Calibration Determination decision

John Predmore

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#1
I was asked occasionally about what needs to be calibrated or how the interval is determined. We do a mixture of outside calibration service, calibration via built-in software, verify-only, and so on. So I made a flowchart to explain what considerations go into that. This is not a turn-the-crank and the answer pops out, but in essence, there are 4 questions to be answered. I share this here, for anybody who finds this useful.

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Jen Kirley

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#2
Thank you so much for this John! I think some people will find it complicated, but I also think it does a very good job of working through the process so I would recommend people apply it and be patient while doing so: it is made to arrive at the right end decision. :applause::applause:
 

John Predmore

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#3
I should add a footnote. In everyday language, the word Calibrate is used by different people in various contexts, but doesn't always mean the same thing. In an industrial quality setting, my definition of Calibrate versus Verify is that Calibrate includes either or both, comparison to a recognized reference standard and the ability to adjust (as necessary) to improve measurement accuracy. If you cannot adjust or it is more economical to replace, I call that Verify. I often use the example of a bathroom scale as illustration to explain. If you turn the little knob (on a mechanical scale) or step on/off and let the digital scale zero itself, taring is a form of calibration because it actually changes the measurement which results, before and after. The reference standard is nothing on the scale besides the parts of the scale.
 

dwperron

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#4
Here comes the firestorm.......

In the real world of Metrology, industrial or otherwise, Calibration has nothing to do with the ability to adjust. That's why we have a term called Adjustment. Calibration is comparing your tool to a standard of known value.
If you replace a tool without calibration (if it's cheaper to replace than calibrate then replace it...) then you will never know if your tool was in or out of tolerance while it was being used, so why would you waste time and money calibrating or verifying it in the first place?
If you work in an environment where calibration is is a "necessary evil" and close enough is good enough then your plan of action might work.
If you work in the world where you need to be able to demonstrate the validity of your measurements, then this is nowhere near adequate.
 

John Predmore

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#5
I started my footnote with the acceptance that people use different definitions. I actually expected some disagreement because I recognize there are different definitions in common vernacular. I stated the definition I use. That may not align fully with the definition in ISO-17025 or VIM. I guess you could say that is inviting a firestorm. I think defining terms upfront is a fair start for discussion. How else would we begin a meaningful conversation when there are differences of definition?
 

Mike S.

Happy to be Alive
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#6
Here comes the firestorm.......

If you replace a tool without calibration (if it's cheaper to replace than calibrate then replace it...) then you will never know if your tool was in or out of tolerance while it was being used, so why would you waste time and money calibrating or verifying it in the first place?
In the real world you speak of, at least in my real world, we calibrate or verify it in the first place to ensure we are starting off with a good tool and to comply with customer/standard demands.

There are a few items that are cheaper to replace than calibrate, so we consider the risk: how likely is it that one of the pins goes out of tolerance and if it does what is the likely impact? If the risk is low, we replace vs recalibrate.
 

Jen Kirley

Quality and Auditing Expert
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#7
I should add a footnote. In everyday language, the word Calibrate is used by different people in various contexts, but doesn't always mean the same thing. In an industrial quality setting, my definition of Calibrate versus Verify is that Calibrate includes either or both, comparison to a recognized reference standard and the ability to adjust (as necessary) to improve measurement accuracy. If you cannot adjust or it is more economical to replace, I call that Verify. I often use the example of a bathroom scale as illustration to explain. If you turn the little knob (on a mechanical scale) or step on/off and let the digital scale zero itself, taring is a form of calibration because it actually changes the measurement which results, before and after. The reference standard is nothing on the scale besides the parts of the scale.
We have discussed the terms and their confusion many times. The only source I remember posted here (some years ago) that really differentiated the terms was a French standard. You have arrived at basically the same place as definitions go, and you did a very nice job of describing them. Thank you. This subject never ages out of relevance.
:agree:
 
#8
The need to perform calibration is not a function of time, in most cases. Equipment can languish, relatively unused and your chart would have it sent for calibration every 12 months. My boss wouldn’t allow me to spend money like that. Why isn’t the decision based on how many times it was used?
 

Jen Kirley

Quality and Auditing Expert
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#9
Funboi raises a good point. I suggest you refer to your instruments' OEM guidelines as the most relevant advice. Keep aware though, that the OEM is possibly going to advise onthe side of caution. As always, the risk evaluation responsibility remains with the instruments' user.
 
#10
I suggest you refer to your instruments' OEM guidelines as the most relevant advice
The OEM doesn’t have anymore idea on how frequently a device is used - they often recommend 12 months! You have to experiment and get data. A screw plug gauge used to check threads in aluminium will wear less than one used on stainless steel. Yes, it’s work, and you may not want to do what is necessary to generate the data on which to base a decision. However, this talk of time based recalls is only OK when you want to throw money at calibration.
 
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