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Tutorial - Form Measurement

Gauge Range, Resolution and Linearity are important for Form Measurement.

Often, a large range and excellent resolution are required, this means that the calibration method is very important.

Some considerations are:

a) Gauge range , Resolution and Linearity
b) Calibration Method / Ball Radius
c) Stylus Type & ensure Stylus tip is suitable
d) Ensure measurement is within the calibrated range
e) Ensure part does not contact the stylus tip at a position which was not covered by the calibration. This means that the stylus length, the stylus tip radius and the calibration ball radius must be considered.
f) Ensure stylus does not 'flank'
g) Component alignment and fixturing.

For a straightness result the measured data can be fitted to an LS line the resultant Pt value is the maximum deviation from the LS line i.e the component  straightness error. 

The measured data can also be fitted to an MZ (minimum zone) reference. The minimum zone reference is defined by a pair of straight, parallel lines which just enclose the entire profile such that the distance between the lines (the zone) is a minimum.  The displayed reference line is the mean position between these two lines and to which all parameter calculations are referenced.

The Pt value displayed is the straightness error. Usually the MZ result will give a smaller straightness error than the LS result over the same profile.

It must be said that using an MZ reference is not as stable as an LS reference due to its susceptibility to random peaks and spikes.

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