Passenger detection system and detection method

• US 6,960,841 B2
• Filed: 02/19/2003
• Issued: 11/01/2005
• Est. Priority Date: 09/13/1999
• Status: Expired due to Fees

• Current Assignee: Honda Elesys Co., Ltd. (Nidec Corporation)
• Original Assignee: Honda Elesys Co., Ltd. (Nidec Corporation)
• Inventors: Saitou, Takashi, Oka, Yoshitaka, Jinno, Kazunori, Ofuji, Masahiro
• Primary Examiner(s): DeBeradinis, Robert L.
• Application Number:
  US10/368,036
• Publication Number:
  US 20030151240A1
• Time in Patent Office: 986 Days
• Field of Search: 307/10.1, 340/370.37, 340/667, 324/663, 180/273
• US Class Current: 307/10.1
• CPC Class Codes: B60R 21/01532 using electric or capacitive field sensors
• CPC Class Codes: B60R 21/0154 in combination with seat heating
• CPC Class Codes: B60R 21/33 Arrangements for non-electric triggering of inflation electrical circuits for triggering safety arrangements B60R21/01

Abstract

A passenger detection system is presented so that the master control circuit in the system instructs the passenger airbag control circuit controlling the operation of the airbag designated for the passenger seat to be in the deployable state or not-deployable state, depending on the seating conditions of a passenger sitting on the passenger seat, for example whether the passenger is an adult or a child. The passenger detection system is operated by a plurality of antenna electrodes disposed on the passenger seat; an electric field generation device for generating an electric field around an antenna electrode; a switching circuit for connecting the electric field generation device to the various antenna electrodes; an information detection circuit for detecting information related to a current flowing in a particular antenna electrode selected by the switching circuit; a master control circuit for receiving signal data output from the information detection circuit, and judging passenger seating conditions according to the signal data; and an airbag apparatus for controlling the operation of an airbag designated for the driver seat and an airbag designated for the passenger seat.

Claims

1. A passenger detection method comprising the steps of:

disposing a plurality of antenna electrodes separately on a seat;

selecting a particular antenna electrode from said plurality of antenna electrodes;

generating a weak electric field on said particular antenna electrode;

detecting information related to a current flowing in said particular antenna electrode resulting from applying said weak electric field; and

judging passenger seating conditions according to signal data related to said information.

2. A passenger detection method comprising the steps of:

disposing a plurality of antenna electrodes separately on a seat;

selecting a particular antenna electrode from said plurality of antenna electrodes;

generating a weak electric field on said particular antenna electrode;

detecting information related to a current flowing in said particular antenna electrode resulting from applying said particular weak electric field;

evaluating passenger seating conditions according to signal data related to said information and producing a judgment;

sending said judgment to an airbag apparatus so as to place an airbag of said airbag apparatus either in the deployable state or not-deployable state.

3. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

an amplitude control circuit for maintaining an amplitude of forward signals substantially constant;

a switching circuit for selecting a particular antenna electrode from said plurality of antenna electrodes and providing an electrical connection to said electric field generation device;

an information detection circuit for generating a particular weak electric field around said particular antenna electrode, and obtaining information related to a current flowing in said particular antenna electrode resulting from applying said particular weak electric field; and

a control circuit for receiving signal data from said information detection circuit and judging passenger seating conditions on said seat according to said signal data.

5. A passenger detection system according to one of claim 3 or 4, wherein said plurality of antenna electrodes are disposed on said sitting section and/or said backrest section.

6. A passenger detection system according to one of claim 3 or 4, wherein said amplitude control circuit includes, at least, an amplitude varying circuit for varying a voltage amplitude of forward signals and an amplitude detection circuit for detecting said voltage amplitude and controlling said voltage varying circuit so as to maintain said voltage amplitude substantially constant, according to output signals from said amplitude detection circuit.

4. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

an amplitude control circuit for maintaining an amplitude of forward signals substantially constant;

a switching circuit for selecting a particular antenna electrode from said plurality of antenna electrodes and providing an electrical connection to said electric field generation device;

an information detection circuit for generating a particular weak electric field around said particular antenna electrode, and obtaining information related to a current flowing in said particular antenna electrode resulting from applying said particular weak electric field;

a control circuit for receiving signal data from said information detection circuit and judging passenger seating conditions on said seat according to said signal data; and

an airbag apparatus for deploying, upon collision, an airbag designated for said seat;

wherein said airbag apparatus is programmed by said control circuit to be either in the deployable state or not-deployable state according to judging data generated by said control circuit.

