Abstract: A transmitter for repeatedly transmitting a measured value in the form of a digital signal through a two-wire transmission line, includes a receiving unit for receiving a digital command signal from a communicator through the two-wire transmission line, and a processor for sending out a response signal in response to the command signal upon reception thereof. The measured value is sent using a newest measured value after repetitive transmission of the measured value is interrupted. The measured value is transmitted from the transmitter by a change in current supplied to the two-wire transmission line, and reception of the command signal is performed by a change in interline voltage of the two-wire transmission line.

Abstract: A receiver for receiving a reception signal defining a measured value is connected to a two-wire transmission line used for transmitting a digital command signal from a communicator, a digital measured value signal from a transmitter, and a response signal responding to the command signal. The receiver includes a timer for discriminating that a nonsignalling state of the two-wire transmission line has continued for a predetermined period, and a CPU for validating a specific period of a reception signal received after the discrimination operation of the timer.