Abstract: A seat belt buckle and latch indicating system employs a seat belt buckle with a Giant Magnetoresistive (GMR) sensor spaced from a magnet above a gap through which a ferromagnetic latch protrudes. The latch may reside at three distinct positions: unlatched, latched, and latched without the presence of a hasp. The latch functions as a magnetic field concentrator with the result that the sensed magnetic field is dependent on latch position. The GMR sensor provides a signal indicating the sensor is working at all times, and provides specific information based on physical positioning of the critical components of the belt and which indicates that the buckle is mated to the seat belt hasp.

Abstract: A seat belt buckle incorporates a spring mounted on the latch. When the latch engages with the tongue of a seat belt, the tongue can move against the spring in response to tension loading of the seat belt while remaining securely latched. This motion due to belt tension is resisted by the spring, with a selected spring constant. A sensor is used to monitor the presence and position of the tongue either directly or by measuring motion of the latch. The position information, which is related to spring compression, is used to determine loading on the tongue and thus seat belt tension.