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Check Weights against Accredited Weights

scales weight sop

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#1 MusselsGalore

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Posted 04 October 2018 - 09:19 PM

We have a dozen or so portable bench scales that we deploy out on boats for shellfish harvest and bagging.

 

We have accredited weights on hand.  Our procedure right now is to check the accuracy of the scale against the accredited weight.  

 

We also have a bunch of accredited weights with expired certificates.

 

Does anyone have a SOP for using a single accredited weight to verify the "check weights" used to verify the accuracy of the bench scales?

 

The scales and weights are used in a saltwater wet operation, so keeping the precious accredited weight dry and free from corrosion is difficult.

 

I would like to keep one accredited weight on hand in a controlled environment and verify check weights against the accredited weight, then use the verified check weights to check the accuracy of the bench scales.

 

Any tips?



#2 Charles.C

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Posted 04 October 2018 - 10:07 PM

We have a dozen or so portable bench scales that we deploy out on boats for shellfish harvest and bagging.

 

We have accredited weights on hand.  Our procedure right now is to check the accuracy of the scale against the accredited weight.  

 

We also have a bunch of accredited weights with expired certificates.

 

Does anyone have a SOP for using a single accredited weight to verify the "check weights" used to verify the accuracy of the bench scales?

 

The scales and weights are used in a saltwater wet operation, so keeping the precious accredited weight dry and free from corrosion is difficult.

 

I would like to keep one accredited weight on hand in a controlled environment and verify check weights against the accredited weight, then use the verified check weights to check the accuracy of the bench scales.

 

Any tips?

 

Hi MG,

 

"Accredited" should probably be "Certified".

 

To answer yr query, need to know a little more,eg  -

 

(1) what specific certified weights do you have ? These are "masters"

 

(2) what specific other checkweights do you wish to "calibrate" (assumed to an accuracy offered by the certified items).These will be "sub-masters."


Kind Regards,

 

Charles.C


#3 FurFarmandFork

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Posted 04 October 2018 - 10:13 PM

That could probably work. Key would be to have an aggressive calibration program for your "master" weight so that you can be sure it's good to go.

 

In reality, this is exactly how NIST traceble certificates work. As long as you maintain the chain and verify appropriately, that's exactly what a local calibration place is doing.


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#4 Charles.C

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Posted 05 October 2018 - 01:10 AM

Hi MG,

 

Just as an additional comment. The important location to focus the calibration on will be at the specific target area and the desired accuracy at such point.

 

For example if weighing an object of 5kg with a desired accuracy of +/- 5g, an analog 10kg balance which is calibrated with a certified weight of 5kg would work however if the smallest division is 20g the accuracy would probably be insufficient for most purposes.

 

(Statistically the accuracy interpetation gets somewhat more complex since confidence probabilities are added in).


Kind Regards,

 

Charles.C


#5 Tony-C

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Posted 05 October 2018 - 01:44 AM

Hi MusselsGalore,

 

I would normally be wanting to have at least 2 accredited weights so that you check the operating range/product range rather than a single point. Are you only bagging one weight of mussels?

 

Kind regards,

 

Tony







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