Weight Calibration Standards - External Calibration Frequency

BradM

Staff member
Admin
#11
The first question is how often the weights are used. The next question is how they are stored and how they are handled. These two things will generally drive that answer.

A weight used weekly or daily, I would say needs to go on an interval not more than one year, and less is preferred.

If gloves or tweezers are not used to handle them, then the weight changes the minute they are picked up, because of finger oils.

Weights used once or twice a year, stored in a locked cabinet in a controlled environment, and always handled wearing gloves or using tweezers, I would say can be pushed up to five years.
I was going to post, until I noticed that Hershal captured what I was going to suggest essentially verbatim. I have watched weight sets from the same manufacture, same class, and same material (mass standards are made with different material, and have different expansion and such), yield quite different as-found error during routine calibration. The primary variable is who is using them, and the difference of how they are handled. Weights used by metrology personnel on a nearly daily basis have less error than weights used by lab personnel used on a weekly/ monthly basis. My point is that handling/ storage/ gloves/ etc. make a big difference. Whether they "lift/lower" the weights on the pan, or "drag" them can make a difference. Even depending on how often they replace the gloves they use.

The key to deriving the optimal re-calibration interval is the data. However, until you can generate enough history to make decisions, I would go with Hershal's recommended intervals.

It's important the users understand how much they can affect mass standards by improper handling.
 
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DRAMMAN

#12
This is the age old calibration question.....how long can I stretch out my intervals to cut cost? Every situation is different. I think you should start by researching a few things.

1. How is the calibration process conducted?
2. In lui of data, talk ot your weight standard supplier to get their advice on how the weights can go out of calibration. What are the common causes for weights going out of calibration? What is a typical calibration frequency?
3. Talk to your calibration service provider to find out what the typical intervals are? What would they recommend? What do they commonly see as the reason weights go out? How frequently do they see weights out of cal? A good calibration service wants to build a relationship and will be more than willing to help you optimize your cal intervals.
 
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