In a supervisory system for detecting abnormal conditions, existing AC electric power supply lines are utilized and a plurality of resonance elements controlled by abnormal condition detectors are connected across the supply lines. High frequency currents of variable frequency are transmitted to the resonance elements over the supply lines and the high frequency current passed through the resonance elements are received by a receiver which is controlled such that it operates only in the regions about the zero points of the AC voltage wave so as to improve the S/N ratio.
A power line communications system has at least one power line upon which noise level varies with time. The system determines quiet periods when noise upon the line is at a reduced level and transmits one or more data packets within the quiet periods, so as to increase data throughput in the system.
In a system for determining the state of each of a plurality of bi-state devices located remotely from a central station, a group of resonant circuits is connected to a multi-frequency excitation source. A bi-state device is then connected to each resonant circuit. When a particular bi-state device is in one position and its corresponding resonant circuit is being excited by its resonant frequency, a maximum amplitude signal is produced by the resonant circuit. When the bi-state device is in the other position, a lesser amplitude signal is produced. The signal produced by each resonant circuit is fed to detection circuitry and in turn to display circuitry. Thus the state of each of the plurality of bi-state devices is indicated by the display circuitry. The two wire line in addition may serve as a transmission medium for a DC control signal used for controlling a remotely located process control valve or for controlling other final actuators.
A data telemetering system includes a plurality of remote transmitter units connected via an alternating current power supply mains to a central receiver. Each cycle of the line voltage is divided into a plurality of time slots, and each transmitter transmits its data in a separate time slot assigned to it. The data is binary multi-bit digital data, and one bit is transmitted by each transmitter in its assigned time slot during each cycle of the line voltage.
A multiplexed data monitoring system for use in monitoring the status of control valves or the like in subsea petroleum well control systems, utilizes an encoder circuit located externally of the control module and composed of passive electrical components, such as inductors and capacitors, to encode switch contact closure or status information into discrete frequency data. The external encoder circuit is coupled by a pair of wires to the control module. The decoder circuitry within the subsea control module applies an alternating current signal of varying frequency to the encoder circuit and by monitoring the phase of the alternating current, the decoder circuitry can recover the data impressed by the switch contacts at the status points, which are also located externally of the control module.
In a remote control system which generates a remote control signal by a temporary short-circuit on the secondary side of a transformer during an influencing period or time span about a zero point transition of the alternating-current mains voltage, a considerable improvement in the receiver-side recognition or detection of the remote control signal can be accomplished by a different determination, in relation to the prior art, of the receiver-side comparison period as concerns its start and duration. There is correlated the comparison period to the course of the receiver-side alternating-current mains voltage before the mains voltage zero transition to be monitorerd. This system may be used in remote control technology using signal transmission on a power supply network.
