Seat Occupancy Detection (OC3 MAT)

Seat Occupancy Detection (OC3 Mat)





Legislation in the USA makes it imperative for the system employed to detect occupancy of the front passenger seat to distinguish between occupancy by a small person and use of the seat to anchor a child restraint system.





A straightforward seat occupancy detector recognizes a certain weight (>12 kg) as proof that the seat is occupied. In order to meet legislative requirements, the seat occupancy detector (SBE) was developed into an intelligent occupant classifier (Occupant Classification OC). This was achieved by means of the following measures:
^ By a larger number of sensor elements
^ By detection over the entire seat area
^ By an intelligent electronic analyzer
The OC3 mat is capable of distinguishing between a one year old child in a childs seat and a light person (approximately 45 kg).
The OC3 mat is integrated into the seat area of the passenger seat. The OC3 mat consists of conductors with pressure dependent resistor elements (FSR, or Force Sensitive Resistance elements). The conductors are connected to the electronic analyzer.





The FSR elements are wired in such a way that they can be sampled individually. When the mechanical load on a sensor element increases electrical resistance decreases and the measurement current changes accordingly.
By analyzing the signals from the individual sensors, the analyzer maps the occupancy of the seat surface and can identify the local concentrations of weight. The distances between the areas and the concentrations of weight indicate whether the occupant is small or large. An algorithm computes the weight class and decides whether the seat is occupied by a person or by a childs seat.





The width between the hip bones is related to the weight of the person. Consequently, the analyzer can distinguish between a light person and a heavy person.
The electronic analyzer of the OC3 mat sends a telegram to the SBSR. If the occupant is identified as a child (based on weight) in a childs seat, the airbags on the passenger side are deactivated. The SBSR sends a telegram to the SGM, and the SGM responds by activating the airbag illuminated indicator. The airbag illuminated indicator lights up to indicate that the airbags on the passenger side have been deactivated.