brown & sharpe Global 121510, User Manual, Page: 71 / 144

System Options
Global User Manual
6-9
System Options
Measuring with an Electronic Probe
Measurement points are recorded when the stylus is deflected
enough to either break mechanical contacts or generate enough
force to trigger pressure sensitive circuitry. This generates a
signal to the controller, which latches the counters and records
the “point”. For manual measurements, the operator must be
careful to take measurement points at a velocity which will not
create damage to the probing system.
The arrangement of the contacts does cause slight errors in
probing. These are reduced during probe qualification. However,
the longer the probe tip extension, the larger the pre-travel error
and the more residual error is left after probe qualification. Also,
longer probes tend to be not as stiff as shorter probes. The more
a stylus flexes or deflects, the lower the accuracy. Therefore,
probing with very long stylus/extension combinations should be
avoided.
Probe hits (also known as “points”) should be taken perpendicu-
lar to the part surface wherever possible. If hits are not taken
perpendicular to the part, skidding may occur. Skidding (probe
tip sliding on the part as probe contacts are disturbed) produces
inconsistent and non-repeatable results. If probe hits are taken
within ±20 degrees of perpendicular, skidding errors will be
much less than one micron.
· Clean the stylus with alcohol
· Clean reference sphere
· Verify stylus is screwed in completely
Verify reference sphere is securely bolted to granite