Design of Track Induced Voltage Monitoring System Using True RMS Converter AD736

With the increase in train speed, the Ministry of Railways plans to gradually eliminate ground signals and only use the on-board signal system in the future train operation. The locomotive signal system will be the signal guide for the driver to operate the train. The magnitude of the track induced voltage directly affects the normality of the locomotive signal, so in the monitoring of the operating parameters of the locomotive signal, the monitoring of the track induced voltage is a very important part. The track induced voltage is a small AC signal. The effective value of the AC signal can be measured by the following methods:

    1) Use a peak converter to find the effective value through the crest factor;

    2) Effective value converter of thermocouple bridge;

    3) Use analog operations to form an electronic effective value converter;

    4) Sampling a set of data point by point, find its "root mean square" to get its effective value.

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    Figure 1 Block diagram of intelligent monitoring of track induced voltage

    ISO124 is a low-cost precision capacitance isolation amplifier designed by BB company using new hysteretic modulation/demodulation technology. It is composed of an input part and an output part that are completely symmetrical in the circuit. The laser adjustment process is used to make the two parts completely match during manufacture. Therefore, the output terminal of ISO124 can reproduce the input signal with high reproducibility, so the system access to ISO124 will not affect the integrity of the signal, and it has good high-frequency transient performance. If no external devices are connected, the transmission coefficient is 1: 1. The gain error is less than ±0.5%. The intelligent monitoring circuit diagram of track induced voltage designed by ISO124 and AD736 is shown in Figure 2. In the picture, A1212S-1W provides ±12V power supply for the ISO124 input terminal. This power supply and the output part ±12V power supply are isolated from each other, so as to ensure that the input and output parts of ISO124 are electrically isolated. After the track induced voltage is isolated by ISO124, it is directly input to the high impedance input terminal of AD736, and the Cc pin and the common terminal COM are connected through a DC blocking capacitor Cc. In this way, the output is the effective value of the track induced voltage, which will not Contains DC component.

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    Figure 2 Schematic diagram of track induced voltage measurement. Conclusion my country’s railway locomotive signals mainly adopt phase-continuous frequency shift keying FSK modulation. Currently, there are two main ones widely used: domestic frequency shift signals and French UM-71 frequency shift signals. There are four main center frequencies of the frequency signal, which are 550 Hz and 750 Hz in the downlink and 650 Hz and 850 Hz in the uplink. The center frequency of the French UM-71 frequency shift signal is also mainly

    There are four types, namely downstream 1700Hz, 2300Hz and upstream 2000Hz and 2600Hz. In the monitoring circuit of the effective value of track induced voltage designed by us, the measurement in the frequency range of the above two systems has reached ±3mV, which meets the actual situation on site. demand.