Fuel ball detecting method and system with self-diagnosis function

A fuel ball detecting system with a self-diagnosis function, comprising:

• a fuel ball sensor disposed outside a pipeline and comprising a first detecting coil and a second detecting coil winding around the pipeline and set upstream and downstream of a given point on the pipeline respectively;
• an exciting module configured to generate a sinusoidal alternating current exciting signal to excite the first detecting coil and the second detecting coil;
• a resonance bridge detecting circuit configured to obtain a first voltage signal U1 from the first detecting coil and a second voltage signal U2 from the second detecting coil;
• a signal processor connected with the resonance bridge detecting circuit and configured to process the first voltage signal U1 and the second voltage signal U2 by differential amplification, band pass filtering, phase sensitive detection and low pass filtering, so as to obtain a fuel ball waveform signal U0;
• a single chip microcomputer connected with the signal processor and configured to determine whether the fuel ball passes the pipeline according to U0,
• a self-diagnosis module connected with the first detecting coil, the second detecting coil, the signal processor and the single chip microcomputer and configured to detect whether first detecting coil, the second detecting coil, the signal processor and the single chip microcomputer work normally;
• and
• an outputting module connected with the single chip microcomputer and the self-diagnosis module respectively and configured to output a result showing whether the fuel ball passes the pipeline, when the first detecting coil, the second detecting coil, the signal processor and the single chip microcomputer work normally,
• wherein the self-diagnosis module comprises:
• a first detecting unit configured to determine whether the first detecting coil and the second detecting coil work normally by detecting voltages across the first detecting coil and the second detecting coil, and output a first high level signal, when the first detecting coil and the second detecting coil work normally;
• a second detecting unit configured to determine whether the signal processor works normally via a photocoupler disposed on a power source terminal of the signal processor, and output a second high level signal when the signal processor works normally;
• a third detecting unit configured to determine whether the single chip microcomputer works normally by detecting a square wave output from the single chip microcomputer, and output a third high level signal when the single chip microcomputer works normally;
• and
• an AND gate circuit configured to process the first high level signal, the second high level signal and the third high level signal by AND operation to get a self-diagnosis output signal,
• wherein the self-diagnosis module is further configured to determine that the first detecting coil, the second detecting coil, the signal processor and the single chip microcomputer work normally, when the self-diagnosis output signal is a high level signal.