Patent Number: 
Section: claims

1. A fuel ball detecting method with a self-diagnosis function, comprising:exciting a first detecting coil and a second detecting coil of a fuel ball sensor disposed outside a pipeline by a sinusoidal alternating current, wherein the first detecting coil and the second detecting coil wind around the pipeline and are set upstream and downstream of a given point on the pipeline respectively;obtaining a first voltage signal U1 from the first detecting coil and a second voltage signal U2 from the second detecting coil;processing the first voltage signal U1 and the second voltage signal U2 by differential amplification, band pass filtering, phase sensitive detection and low pass filtering by a signal processor so as to obtain a fuel ball waveform signal U0;determining whether the fuel ball passes the pipeline according to U0 by a single chip microcomputer;determining whether the first detecting coil, the second detecting coil, the signal processor and the single chip microcomputer work normally; andoutputting 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 determining whether the first detecting coil, the second detecting coil, the signal processor and the single chip microcomputer work normally comprises:determining 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 outputting a first high level signal, when the first detecting coil and the second detecting coil work normally;determining whether the signal processor works normally via a photocoupler disposed on a power source terminal of the signal processor, and outputting a second high level signal when the signal processor works normally;determining whether the single chip microcomputer works normally by detecting a square wave output from the single chip microcomputer, and outputting a third high level signal when the single chip microcomputer works normally;processing 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; anddetermining 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. 2. The detecting method according to claim 1, further comprising outputting an alarm when the self-diagnosis output signal is a low level signal, which means that at least one of the first detecting coil, the second detecting coil, the signal processor and the single chip microcomputer work abnormally. 3. The detecting method according to claim 1, wherein the fuel ball sensor comprises:a housing;a pair of semi-ring frames disposed over the pipeline fitted with each other;an aviation plug or a feed-through filter connected with an output terminal of the first detecting coil and the second detecting coil; andan electromagnetic sealing gasket;wherein the first detecting coil and the second detecting coil respectively comprise a pair of semi-ring coils winding around the pair of semi-ring frames, and the electromagnetic sealing gasket fills in a gap between the semi-ring coils and contacts with the housing. 4. The detecting method according to claim 1, wherein determining whether the fuel ball passes the pipeline according to U0 comprises:determining whether the fuel ball waveform signal U0 is complete;determining whether the fuel ball waveform signal U0 is continuous;determining whether the fuel ball waveform signal U0 is symmetrical; anddetermining the fuel ball passes the pipeline when the fuel ball waveform signal U0 is complete, continuous and symmetrical. 5. The detecting method according to claim 4, wherein detecting whether the fuel ball waveform signal U0 is complete comprises:processing the fuel ball waveform signal U0 by dual threshold comparison to generate adjacent pulses,determining whether the adjacent pulses comprise a peak pulse UP1 and a valley pulse UP2;if yes, determining the fuel ball waveform signal U0 is complete; andif no, determining the fuel ball waveform signal U0 is incomplete. 6. The detecting method according to claim 5, wherein determining whether the fuel ball waveform signal U0 is continuous comprises:determining whether a time difference between a falling edge of the peak pulse UP1 and a rising edge of the valley pulse UP2 of the fuel ball waveform signal U0 adjacent to each other is less than a peak pulse width or a valley pulse width;if yes, determining the fuel ball waveform signal U0 is continuous; andif no, determining the fuel ball waveform signal U0 is discontinuous,wherein the peak pulse width is determined by a peak amplitude threshold UTh1 of the fuel ball waveform signal U0 and the valley pulse width is determined by a valley amplitude threshold UTh2 of the fuel ball waveform signal U0, in which UTh1=(a base value of U0 without the fuel ball+a peak value of U0 with the fuel ball)/2, UTh2=(the base value of U0 without the fuel ball+a valley value of U0 with the fuel ball)/2, in which the base value of U0 without the fuel ball is a preset value. 