FSK transmission circuit for remote sensors integration in distributed measurement systems

In this paper is presented an innovative design and the practical implementation of a communication circuit intended to be used for long distances transmission of the signals from sensors. The circuit is suitable for integration within the conditioning modules that are used for processing of signals from sensors that are connected to remote data acquisition systems. Regarding his structure, the proposed circuit is composed by two modules: the transmitter and the receiver. The transmission part operates with FSK (Frequency Shift Keying) modulation technique having two discrete transmission frequencies of 400kHz and 800kHz respectively. The receiver part of the circuit is implemented as an asynchronous FSK demodulator. The maximum data transmission rate obtained with the proposed circuit is around 100kbits/s but this value can be improved by using more rapid circuits and increasing the carrier frequency. By using the robust FSK modulation for sensor´s signal transmission, the circuit achieves an improved immunity to electrical noises and spurious signals. This is an important advantage because interference problems are very frequently meet in the industrial environments where operates remote data acquisition systems. Another advantage of the proposed circuits is the possibility to multiplex signals from multiple sensors in order to be transmitted on the same physical channel.