7. A passenger detection method comprising the steps of:

disposing a plurality of antenna electrodes separately on a seat;

selecting a particular antenna electrode from said plurality of antenna electrodes;

generating a weak electric field on said particular antenna electrode by impressing field signals, whose voltage amplitude is controlled substantially constant, on said particular antenna electrode;

detecting information related to a current flowing in said particular antenna electrode resulting from applying said particular weak electric field; and

judging passenger seating conditions according to signal data related to said information.

8. A passenger detection method comprising the steps of:

disposing a plurality of antenna electrodes separately on a seat;

selecting a particular antenna electrode from said plurality of antenna electrodes;

generating a weak electric field on said particular antenna electrode by impressing field signals, whose voltage amplitude is controlled substantially constant, on said particular antenna electrode;

detecting information related to a current flowing in said particular antenna electrode resulting from applying said particular weak electric field;

evaluating passenger seating conditions according to signal data related to said information and producing a judgment; and

sending said judgment to an airbag apparatus so as to place an airbag of said airbag apparatus either in the deployable state or not-deployable state.

9. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit for selecting a particular antenna electrode from said plurality of antenna electrodes and providing an electrical connection to said electric field generation device;

an information detection circuit for generating a particular weak electric field around said particular antenna electrode, and obtaining information related to a current flowing in said particular antenna electrode resulting from applying said particular weak electric field; and

a control circuit for receiving signal data from said information detection circuit and judging passenger seating conditions on said seat according to said signal data;

wherein control circuit includes;

memory means for storing initial data SDn as reference data, obtained in a reference state including a vacant seat state by impressing a weak electric field on each antenna electrode and detecting a resulting current flow in each antenna electrode;

reception means for receiving detected data ADn, obtained when starting said passenger detection system by impressing a weak electric field on each antenna electrode and detecting a resulting current flow in each antenna electrode; and

judging means for computing a difference between said detected data ADn and said initial data SDn to produce essentially data DTn, where DTn=SDn−

ADn, and judging passenger seating conditions according to said essentially true data.

10. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit for selecting a particular antenna electrode from said plurality of antenna electrodes and providing an electrical connection to said electric field generation device;

an information detection circuit for generating a particular weak electric field around said particular antenna electrode, and obtaining information related to a current flowing in said particular antenna electrode resulting from applying said particular weak electric field;

a control circuit for receiving signal data from said information detection circuit and judging passenger seating conditions on said seat according to said signal data;

an airbag apparatus having a capability to select an operational state of an airbag designated for said seat; and

communication means for sending judgment data, based on a judgment derived by said control circuit, to said airbag apparatus;

wherein control circuit includes;

memory means for storing initial data SDn as reference data, obtained in a reference state including a vacant seat state by impressing a weak electric field on each antenna electrode and detecting a resulting current flow in each antenna electrode;

reception means for receiving detected data ADn, obtained when starting the passenger detection system, by impressing a weak electric field on each antenna electrode and detecting a resulting current flow in each antenna electrode; and

judging means for computing a difference between said detected data ADn and said initial data SDn to produce essentially true data DTn, where DTn=SDn−

ADn, and judging passenger seating conditions according to said essentially true data.

11. A passenger detection method for a passenger detection system to detect seating conditions of a passenger seated on a seat by generating an electric field successively in a plurality of antenna electrodes disposed on said seat, detecting information related to a current flow in each antenna electrode caused by respective impressed electric field and judging passenger seating conditions according to said information, wherein said method includes the steps of:

storing initial data SDn as reference data obtained in a reference state including a vacant seat state, produced by impressing a weak electric field on each antenna electrode and detecting a resulting current flow in each antenna electrode;

receiving detected data ADn, obtained after starting said passenger detection system, by impressing a weak electric field on each antenna electrode and detecting a resulting current flow in each antenna electrode;

computing a difference between said detected data ADn and said initial data SDn to produce essentially true data DTn, where DTn=SDn−

ADn; and

evaluating passenger seating conditions according to said essentially true data.

