Edited by Leland Teschler
, also known as acceleration switches, typically open a set of switch contacts in the event of a crash or some other event generating severe g forces. The typical operating principle is to use a mass as a sensing element. Sufficiently high acceleration perturbs the mass in a way that opens switch contacts through the action of a mechanical linkage.
can be designed to switch under specific acceleration-versus-time curves. Sophisticated devices of this sort go into fusing and arming circuits for artillery and ballistic munitions, safety systems on oildrilling rigs, and avionics. One of the most widespread consumer applications for inertia switches is in vehicle fuel systems. There they shut off the fuel pump if the vehicle is in a collision, thus minimizing any fuel leakage and fire hazard.
Automotive inertia sensors typically connect to the electronics controlling the fuel pump and sit somewhere in the dash panel. They also have a manual reset switch. The mass is usually a ball which moves away from a rest position in a crash, thereby triggering a mechanism that opens a switch. In a Toyota inertia switch, for example, a ball sits under a spring-loaded plunger during normal operation. A sufficiently severe crash makes the ball move from under the plunger. A cantilever link from the plunger to a set of switch contacts rotates away from the switch contact point to open the circuit. This signals the engine control unit to power down the fuel pump.