Active versus Passive Scanning for Multi-Point Measurement
There are two available contact-scanning technologies: passive and active. Passive scanning probe heads use springs to hold the stylus in its neutral position and strain gauges to measure deflection.
Both record surface data based on the movement of a stylus connected to a scanning head. The difference is what goes on inside the scanning head. The distinction between touch-trigger (single point) measurement and scanning is well known. Touch trigger has been described as a “woodpecker” approach measure a point, move to another location, measure again, and repeat until the job is done. The surface or feature condition between the points that are actually measured may be estimated by interpolation, but significant deviations can be missed. Also, because each measurement is a discrete operation and the measuring head must be repositioned to measure the point, the process can be very slow. Scanning, on the other hand, is accomplished with a fluid and continuous movement that can quickly and accurately measure hundreds or thousands of points along a path as the stylus moves across a surface. But while all scanning technologies offer advantages over single-point measurement, all scanning probe heads are not the same.