12. A passenger detection method for a passenger detection system to detect seating condition of a passenger seated on a seat by generating a weak electric field around each of a plurality of antenna electrodes disposed on said seat, detecting information related to a current flow in each antenna electrode caused by respective impressed electric field, judging seating conditions based on signal data related to said information, and sending said judgment to an air bag apparatus so as to place an airbag of said airbag apparatus either in the deployable state or not-deployable state, wherein said method includes the steps of:

initializing sensors so as to store initial data SDn as reference data obtained in a reference state including a vacant seat state, produced by impressing a weak electric field on each antenna electrode and detecting a resulting current flow in each antenna electrode; and

after starting said passenger detection system, receiving detected data ADn, produced by successively impressing a weak electric field on each antenna electrode and detecting a resulting current flow in each antenna electrode;

computing a difference between said detected data ADn and said initial data SDn to produce essentially true data DTn, where DTn=SDn−

ADn;

evaluating passenger seating conditions according to said true data;

sending resulting evaluation data to airbag apparatus using communication means; and

prior to placing said airbag apparatus in a selected operational state, performing an SRS process by exchanging evaluation data between a passenger detection circuitry and an airbag apparatus circuitry to examine whether or not there is abnormality in communication circuitry.

13. A passenger detection system having a plurality of antenna electrodes disposed separately on a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit for selecting a particular antenna electrode from said plurality of antenna electrodes and providing an electrical connection to said electric field generation device;

an information detection circuit for generating a particular weak electric field around said particular antenna electrode, and obtaining information related to a current flow resulting from said particular weak electric field;

a control circuit for receiving signal data from said information detection circuit and judging passenger seating conditions on said seat according to said signal data;

an airbag apparatus for enabling to deploy, upon collision, an airbag designated for said seat; and

communication means for sending a resulting judgment to said airbag apparatus, wherein resulting evaluation data are sent to airbag apparatus using communication means; and

prior to placing said airbag apparatus either in the deployable state or not-deployable state, checking system operation by exchanging evaluation data between a passenger detection circuitry and an airbag apparatus circuitry to examine whether or not there is abnormality in a communication circuitry between said passenger detection circuitry and said airbag apparatus circuitry.

14. A passenger detection method comprising the steps of:

generating a weak electric field successively around a plurality of antenna electrodes disposed on a seat;

detecting information related to a current flowing in successive antenna electrodes;

receiving signal data regarding said information;

evaluating passenger seating conditions according to received signal data and producing a judgment;

sending said judgment to an airbag apparatus; and

prior to placing an airbag of said airbag apparatus in a selected operational state;

checking system operation by exchanging SRS data between a passenger detection circuitry and an airbag apparatus circuitry to examine whether or not there is abnormality in a communication circuitry between said passenger detection circuitry and said airbag apparatus circuitry.

16. A passenger detection system according to one of claims 14 or 15, wherein a problem diagnostic step is added to an overall method of passenger detection.

15. A passenger detection method for a passenger detection system to detect passenger seating conditions on a seat by generating a weak electric field successively around a plurality of antenna electrodes disposed on a seat;

detecting information related to a current flowing in successive antenna electrodes;

judging passenger seating conditions according to signal data on said information; and

sending a resulting judgment to an airbag apparatus so as to place an airbag designated for said seat either in the deployable state or not-deployable state, wherein when said seat is vacant, generating a weak electric field successively on said plurality of antenna electrodes;

detecting information related to a current flowing in successive antenna electrode resulting from applying said weak electric field;

initializing sensors so as to store initial data SDn obtained, in a reference state including a vacant seat state, by generating a weak electric field successively on a plurality of antenna electrodes and detecting information related to a current flow caused by respective weak electric field; and

after starting said passenger detection system, receiving detected data ADn, produced by successively impressing an electric field on each antenna electrode and detecting a resulting current flow in each antenna electrode;

computing a difference between said detected data ADn and said initial data SDn to produce essentially true data DTn, where DTn=SDn−

ADn;

evaluating passenger seating conditions according to said essentially true data;

sending resulting evaluation data to airbag apparatus using communication means; and

prior to placing said airbag apparatus in a selected operational state, performing an SRS process by exchanging evaluation data between a passenger detection circuitry and an airbag apparatus circuitry to examine whether or not there is abnormality in a communication circuitry between said passenger detection circuitry and said airbag apparatus circuitry.

17. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a current detection circuit for applying said weak electric field to a particular antenna electrode and detecting a resulting current flowing in said particular antenna electrode; and

a control circuit for evaluating passenger sitting conditions according to signal data received from said current detection circuit;

wherein all antenna electrodes, excepting said particular antenna electrode selected for generating a weak electric field, are impressed with a direct current potential or earth potential.

18. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit having a plurality of switching devices for selecting a particular electrode and connecting said electric field generation device to said particular antenna electrode;

a current detection circuit for applying said weak electric field to said particular antenna electrode and detecting a resulting current flowing in said particular antenna electrode; and

a control circuit for evaluating passenger sitting conditions according to signal data received from said current detection circuit;

wherein all antenna electrodes, excepting said particular antenna electrode selected for generating a weak electric field, are impressed with a direct current potential or earth potential.

19. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a current detection circuit for applying said weak electric field to a particular antenna electrode and detecting a resulting current flowing in said particular antenna electrode; and

a control circuit for evaluating passenger sitting conditions according to signal data received from said current detection circuit;

wherein all antenna electrodes, excepting said particular antenna electrode selected for generating a weak electric field, are impressed with a direct current potential or earth potential, and evaluation data from said control circuit are sent to an airbag apparatus so as to place an airbag designated for said seat in the deployable state or not-deployable state.

20. A passenger detection method by generating a weak electric field selectively around a particular antenna electrode selected from a plurality of antenna electrodes disposed separately on a sitting section and/or backrest section of a seat;

applying a direct current potential or earth potential to all antenna electrodes excepting said particular antenna electrode; and

evaluating passenger seating conditions according to signal data of a perturbation current resulting from applying said weak electric field.

21. A passenger detection method by generating a weak electric field selectively around a particular antenna electrode selected from a plurality of antenna electrodes disposed separately on a sitting section and/or backrest section of a seat;

applying a direct current potential or earth potential to all antenna electrodes excepting said particular antenna electrode; and

evaluating passenger seating conditions according to signal data of a perturbation current resulting from applying said weak electric field to produce an evaluation result, and sending instruction data based on said evaluation result from said control circuit to an airbag apparatus so as to place an airbag designated for said seat in the deployable state or not-deployable state.

22. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit for selecting a particular electrode and connecting said electric field generation device to said particular antenna electrode;

an information detection circuit for applying said weak electric field to said particular antenna electrode and detecting information related to a current flowing in said particular antenna electrode resulting from applying said weak electric field; and

a control circuit for evaluating passenger sitting conditions according to signal data received from said information detection circuit;

wherein said electric field generation device outputs high frequency low voltage signals having a rectangular waveform.

24. A passenger detection system according to claim 22 or 23, wherein a plurality of antenna electrodes are disposed on a sitting section and/or a backrest section of a seat.

25. A passenger detection system according to claim 22 or 23, wherein electric field generation device generates high frequency low voltage signals of a rectangular waveform by switching a direct current voltage maintained at a positive constant voltage at a selected frequency.

26. A passenger detection system according to claim 22 or 23, wherein electric field generation device generates high frequency low voltage signals of a rectangular waveform by dividing a clock signal in a control circuit at a selected interval.

23. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a seat;

an electric field generation device for generating a weak electric field around an antenna electrode by outputting high frequency low voltage signals having a rectangular waveform;

a switching circuit for selecting a particular electrode and connecting said electric field generation device to said particular antenna electrode;

an information detection circuit for applying said weak electric field to said particular antenna electrode and detecting information related to a current flowing in said particular antenna electrode resulting from applying said weak electric field; and

a control circuit for evaluating passenger sitting conditions according to signal data received from said information detection circuit to produce an evaluation result, and sending instruction data based on said evaluation result from said control circuit to an airbag apparatus so as to place an airbag designated for said seat in the deployable state or not-deployable state.

27. A passenger detection method by generating a weak electric field selectively around a particular antenna electrode selected from a plurality of antenna electrodes disposed separately on a seat;

applying high frequency low voltage signals of a rectangular waveform on said particular antenna electrode; and

detecting information related to perturbation current flowing is said particular antenna electrode; and

evaluating passenger seating conditions according to signal data related to said information.