7. The detecting method according to claim 5, wherein determining whether the fuel ball waveform signal U0 is symmetrical comprises:determining whether waveform widths of the peak pulse UP1 and the valley pulse UP2 of U0 are similar to each other;if yes, determining the fuel ball waveform signal U0 is symmetrical; andif no, determining the fuel ball waveform signal U0 is dissymmetrical. 8. 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; andan 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; andan 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. 9. The detecting system according to claim 8, wherein the outputting module is further configured to output an alarm when the self-diagnosis output signal is a low level signal, which means that at least one of the first detecting coil, the second detecting coil, the signal processor and the single chip microcomputer work abnormally. 10. The detecting system according to claim 8, wherein the fuel ball sensor comprises:a housing;a pair of semi-ring frames disposed over the pipeline fitted with each other;an aviation plug or a feed-through filter connected with an output terminal of the first detecting coil and the second detecting coil; andan electromagnetic sealing gasket;wherein the first detecting coil and the second detecting coil respectively comprise a pair of semi-ring coils winding around the pair of semi-ring frames, and the electromagnetic sealing gasket fills in a gap between the semi-ring coils and contacts with the housing. 11. The detecting system according to claim 8, wherein the single chip microcomputer comprises:a first determining module configured to determine whether the fuel ball waveform signal U0 is complete;a second determining module configured to determine whether the fuel ball waveform signal U0 is continuous;a third determining module configured to determine whether the fuel ball waveform signal U0 is symmetrical. 12. The detecting system according to claim 11, wherein the first determining module is configured to:process the fuel ball waveform signal U0 by dual threshold comparison to generate adjacent pulses,determine whether the adjacent pulses comprise a peak pulse UP1 and a valley pulse UP2;if yes, determine the fuel ball waveform signal U0 is complete; andif no, determine the fuel ball waveform signal U0 is incomplete. 13. The detecting system according to claim 12, wherein the second determining module is configured to:determine whether a time difference between a falling edge of the peak pulse UP1 and a rising edge of the valley pulse UP2 of the fuel ball waveform signal U0 adjacent to each other is less than a peak pulse width or a valley pulse width;if yes, determine the fuel ball waveform signal U0 is continuous; andif no, determine the fuel ball waveform signal U0 is discontinuous,wherein the peak pulse width is determined by a peak amplitude threshold UTh1 of the fuel ball waveform signal U0 and the valley pulse width is determined by a valley amplitude threshold UTh2 of the fuel ball waveform signal U0, in which UTh1=(a base value of U0 without the fuel ball+a peak value of U0 with the fuel ball)/2, UTh2=(the base value of U0 without the fuel ball+a valley value of U0 with the fuel ball)/2, in which the base value of U0 without the fuel ball is a preset value. 14. The detecting system according to claim 12, wherein the third determining module is configured to:determine whether waveform widths of the peak pulse UP1 and the valley pulse UP2 of U0 are similar to each other;if yes, determine the fuel ball waveform signal U0 is symmetrical; andif no, determine the fuel ball waveform signal U0 is dissymmetrical. 15. The detecting system according to claim 8, wherein the resonance bridge detecting circuit comprises:a first bridge arm consisting of a first resistor and having a terminal connected with an output terminal of the exciting module to receive the exciting signal;a second bridge arm consisting of a second resistor and having a terminal connected with the output terminal of the exciting module to receive the exciting signal;a third bridge arm consisting of the first detecting coil, a first capacitor and a potentiometer connected in parallel with each other, wherein a first terminal of the third bridge arm is grounded and a second terminal of the third bridge arm is configured to output the first voltage signal U1;a fourth bridge arm consisting of the second detecting coil, a second capacitor and a third resistor connected in parallel with each other, wherein a first terminal of the fourth bridge is grounded and a second terminal of the fourth bridge arm is configured to output the second voltage signal U2. 16. The detecting system according to claim 8, wherein the detecting system has an isolated electromagnetic shielding structure.