The Frequency-Shift Keying Signal Demodulation Research On LabVIEW

The jointless track circuit is an advanced control system which is used to control the trains. The rail is used as transmission line for transmitting signals in this system, thus to meet the need of transmitting multi-purpose control information. The reliability and the quality of the transmitted signals have direct relation to the safety of trains'function. Hence, to detect the parameters periodically, such as frequency,voltage and compensating capacitors etc, in order to inspect if the track circuit and signal equipments are working good. Finally, the hidden disasters can be avoided, and the safety of the trains'function can be ensured.In this subject, methods of detecting those parameters are researched, which is aiming at the characteristics of track circuit signal. The main contents of this subject are as follows, the realization of on-line detecting the frequency of carrier and modulated signals, the voltage of the frequency shifting key (FSK) signal, while all of them are carried out without interrupting the trains'function, and not having to instruct the monitors.How to resolve some technical problems of track circuits parameters on-line tested in electrical railway is introduced in this subject. Because the track circuit signal is a phase-continuous FSK signal, ignal,it's waveform is two AC sine signal of alternating i.e. upper frequency and lower frequency which was generated by low frequency modulating middle frequenc. track circuit signal test exist lot of interference in electrified railway , such as interference with the return of traction current; signal transmission cables affected by the emotional traction network system, capacitive coupling of the interference; exercise of electric locomotive on the electric power system to the following track circuit induction of inductive interference. In testing upper frequency,lower fr- equency,and modulating frequency, the EMD algorithm is adopted, EMD algorithm can extract a variety of frequency information from strong background noise reliably.Then the upper frequency and lower frequency can be obtained directly combined with FFT transform. The formation of system test program is based on LabVIEW virtual instrument platform environment.