Is calibration of a weigh scale required?

SGquality

Quite Involved in Discussions
#1
Is calibration of weigh scale required ? One of our departments strongly believes that daily verification with single weight will suffice. Is that true ?
 
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somashekar

Staff member
Super Moderator
#3
Re: Is calibration of weigh scale required ?

Is calibration of weigh scale required ? One of our departments strongly believes that daily verification with single weight will suffice. Is that true ?
A regulatory requirement may be applicable for periodic calibration....
 
W

w_grunfeld

#4
Re: Is calibration of weigh scale required ?

In theory not required in most cases, except if used to verify compliance /decide to accept or reject a product. In this case checking with one weight is NOT CALIBRATION.
iN PRACTICE, 9 out of 10 auditors would write up a discrepancy claiming you can't ensure that it won't be used one day by someone for acceptance check.
Just have it calibrated and avoid the hassle:bigwave:
 

Big Jim

Super Moderator
#5
Re: Is calibration of weigh scale required ?

Have a good read of ISO 9001:2008 7.6a, and pay especial attention to the line above a "Where necessary to ensure valid results" as well as "measuring tools shall be . . . calibrated or verified, or both, at specified intervals . . . against measuring standards traceable to national or international standards . . . "

If it is needed for valid results, it needs to be calibrated.

If it needs to be calibrated, it needs to be done often enough that the calibration cannot be called into question.

Common sense should tell you that verifying a scale with one weight, one point within its range, is not calibration, or at most, is limited calibration.

If the weight set used for calibration is not traceable to an international or national standard (in the US, usually NIST) it is of no effect.

But it all hinges on "Where necessary to ensure valid results".
 

dgriffith

Quite Involved in Discussions
#6
You might ask, if I don't care about the scale accuracy and results, why do I even need the make the measurement?
In any case, after the weigh scale is calibrated, and before its next calibration, you can use a single mass, which is also calibrated, as a check standard during the time interval between calibrations. Use an appropriate SPC method to demonstrate no shift in sensitivity, which will give you confidence in weight measurements.
Some labs use one before every measurement, some at the first of every shift, some longer.
The greater the scale range, the heavier the mass needs to be--can't be putting 5 lbs. on a 100 lb. scale to check sensitivity.
 
#7
Is calibration of weigh scale required ? One of our departments strongly believes that daily verification with single weight will suffice. Is that true ?
Calibration is the science of knowing how far "off" you are when you make a measurement = the variation which is attributable to the measuring equipment. As has been stated, a single point isn't going to give you that - so whomever is calling THAT "calibration", clearly isn't competent in the terminology. You ARE allowed - to get "valid results" - to use a transfer standard (set of known weights in a range of values). This is perfectly acceptable but it's verification, not calibration since no measurement variation is taken into account. You should perform this type of check either side of the value(s) you normally weigh to ensure you understand the characteristics of the scales - are the results linear in nature, for example.
 
Last edited:

gpainter

Quite Involved in Discussions
#8
Most states require that any thing sold by weight or verified by weight require at least yearly calibration. Most counties have a local weight and measures person that will do it on a yearly basis for free (if you sell by weight or measure) or little cost. Shipping scales are just one example in manufacturing, in the test lab- some tests are based on the weight of the product, truck scales., etc
 
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