Abstract: A small-sized, reliable, low-cost acceleration sensor includes a working mechanism having a large joint surface. In this respect, an acceleration sensor 1 is arranged so that a diaphragm portion 2D is formed on a (100) face of a plate of single crystal silicon. The four corner portions of the joint surface 2A of a square frame are expanded in the center direction of the plate of single crystal silicon so as to form expanded portions 2B. Moreover, the (100) face of the square plate of single crystal silicon is covered with a mask having at least an octagonal opening 10E before being subjected to anisotropic etching, so that the expanded portions 2B directed to the center portion are formed in the respective four corner portions of the plate of single crystal silicon.

Abstract: An acceleration sensor is based on a semiconductor technique which is suitable for mass production. The resulting acceleration sensor is small in size and high in precision. The acceleration sensor includes a stationary section, an acting section to which a force is applied in response to acceleration, a flexible section through which the stationary section is coupled to the acting section, a plurality of distortion sensing elements coupled to the flexible section, a first weight having a bottomed hole which is gradually smaller in width towards the bottom of the hole, the first weight being coupled to the acting section and a second weight, greater in specific gravity than the first weight, coupled to the bottom of the hole of the first weight.

Abstract: A counter electromotive force due to electromagnetic induction is generated on interruption of a current if an actuator 10 is in a normal state. An output signal generated by the counter electromotive force and a pulse signal which is generated from the fall of an input signal applied to the electronic switch are applied to an AND logical circuit 90 to determine whether or not the actuator is defective.