Abstract: A detector detects a rotational speed of a rotating object. The detector includes a closed magnetic circuit having a magnet therein, and detects the rotational speed according to a magnetic flux alteration in the closed magnetic circuit. The detector comprises a cylindrical rotor switch, which rotates together with the rotating object, and a fixed sensor device having a magnet, an electromagnetic coil and claws constituting a magnetic switch. At least two magnetic switches are provided in the closed magnetic circuit in order to increase the flux alteration in the circuit and thereby to enhance a detection accuracy.

Abstract: A vibration and acoustic wave detecting device employing a piezoelectric element has a construction such that a piezoelectric element comprises a first surface electrode disposed on a first surface of the piezoelectric element and having a first output terminal of the detecting device, a second surface electrode opposite to the first surface thereof, a side electrode disposed to surround a side surface of the detecting device and having portions respectively extending over the first and second surfaces, the three electrodes being disposed separately from each other, and a resistor disposed on the piezoelectric element to extend across the first surface electrode and the side electrode and to be connected therewith electrically, and the piezoelectric element further comprises a conductive member which is attached to the piezoelectric element to be in contact with the second surface electrode and the side electrode and hence to provide electrical connection between both electrodes.