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A flow sensing head for a magnetic flow sensor may be configured as an insertion probe having one or more flow passageways oriented perpendicular to the magnetic axis of an electromagnet. When a conductive liquid flows through the passageway a voltage is induced between two electrodes spaced out alo

A flow sensing head for a magnetic flow sensor may be configured as an insertion probe having one or more flow passageways oriented perpendicular to the magnetic axis of an electromagnet. When a conductive liquid flows through the passageway a voltage is induced between two electrodes spaced out along a line perpendicular to the passageway and to the axis of the electromagnet. A portion of the lead wires from the electrodes is fed through an axial throughhole in a conductive core of the electromagnet in order to electrostatically shield the wires from extraneous voltage sources. A preferred flow sensing head has two flow passageways, each with its own pair of electrodes. Signals from the two pairs of electrodes may be combined in a series-aiding arrangement, or in a parallel arrangement, or the signals from the two pairs of electrodes may be processed independently of each other.

대표청구항 ▼

A flow sensing head for a magnetic flow sensor may be configured as an insertion probe having one or more flow passageways oriented perpendicular to the magnetic axis of an electromagnet. When a conductive liquid flows through the passageway a voltage is induced between two electrodes spaced out alo

A flow sensing head for a magnetic flow sensor may be configured as an insertion probe having one or more flow passageways oriented perpendicular to the magnetic axis of an electromagnet. When a conductive liquid flows through the passageway a voltage is induced between two electrodes spaced out along a line perpendicular to the passageway and to the axis of the electromagnet. A portion of the lead wires from the electrodes is fed through an axial throughhole in a conductive core of the electromagnet in order to electrostatically shield the wires from extraneous voltage sources. A preferred flow sensing head has two flow passageways, each with its own pair of electrodes. Signals from the two pairs of electrodes may be combined in a series-aiding arrangement, or in a parallel arrangement, or the signals from the two pairs of electrodes may be processed independently of each other. value if said opening event is detected; and setting a first fault code indicating that said gross leak has been detected if said leak check timer has not exceeded said first predetermined threshold value and setting a second fault code indicating that said small leak has been detected if said leak check timer has not exceeded said second predetermined threshold value. 2. The method of claim 1 wherein said first threshold value corresponds to an amount of time required for a leak to be detected having a diameter of about 0.070 inches or greater. 3. The method of claim 2 wherein said first threshold value is dependent upon a level of fuel in a fuel tank of said automotive vehicle. 4. The method of claim 1 wherein said second threshold value corresponds to an amount of time required for a leak to be detected having a diameter of about 0.040 inches or greater. 5. The method of claim 4 wherein said second threshold value is dependent upon a level of fuel in a fuel tank of said automotive vehicle. 6. The method of claim 1 further comprising determining that a minimum inoperative time has elapsed prior to said step of sealing said evaporative emission control system. 7. The method of claim 1 further comprising determining that a set of operating conditions are met prior to said step of sealing said evaporative emission control system. 8. The method of claim 7 wherein said set of operating conditions further comprise that an ambient temperature is between a minimum and maximum ambient temperature. 9. The method of claim 7 wherein said set of operating conditions further comprise that a fuel level is between a minimum and maximum fuel level. 10. The method of claim 7 wherein said set of operating conditions further comprise that a battery voltage is between a minimum and maximum battery voltage. 11. The method of claim 7 wherein said st of operating conditions further comprise that an altitude is less than a maximum altitude. 12. The method of claim 1 wherein said step of purging said evaporative emission control system further comprises shutting a valve disposed along a first conduit extending between a canister of said evaporative emission control system and atmosphere and drawing a vacuum on said evaporative emission control system with a manifold of said automotive vehicle. 13. The method of claim 1 wherein said step of sealing said evaporative emission control system further comprises shutting a first valve disposed along a first conduit extending between a canister of said evaporative emission control system and atmosphere, and shutting a second valve disposed along a second conduit extending between a canister of said evaporative emission control system and a manifold of said automotive vehicle. 14. The method of claim 1 wherein said step of purging said evaporative emission control system is deemed complete upon the expiration of a purge timer. 15. The method of claim 1 further comprising opening a vacuum relief valve coupled to said evaporative emission control system if a pressure within said evaporative emission control system exceeds a given value. 16. The method of claim 1 further comprising opening a vacuum relief valve coupled to said evaporative emission control system if a pressure within said evaporative emission control system drops below a given value. 17. A method of detecting a small or gross leak in an evaporative emission control system of an automotive vehicle comprising: purging said evaporative emission control system; sealing said evaporative emission control system; monitoring a vacuum switch coupled to said evaporative emission control system for an opening event due to a loss of a natural vacuum created in said evaporative emission control system; determining if a leak check timer has exceeded a first or second predetermined threshold value if said opening event is detected; conducting an intrusive test of said evaporative emission control system if said leak check timer has not exceeded said