PROBE CALIBRATION

[BANDY]

Ok I got my new PC-DMIS setup, so I am ready to try it out. Got stuck at probe calibration. I am using a 2.5mm x 32mm probe, but when I calibrated I am getting a msg. "Measured probe diameter error exceeds the limits. The diamater should read 0.098 but its actually reads as .9843. Any ideas why is that?

[Wes Cisco]

That is quite normal. Due to flex of extensions and deflection of ruby on sphere the measured diameter will always be a little smaller. What is important is the std. deviation. The lower the better, but if it is more than 0.0004" you can not use the tip, (per B&S instructor). The tip may be bent or dirty or the sphere may be dirty. Try cleaning and re-running. Deviation for a tip that size should be 0.0000" or at the very most 0.0001" I run some very long tips, but I never accept anything over 0.0003". HTH

[kevinb]

Wait, it's reading .9843? Like almost 900 thousanths of an inch big? Sounds like your qualification sphere isn't set right in the calibration window. Make sure the diameter listed for your sphere in the measure window matches the calibration label on your sphere. Might also double check the calibration label with a micrometer.

[Shelley Liebman]

.9843 is the standard sphere diameter in inches, this is probably what you are seeing.
as the first response stated, the important thing is the standard deviation, which I agree should be within .0003"
Just a note, when you post it is helpful to us here to know what version of the software, what type of machine you are running, and what type of probe/head/controller you have.

[#2#]

OK, They are right that the std. deviation is what you need to worry about.

If it is too large (>.0004 inches) then do the following. Check to ensure that the cal. sphere is entered in properly. Check to ensure that the probe is built up as you planned. Clean the tip and the sphere with alcohol and run again.

You can change the limit at which the error messages will appear. Open the probe utilities window. Click on "setup" A new window will open. The sixth line down says "Give a warning during qualification when the standard deviation of the sphere is more than:" I have mine set to .0003 as most of my tips come in at .0001 sometimes .0002.

Right below that line is one that says "Give a warning when the diameter error for the probe tip is more than:" This sounds like the error you are getting. Mine is set to .0098. I am not sure what this affects. I believe PC-DMIS compensates for the error of the probe tip diameter. Perhaps this is the limit of its compensation ability. Mostly it seems this error would be useful to detect improper probe build up (a 3mm tip instead of a 4mm for example).

[Wes Cisco]

Wait, it's reading .9843? Like almost 900 thousanths of an inch big? Sounds like your qualification sphere isn't set right in the calibration window. Make sure the diameter listed for your sphere in the measure window matches the calibration label on your sphere. Might also double check the calibration label with a micrometer.

I need a dose of my own medicine so I pay more attention to those trivial little symbols commonly called numbers. Your calibration sphere is not built correctly. Most likely the diameter is set to zero. HTH

[BANDY]

Thank you for the reply. I am running version 4.0 on a Zeiss Eclipse by the way. How can I change the settings for the calibration sphere?

[bw_bob]

Thank you for the reply. I am running version 4.0 on a Zeiss Eclipse by the way. How can I change the settings for the calibration sphere?

On 3.5 mr2 you can do this in the probe calibration window. You hit measure and at the bottom on the next page you can either add,delete or edit tool. Highlight the tool you want and hit edit. Lets you do what you want from there.

[Paul Barriage]

Size change??? Say it aint so!!!!

Synthetic AND EVEN natural ruby are susceptible to size change. Calibrate right & OFTEN! This is one of the contributing factors to the guaranteed accuracy. The limits you set as warnings are what does this, and as stated above, check your artifact/tool setup and probe build. Just understand though, the size DOES change and is rarely perfect.

[BANDY]

OK. guys I got it now. I had the wrong calibration sphere selected. Thanx for the help.