ON and OFF information signals are transmitted through an AC voltage distribution line via a single frequency carrier signal during a period of time in each cycle of the AC voltage when the information signal is in the ON condition and during another period of time in each such cycle when the information signal is in the OFF condition. A receiver receives the carrier signal from the distribution line synchronously with the AC voltage and determines the ON and OFF condition of the derived and received signal.
A remote meter-reading system interrogates meter stations over power lines and receives encoded meter readings over the power lines in synchronism with the power line frequency by superimposing a digitally modulated signal over the 60-Hz power frequency. The central control station transmits at a data rate of 60-baud and receives at a data rate that is 60-baud or a submultiple thereof, to reduce the demands on the remote meter station transceiver as compared to those on the central control unit transceiver. The bit clock at the central control unit and the meter stations is derived from the 60-Hz power line phase available at each station. Each meter station achieves message synchronization by continuously monitoring the data bit stream for a preset synchronization code and thereafter treats the following 21 data bits as address and function codes. Each meter station that is addressed responds at the data rate designated by the function code by transmitting with a message including the address and function bits for comparison at the central control station with that originally sent to facilitate error detection, and the meter reading encoded according to an error detecting code. A binary data bit is represented by quadrature phase lead and lag relative to reference phase of the character.
A power line carrier system is coupled to two or more phase wires of an electrical power transmission line by transformers and coaxial transmission lines. Each phase wire to be used is provided with a coupling capacitor which is respectively coupled to one end of a coaxial line through an impedance matching transformer. The other ends of the coaxial lines are coupled to the carrier system through one or more isolation transformers. Use of this coupling arrangement eliminates the previously used, exposed unbalanced lines, and their inherent disadvantages. Where a plurality of phase wires are used, this arrangement permits the carrier to be coupled to the phase wires with various relative voltage magnitudes and various relative phases.
For transferring signals relative to an electric machine provided with a three-phase power supply cable with three phase conductors, there is applied a signal to be transmitted to a first point in the three-phase cable between anyone of the phase conductors of such cable and both of the other phase conductors taken conjointly, and a reception signal is picked up in another point in said cable between anyone of the phase conductors of such cable and both of the other phase conductors taken conjointly. Preferably, similar capacitors are associated with each of the phase conductors in the cable at each end thereof, a galvanic separation transformer being disposed between such conductors, and the transmitter and the receiver, respectively, and an inductance being disposed between such transformers and conductors.
An identification system, consisting of at least one stationary element and at least one movable element or token, the first element having a first induction coil adapted to generate a magnetic alternating field and being connected to a source of alternating current, and to a detector for detecting variations of the electromagnetic field, the detector being adapted to compare the detected patterns, the second element having a second induction coil adapted to pick up the field of the first coil and being connected to a rectifier circuit adapted to rectify the induction voltage of the second coil, a capacitive storage device being provided for smoothing the rectified voltage, a control circuit being fed by the rectified voltage and receiving, at an input terminal, the ac voltage induced in the second coil, the control circuit having an encoding deive adapted to produce, at an output terminal, code signals identifying the second element, these code signals being used for actuating a switch which, in one condition, short-circuits the second coil. This system is characterized in that the capacitive storage device is of a small capacity, in particular an integrated or intrinsic capacity of the circuit of each second element, in that the rectifier is a full-wave pg,2 rectifier bridge, two opposite corners thereof being connected to the respective ends of the second coil and one thereof also being connected to the signal input terminal of the control circuit, and in that the switch means is adapted to short-circuit one arm of the bridge which is connected to that end of the second coil which is not connected to the signal input terminal of the control circuit.
A powersaving room security system including a switch connected to a door locking system which generates a lock signal congruous to proper locking of the door. A central control unit produces control signals which can be transmitted through the room AC lines. The control signal corresponds to the existence of the lock signal. Module units are respectively connected to each of the various electrical wall switches and receptacles in the room and respond to the control signals for correspondingly controlling the respective receptacles and wall switches. In this way, lights and appliances in the room can only be permanently energized from the room AC lines when the door of the room is properly locked. At the same time, the system provides an energy saving system by turning off all appliances and lights which the guests may have left on without leaving the room.
