PLATTENPOSITIONSMESSSYSTEM

A method and apparatus is disclosed for calibrating a gap sensing probe (12) in a refiner having first (76) and second (80) grinding plates facing each other and supported by respective first and second plate holders, each grinding plate having a face (78, 82) defining a grinding gap (86). The gap measuring device, which is secured within one of the plates, includes a sensor probe (12) for measuring gap width data having a substantially cylindrical tip (14) with a flat frontal portion (16), an attached conical portion (18) and a longitudinal axis (20) therebetween. A cable (22) is electrically connected to the conical portion of the probe, for transmitting the gap width data. A protective sleeve (24) can be positioned around and contact the cylindrical tip, wherein the flat frontal portion of the tip is exposed through the sleeve. A substantially crucible-shaped ceramic housing (28) having a closed front (30), an open back (32) is provided, wherein the flat frontal portion of the tip abuts the front of the housing and the cable protrudes from the rear of the housing. A threaded mounting adapter (42) is situated around the housing and an adapter plug (60) is situated within the mounting adapter. The housing, the mounting adapter, and the adapter plug have flanges (38, 48, 68) and shoulders (52) which interact so as to prevent movement of the housing. In the preferred embodiment, the probe is calibrated from the rear of the housing by turning the probe by the threaded mounting adapter. The calibration can be completed without actually measuring the plate gap width by rotating the probe through threads which are of a known and predetermined width.