전력선통신

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기존방식의 문제점중의 하나

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Conventional PLC(Power line communication)

1 Communication data flow

2 The principle of communication

The transmitting device(device A) transmits the signal by superimposing the modulated signal of very high frequency(~30MHz) on the wave of power and the receiving device(device C) receives and demodulates the transmitted signal.

3 An example of a problem

  • Communication failure may occur due to the noise from the peripheral devices(device B: vacuum cleaner etc.).
  • Since the modulated and superimposed signal is transmitted to the whole system, the signal works as a noise to the peripheral devices(device B: audio devices etc.) which is not to communicate.
  • When the capacitor(C) is connected to the system AC resistance Xc(capacitive reactance)is as follows.
    C has very high impedance characteristics for power frequency, which is a low frequency (60Hz), and has little effect on the system. However, the carrier frequency for transmitting data is very high frequency. For high carrier frequencies, this capacitor exhibits very low impedance characteristics and acts almost like a short circuit.When the signal is shorted, the signal becomes very weak, making communication difficult.