How do you make a ton of pickle relish? You need something like a giant food processor. The blades for such a machine are mounted very close together to create a fine cutting mesh. Should the blades interfere, an entire run of product would have to be scrapped because of the chance that metal shavings might be present. The shape of the blades must be measured on a regular basis to insure that the blades are in the correct position. How can the blades of a dicing machine be checked quickly and accurately?

A fixture is made to hold the blade under test. 16 LVDT displacement sensors are positioned above and below the blade on separate mountings. The LVDT mountings are movable and bring the LVDTs in contact with the blade.

A good blade is used as a standard, and the LVDT readings for it are recorded as a reference. When a used blade is tested, the LVDT readings must be within a certain tolerance of the standard.

To create an automated gaging system, a PC interface to the LVDTs is needed. Each LVDT sensor requires an AC excitation and returns an AC signal that is proportional to displacement. The AC signal must be converted to a digital value by the PC interface, and scaled into engineering units of distance, usually thousandths of an inch.

The software in the PC requests readings from all 16 LVDT sensors and compares the values to the readings from the standard blade. The differences are calculated and checked against the tolerances for that particular blade. An alarm indication is given on the PC screen if a measurement is out of tolerance.