500 grams). It will become much less stable as you get closer to 0%, with trying to weigh 10 grams will be challenging (if you are verifying repeatability). If an analytical balance is used for assay measurement in the FDA realm, per USP 41 the minimum weight must be identified and documented. Not a bad idea to do on any balance, though.

So you should consider qualifying your scale. What is the range of the scale, and what test points do you use it at? Consider what the maximum weight that will be applied to the scale, and the minimum (probably if you tare out a container or something).

Typically, we try to hit around 10%, 50, and 90% of full range (if applicable). Otherwise, you should shoot for something like 0, 25, 50, 75, and 100% of use range. Don't forget to conduct corner load tests.

Mass Standards:

In general, try to purchase several small denomination weights. There is a pretty big difference in moving around 10, 5kg weights and one 50kg weight.:) There's a huge difference between 1 500 kg weight and 10 50 kg weights; and so on. You can construct metal carts to transport the weights. If you can stay small, around 20 kg and below per weight, someone should easily be able to lift them. From there up, you will probably want a hoist/pulley system.

Depending on the desired accuracy, Class F weights should be good.

Unless you have a lot of scales, it may not be worth it to do it yourself. There may be a local competent lab to do it for you. However, do recall they may not check it up to full range (per Handbook 44).
thank you very much BradM for your clarifications, really Handbook 44 is very useful and i found all information that i need for the minimum weights needed for calibration,
i found the table - minimum test weights and test load page 2-31 from handbook 44,
thank you for all members share us here.
 
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