Dynamic Sigma for Stylus Re-Qualification

[[Jo...]]

Can anyone tell me what the significance of the Dyn. Sigma result is for a stylus qualification/re-qualification and if there is a max tolerance or threshold for what CALYPSO deems is a "passing" qualification? Not sure if it makes a difference, but I have CALYPSO set to inches on my CMMs.

Thanks!

Dyn. Sigma.jpg

[[Ke...]]

The limit value for what Calypso will accept as passing is actually something you can control (or even turn off), in the stylus qualification value under "Set Limit Values".
You can also change or turn on limits for radius, temperature, and positional values as well. I've attached snips from the Calypso manual regarding what Dynamic qualification does(a better and more concise description than I could give), and what the Sigma value means(the best explanation of where this value comes from that I have received)

[[Ri...]]

I would recommend to either view the Stylus Qualification results in MM to the 4th decimal place, or in IN to the 5th decimal place. 0.0001" would be a pretty significant sigma value.

[[Jo...]]

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Hi Kevin,

This is great information and very helpful! But is there a recommended limit value (min/max) to ensure a more accurate and reliable qualification?

[[Ri...]]

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We teach 30% of your MPe. So if your machine has an MPe of 1.5µm, then you would typically say you want your Sigma to be less than 0.45µm or 0.00045mm or 0.000018".

Is the 30% a hard rule? No, as I would apply that to what I would call a standard stylus system (a robust stylus system). Your Sigma value will naturally go up as your stylus system because less and less robust.

If you are seeing high Sigma values with a reasonably robust stylus system, it is most likely damaged/worn.

[[Ke...]]

I don't know if there is any official documentation, because there is some dependence on the type of sensor you are using, and the type of probes. For me, using a Vast Gold probehead with conventional probes (nothing on extremely long extensions, no probes with very thin long shafts, no hollow hemisphere styli, disk styli, cylinder styli) I look for a Sigma value of 0.002mm or less, usually seeing around 0.0005mm. I typically leave the limit value at the Calypso default or even disable it entirely, instead looking at the calibration values myself and use my judgement based on the probe design and the use-I generally look at Sigma more to determine probe cleanliness and health. The Dynamic tensor is primarily used with high speed scanning, so if I am not doing any high speed scanning in the program I may choose to move forward seeing, for example, a 0.005mm value, even though it is above my nominal "limit" if I determine the probe is not damaged or dirty(ITP probes for example almost always have a higher sigma value).

[[Jo...]]

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Is that for both Sigma and Dyn. Sigma results?

[[Jo...]]

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Is that for both Sigma and Dyn. Sigma results?