Electronic Weighing Scale Calibration Tolerance

[WEAVER]

We have a new Electronic Weighing Scale used for counting good products in order to check if there was no mixed defective as per machine count. My question would be how to provide calibration test points and tolerances (or should it be calibrated at all?) I have no process tolerance, only that the minimum weight of the product we count is about 7~8 mg., the resolution of the counter is 2 mg and the max is 150g. Minimum countable weight : 0.25 mg The users manual of the scale has a test weight calibration procedure where the weighing scale would have error alarm if the error reaches 1 percent at span calibration. Can I use 1 percent tolerance for the entire operating range and what would be my lowest test point? The exact model of the scale is VIBRA CUX150 .
I tried to read NIST handbook 44 but i can't understand it much, sorry
Thank you in advance, I don't know where else to ask

 

[Jen Kirley]

Good day Weaver, I am sorry about the delay in this response.

I often suggest starting with the OEM manual, as you have done. The recommended 1% tolerance makes sense, but I want to note that scale calibrations are often done in a series of segments within the scale's range (see page 55 in NIST Handbook 44). See also Section UR (starting on page 74). Load is on page 78, Table 8.

Does your scale identify its class? I don't use NIST Handbook 44 often but it looks like relevant sections for class is in Tables 7a and 7b. on page 75. Accuracy is described on pages 49, 55 (S.6.6. and N.1.), see also 64 - 68 (T.1., Table T.1.1 and Table 5, also section T.N.).

Don't forget to ensure the scale remains balanced. Does it have an indicator window with a little bubble and a circle? If so, ensure the bubble is within the circle.


You did not describe what industry you're in, so I can't advise more specifically than this.

I hope this helps!