[Ri...] Posted February 12 Share Posted February 12 I have not seen an uncertainty this high before, is this a typo? Maximum Uncertainty of Length Measurement = 0.04 + L/7000.00 [µm] Temperature 20.00 °C Two of the four certs read: 0.04 + L/7001.00 [µm] Later in all the certificates it reads: MPE = +/- (0.7 + L/400) µm Any assistance is appreciated. Link to comment Share on other sites More sharing options...
[Da...] Posted February 12 Share Posted February 12 That would be an earth-shattering low uncertainty, not a high one. And yes, it’s a typo. The last one makes more sense. Link to comment Share on other sites More sharing options...
[Ri...] Posted February 12 Author Share Posted February 12 To make sure I am not seeing something new, this is a screenshot of page one of a certificate (Company info removed). (Capture.PNG) Page 3 is Capture2.PNG, showing the typical Uncertainty calculation.Capture2.PNGCapture.PNG Link to comment Share on other sites More sharing options...
[Ri...] Posted February 13 Share Posted February 13 Please sign in to view this quote. This is the uncertainty of the measurement of the gage used to calibrate your CMM. Every measurement in the world has uncertainty in it, but certified labs will actually state their measurement uncertainty. When you look at your "trumpet" charts, you will see the measurement uncertainty for each measurement taken (it's the error bars for each measurement). Capture.PNG Link to comment Share on other sites More sharing options...
[Ri...] Posted February 13 Share Posted February 13 Please sign in to view this quote. Accuracy is NOT the same thing as uncertainty. https://www.npl.co.uk/resources/q-a/dif ... ncertainty Link to comment Share on other sites More sharing options...
[Ri...] Posted February 19 Author Share Posted February 19 Please sign in to view this quote. Are you saying that this "0.04 + L/7000.00 [µm]" is for accuracy? Link to comment Share on other sites More sharing options...
[Ri...] Posted February 19 Share Posted February 19 Please sign in to view this quote. No. Once again accuracy and uncertainty are not the same thing. There is uncertainty in every measurement taken - no exceptions. The "0.04 + L/7000.00 [µm]" is the statement of uncertainty for the reference measurements taken on the length standard that the Zeiss technician uses. For example if the certification of the length standard said that the first measurement was 50.005159mm that would mean that actually the first measurement is 50.0051589mm ±0.047144µm. Meaning that the true measurement is somewhere between 50.005112mm and 50.005206mm. Once again, you can never know the absolute true measurement. We can only quantify our uncertainty. For most customers and most calibrations/certifications, these values typically have zero impact on you and mean nothing to you, but for calibration/certification labs themselves they mean everything. We ourselves are a calibration/certification lab and we have to take all kinds of factors into our stated measurement uncertainty, and one of the factors is the uncertainty of the calibration of the equipment itself. So if Zeiss (or whoever) brought in a gage that itself had a huge measurement uncertainty, it would have a huge impact on our own measurement uncertainty. To geek out for a moment, we recently had a length standard certified at NIST, and we were blown away by the work. The quantify everything, and by everything I mean things like the index of refraction for air pressure. Lol. World class stuff here. Link to comment Share on other sites More sharing options...
[Ri...] Posted February 20 Author Share Posted February 20 Thank you Richard Shomaker.2 for taking the time to educate me on this. Link to comment Share on other sites More sharing options...
[To...] Posted February 20 Share Posted February 20 Please sign in to view this quote. Richard is good at this. Link to comment Share on other sites More sharing options...
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