Reseach Of The Method For Detecting Parameters Of UM71 Track Circuit

The jointless track circuit is an advanced control system which is used tocontrol the trains. The rail is used as transmission line for transmitting signals inthis system, thus to meet the need of transmitting multi-purpose controlinformation. The reliability and the quality of the transmitted signals have directrelation to the safety of trains' function. Hence, to detect the parametersperiodically, such as frequency,voltage and compensating capacitors etc, inorder 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' functioncan be ensured.In this subject, methods of detecting those parameters are researched,which is aiming at UM71 track circuit. The main contents of this subject are asfollows, the realization of on-line detecting the frequency of carrier and mod-ulated signals, the voltage of the frequency shifting key (FSK) signal and thevirtual value of the compensating capacitor, while all of them are carried outwithout interrupting the trains' function, and not having to instruct the monitors.How to resolve the technical problem in on-line detecting the parameters ofUM71 track circuit, is introduced in this subject. Due to the FSK signal is theresult of frequency modulation, that is to say, the waveform of the FSK signal isan alternating sine wave, which is come from the carrier that modulated by thelow frequency. When testing the frequency of carrier, it is converted to squarewave which has the same frequency to the carrier at first, then test it directly.While testing the frequencys of the modulated signals, the principle of detectingfrequency by taking count of pulses is adopted, thereby gaining the lowfrequencies from the demodulation to FSK signal, and then its waveform isconverted to pulses which has the same frequency, at last, it can be tested bymicrocontroller. It is convenient to get the circuit to work, and has a goodwaveform, also easy to control. When testing the compensating capacitors,firstly, a sine wave as the testing signal is generated by the function generatingchip, then the testing signal pass the buffer in order to have an insulation withthe follow circuit, secondly, the testing signal is amplified by a power amplifier,and then it acts on the two pins of the compensating capacitors, owing to thefeedback of the testing signal are different if the compensating capacitors aredifferent, so the different feedback of the testing signal are filtered and amplified,then it is rectified, lastly it can be got by the A/D channels of the microcontroller,after conclusive data processing, the virtual value of the compensatingcapacitors can be attained, and it can be displayed by LCM ultimately. Moreover,when testing the voltage level of the FSK signal, it can be rectified directly, thedata processing is similar to the testing of compensating capacitors.