Abstract: A proximity sensor adapted to sense the presence of metal is located in a processing system for producing pressed board product, such as oriented strand board (OSB), or the like, at a position to detect the presence or absence of product on a metal transfer screen when it is delivered to the unloader station. The sensor is carried by a floating support device that maintains the operating face of the sensor level. The operating face of the sensor is disposed a predetermined distance above the bottom of the support device whereby elevation of the support device and the mounted sensor by a passing board product displaces the sensor beyond its effective detection range to indicate the desired presence of product. Alternatively, when product is missing, the electric signal emitted by the sensor may be operatively connected to a sensible alarm or may be operative in the system control to automatically terminate system operation so that the detected malfunction can be corrected.