Probe trigger versus probe overtravel force
A touch-trigger probe can be thought of as a very repeatable, normally closed, contact switch.
When the probe touches a part, the contacts go open circuit at the trigger force. At this point the output signal from the probe is used to trigger a control system to simultaneously read the CMM measuring scales to give the coordinates of the point taken. The CMM will then stop and back off the part. However this cannot happen instantly. The CMM has to decelerate from the measuring speed so the probe will ‘overtravel' whilst the machine slows down, stops and backs off the part. This is when the probe is subjected to the probe's overtravel force.