Abstract: A rectifying and integrating circuit, particularly in a knock-detection system for an internal combustion engine, comprises an operational amplifier, an integrating capacitor with one side connected to the amplifier output and its other side connected to the signal input of the amplifier, a first rectifying device connecting the amplifier output to the one side (i.e. output side) of the integrating capacitor, and a second rectifying device connecting the amplifier output to its signal input. The signal input current is balanced by feedback through either the first rectifying device and the capacitor or through the other rectifying device, depending on the polarity of the input. Integration occurs on one polarity. In the absence of a rectifier amplifier preceding a separate integrator, errors due to input offset voltages of the rectifier amplifier are avoided.

Abstract: A machine guard installation makes use of a proximity detector system including a passive time circuit on the guard. The timed circuit includes a coil which is magnetically coupled to a further coil only when the guard is in its operative guarding position. The further coil forms a part of a positive feedback loop of an amplifier in an active detector circuit, which oscillates only when the coils are coupled as aforesaid.