28. A passenger detection method by generating a weak electric field selectively around a particular antenna electrode selected from a plurality of antenna electrodes disposed separately on a seat;

applying high frequency low voltage signals of a rectangular waveform on said particular antenna electrode; and

detecting information related to a perturbation current flowing is said particular antenna electrode; and

evaluating passenger seating conditions according to signal data related to said information to produce an evaluation result, and sending instruction data based on said evaluation result from said control circuit to an airbag apparatus so as to place an airbag designated for said seat in the deployable state or not-deployable state.

29. A passenger detection system comprising:

an antenna electrode disposed on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around said antenna electrode;

an ac-dc conversion circuit for converting an alternating current line voltage in a forward line, related to a perturbation current flowing in said antenna electrode resulting from said weak electric field generated around said antenna electrode produced by connecting said antenna electrode to said electric field generation device, to a direct current voltage; and

a control circuit for judging passenger seating conditions according to evaluation data output from said conversion circuit.

35. A passenger detection system according to one of claims 29 to 34, wherein an RC time constant circuit is formed by capacitance components existing in a vicinity of an antenna electrode and a resistor connected in series to a forward circuitry including an electric field generation device.

36. A passenger detection system according to one of claims 29 to 34, wherein an impedance conversion circuit is provided between a forward circuitry for sending output signals from an electric field generation device and an ac-dc conversion device.

37. A passenger detection system according to claim 36, wherein said impedance conversion circuit is comprised by an operational amplifier having an amplification factor of 1.

38. A passenger detection system according to one of claims 29 to 34, wherein said control circuit is comprised, at least, by memory means for storing threshold value related to passenger seating conditions, means for receiving output signals from an ac-dc conversion circuit, and a judging section for judging passenger seating conditions by comparing threshold values with received signal data.

39. A passenger detection system according to one of claims 29 to 34, wherein said electric field generation device, said ac-dc conversion circuit, and said control circuit are housed in a common housing to form a control unit, which is incorporated in said seat.

40. A passenger detection system according to one of claims 29 to 34, wherein said electric field generation device, ac-dc conversion circuit, and said control circuit are housed in a common housing to form a control unit, and those constituting elements requiring an electric power source are supplied with power from an electric power source Vcc outputting a constant direct current voltage.

30. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit for selecting a particular electrode and connecting said electric field generation device to said particular antenna electrode;

an ac-dc conversion circuit for applying said weak electric field to said particular antenna electrode, and convening a resulting alternating current line voltage in a forward line related to a perturbation current flowing in said particular electrode to a direct current voltage; and

a control circuit for judging passenger seating conditions according to signal data output from said conversion circuit.

31. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit for selecting a particular electrode to serve as a sending electrode and selecting a pairing electrode serving a receiving electrode, and connecting said electric field generation device to said particular antenna electrode;

an ac-dc conversion circuit for generating a weak electric field between a resulting pair of antenna electrodes, and converting a resulting alternating current line voltage in a forward line related to a perturbation current flowing in said particular electrode to a direct current voltage; and

a control circuit for judging passenger seating conditions according to signal data output from said conversion circuit.

32. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit for selecting a particular electrode and connecting said electric field generation device to said particular antenna electrode;

an ac-dc conversion circuit for applying said weak electric field to said particular antenna electrode, and converting a resulting alternating current line voltage in a forward line related to a perturbation current flowing in said particular electrode to a direct current voltage; and

a control circuit for judging passenger seating conditions according to signal data output from said conversion circuit to produce an evaluation result, and sending instruction data based on said evaluation result from said control circuit to an airbag apparatus so as to place an airbag designated for said seat in the deployable state or not-deployable state.

33. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit for selecting a particular electrode and connecting said electric field generation device to said particular antenna electrode;

an ac-dc conversion circuit for applying said weak electric field to said particular antenna electrode, and converting a resulting alternating current line voltage in a forward line related to a perturbation current flowing in said particular electrode to a direct current voltage; and

a control circuit for judging passenger seating conditions according to signal data output from said conversion circuit.

