Sensor for use with air bag inflator and method for making

Claim 1

A pressure switch system for providing a low pressure warning, said system comprising a first gas mixture stored in a container of an air bag inflation system, said first gas mixture selected from the group consisting essentially of argon, nitrogen and helium, a housing received in the container, a pressure responsive snap acting disc having first and second opposite face surfaces mounted in the housing, the disc movable between first and second oppositely dished configurations, an electric switch operatively connected to the disc to open and close an electric circuit in dependence upon the configuration of the disc, the first face surface of the disc being exposed to the first gas mixture, a reference gas chamber mounted on the housing, a second gas mixture contained in the reference gas chamber, said second gas mixture selected from the group of gases for the first gas mixture and including at least one additional gas, the second face surface of the disc being exposed to the second gas mixture, the second gas mixture being filled to a lower pressure than the pressure of the first gas mixture at any given temperature, the pressure vs. temperature curve of the first gas mixture having a first slope and the additional gas having a pressure vs. temperature curve with a slope that is steeper than the slope of the pressure vs. temperature curve of the first gas mixture so that the slope of the pressure vs. temperature curves of the first and second gas mixtures are essentially the same.