Abstract: A knock sensor has a substrate having a projection at the center of one surface thereof and a bore at the center thereof, a vibrating plate having a bore at the center thereof and having a plate rigidifying projection means at the center portion of one surface thereof, the central portion being welded to the projection on the substrate, a piezoelectric ceramic element having a bore in the center thereof and electrodes on opposite faces thereof and secured to the other surface of the vibrating plate, and a terminal having a lead projection extending through the bore in the substrate, the bore in the vibrating plate and the bore in the piezoelectric ceramic element and connected to the electrode on the face of the piezoelectric ceramic element which faces away from the vibrating plate.

Abstract: A knocking sensor comprises a casing for receiving a pickup assembly including a transducer, which produces an electrical signal in accordance with engine vibrations, and a connector having at least a single pin electrically connected to the transducer. The casing comprises a threaded projection to be screwed in a screw hole of an engine, and a nut-like periphery to be rotated by a tool. The knocking sensor can be attached to the engine by means of an impact wrench, by rotating the nut-like portion. A plug connected to one end of a shielding code can be plugged in the connector to make an electrical connection between the transducer and a signal processing circuit after the knocking sensor has been attached to the engine, and therefore, the shielding code is prevented from being damaged during installation of the knocking sensor. The use of an impact wrench ensures secure attachment of the sensor, and reduces the installation time.

Abstract: A piezoelectric ceramic vibrator is mounted inside a metal case including a portion adapted for fastening the case to an engine, and the vibrator is adapted to resonate in response to a vibration frequency produced upon knocking of the engine. The output of the vibrator is taken out as a knock output.

Abstract: A knock sensor includes a metal case of a shape that can be easily mounted to an engine, a base of a size that can be fitted in the case and having preliminarily mounted thereon a knock detecting ceramic vibrator, and a cover adapted to be fitted in the case so as to hold the base in place when fitted in the case.

Abstract: In an intercommunication system comprising transmit and receive channels including respective variolossers and being connectable through a hybrid transformer to an external line, the variolossers being so constructed as to allow a high frequency region of the voice frequency band to pass therethrough even when they express a large amount of loss, an AGC amplifier and a manually gain-controllable amplifier being provided in the receive channel, and the control input of the variolossers being picked up from different parts of the receive channel respectively in the transmit mode and the receive mode.