34. A passenger detection system comprising:

a plurality of antenna electrodes disposed separately on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

a switching circuit for selecting a particular electrode and connecting said electric field generation device to said particular antenna electrode;

an ac-dc conversion circuit for applying said weak electric field to said particular antenna electrode, and converting a resulting alternating current line voltage in a forward line related to a perturbation current flowing in said particular electrode to a direct current voltage; and

a control circuit for judging passenger seating conditions according to signal data output from said conversion circuit to produce an evaluation result, and sending instruction data based on said evaluation result from said control circuit to an airbag apparatus so as to place an airbag designated for said seat in the deployable state or not-deployable state.

41. A passenger detection system comprising:

an antenna electrode disposed on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around said antenna electrode;

an antennae interface circuit including a detection circuit for detecting information related to a perturbation current flowing in said antenna electrode resulting from applying a power from said electric field generation device;

a correction interface circuit including a detection circuit for detecting information related to a perturbation current flowing in said antenna electrode resulting from applying a power from said electric field generation device; and

a control circuit for correcting signals output from said antennae interface circuit according to signal data output from said antennae interface circuit and said correction interface circuit;

wherein said antennae interface circuit and said correction interface circuit are configured similarly and said antennae interface circuit is connected to an antenna electrode and said correction interface circuit is not connected to an antenna electrode and is open-circuited.

43. A passenger detection system according to one of claim 41 or 42, wherein said antennae interface circuit is comprised of, at least:

an electric field generation device for generating a weak electric field around an antenna electrode;

an ac-dc conversion circuit for connecting an antenna electrode to said electric field generation device to generate a weak electric field, and converting ac voltage related to a perturbation current flowing in said antenna electrode, resulting from applying said weak electric field, to dc data.

44. A passenger detection system according to claim 43, wherein an RC time constant circuit is formed by capacitance components existing in a vicinity of an antenna electrode and a resistor connected in series to a forward circuitry including an electric field generation device.

45. A passenger detection system according to claim 43, wherein an impedance conversion circuit is provided between a forward circuitry for sending output signals from an electric field generation device and an ac-dc conversion device.

46. A passenger detection system according to claim 45, wherein said impedance conversion circuit is comprised by an operational amplifier having an amplification factor of 1.

47. A passenger detection system according to one of claim 41 or 42, wherein said control circuit is comprised of, at least:

memory means for storing signal data output from said correction interface circuit;

means for receiving signals output from said antennae interface circuit;

a correction section for compensating for drift according to correction data received;

an evaluation section for evaluating passenger seating conditions according to correction results output from said correction section.

48. A passenger detection system according to one of claim 41 or 42, wherein said antennae interface circuit and said correction interface circuit are comprised by, at least:

an electric field generation device;

a current detection device for detecting a perturbation current produced by application of power by said electric field generation device;

wherein said antennae interface circuit is connected to an electrode and said correction circuit is not connected to an antenna electrode and is open-circuited.

42. A passenger detection system comprising:

an antenna electrode disposed on a sitting section and/or a backrest section of a seat;

an electric field generation device for generating a weak electric field around an antenna electrode;

an antennae interface circuit including a detection circuit for detecting information related to a perturbation current flowing in an antenna electrode resulting from applying a power from said electric field generation device;

a correction interface circuit including a detection circuit for detecting information related to a perturbation current flowing in an antenna electrode resulting from applying a power from said electric field generation device;

a control circuit for correcting signals output from said antennae interface circuit according to signal data output from said antennae interface circuit and said correction interface circuit; and

an airbag apparatus that can be placed in a specific operational state according to judgment data generated by said control circuit;

wherein said antennae interface circuit and said correction interface circuit are configured similarly and said antennae interface circuit is connected to an antenna electrode and said correction interface circuit is not connected to an antenna electrode and is open-circuited.

49. A passenger detection system comprised by antenna electrodes disposed on a seat inside an automobile connected, using a shielding cable whose signal line is shielded by a shielding line, to a signal processing circuit for detecting passenger seating conditions by processing signal data related to a perturbation current flowing in an antenna electrode resulting from applying a weak electric field generated about said antenna electrode, wherein a buffer circuit, for maintaining signal levels of signal line and shield line at a same level, is connected between said signal line and said shield line.

50. A passenger detection system according to claim 49, wherein a plurality of antenna electrodes are disposed on said seat, and antenna electrodes and said signal processing circuit are wired using a plurality of shielding cables.

51. A passenger detection system according to claim 49, wherein a common buffer circuit is connected to each of said plurality of antenna electrodes and signal processing circuit through a respective switching element.