Abstract: In an optical network some optical nodes are fitted with optical switches. The optical switches support the optical coupling and decoupling of the optical nodes and the remainder of the optical network. Electrical power supply failures to a node result in the node being optically decoupled from the remainder of the optical network thereby allowing the remaining nodes to continue normal operation.

Abstract: A metal detector uses a transmitting search coil inductively coupled to a receiving coil for detecting the presence of metal objects near the surface of the ground within the field of the coils. An oscillator generates a signal transmitted by the transmit coil, and the signals detected by the receive coil are coupled to the signal inputs of two synchronous demodulators. The output of the oscillator also is applied at different phases to the reference signal inputs of the two synchronous demodulators. The outputs of these demodulators then are passed through low pass and bandpass filters having a low cutoff frequency which is higher than the highest frequency components generated in the synchronous demodulators due to ground effects.