Dimensional measurement gages are comparator gages generally rated as either short or long-range, the distinction being the operational range of measurement. The technology typically used is a lead screw, glass/steel scale encoder, laser, LVDT or some combination thereof.
The classic short-range comparator is a dedicated LVDT-based machine with a very small operating range. If this comparator is well maintained and operated properly by a skilled operator in a temperature controlled environment, sub micro-inch accuracies can be obtained. The primary drawback of the short-range comparator is that it’s very time consuming. However not all short-range comparators are dedicated or LVDT-based. Some long-range comparators may be temporarily employed in this mode when necessary.
In today’s industrial environment time is money and, in most cases, short-range comparator's level of accuracy may not be warranted. Although Pratt & Whitney manufactures a complete line of long-range comparator dimensional measuring machines for both outside and inside measurement, all of them can also be used in a short-range comparator mode. When used in this way, the system accuracy increases.
The Pratt & Whitney machines most often used in short-range comparator mode are the: