Method and apparatus for testing electromagnetic flowmeters
First Claim
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1. A method of in situ testing of an electromagnetic flowmeter having a sensor coil circuit comprising a coil having coil properties, the method comprising:
- measuring at least two electrical parameters of the sensor coil circuit which enable detection of changes in the coil properties, comparing the measured parameters to stored parameters of the flowmeter, and determining whether the calibration of the flowmeter is accurate based on the results of the comparison so that the flowmeter is tested in situ.
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Abstract
An electromagnetic flowmeter is tested and calibrated in situ by measuring the impedance of the drive coil, and the isolation to ground impedance of the coil and of the flowmeter sensor electrodes. Testing is effected by portable field equipment or by a built-in test equipment facility with the flowmeter transmitter.
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Citations
22 Claims
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1. A method of in situ testing of an electromagnetic flowmeter having a sensor coil circuit comprising a coil having coil properties, the method comprising:
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measuring at least two electrical parameters of the sensor coil circuit which enable detection of changes in the coil properties, comparing the measured parameters to stored parameters of the flowmeter, and determining whether the calibration of the flowmeter is accurate based on the results of the comparison so that the flowmeter is tested in situ. - View Dependent Claims (2, 3, 4, 5, 6, 7)
the isolation-to-ground impedance of the sensor coil circuit; the isolation-to-ground impedance of the sensor electrode of the flowmeter; and
an eddy current resistance or loss component of the flowmeter.
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7. The method according to claim 1, wherein at least one of the electrical parameters includes measuring an exponentially changing variable selected from the group consisting of:
- a voltage across a coil, a current through a coil, a variable indicative of said voltage of current; and
determining a time constant from the exponentially changing variable.
- a voltage across a coil, a current through a coil, a variable indicative of said voltage of current; and
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8. A method of in situ testing of an electromagnetic flowmeter by obtaining electrical parameters thereof comprising
determining the ohmic resistance of an energizing coil thereof, measuring an exponentially-changing current in the coil or a variable related thereto, deriving a time constant therefrom, determining the inductance of the coil from the time constant and the ohmic resistance, and determining the accuracy of calibration of the flowmeter in situ using the foregoing measurements of the resistance and inductance of the coil.
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13. A method of in situ testing a flowmeter comprising measuring an exponentially changing current in an energizing coil of the flowmeter at two known time intervals from a datum and deriving from said measurements and time intervals an eddy current resistance of the flowmeter so that the flowmeter is tested in situ.
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14. An electromagnetic flowmeter testing apparatus wherein electrical parameters of the flowmeter are obtained comprising
means for determining the ohmic resistance of an energizing coil of the flowmeter, means for providing an exponentially-changing current in the coil, means for measuring said exponentially-changing current, means for deriving a time constant from the exponentially changing current, means for determining the inductance of the coil from the time constant and the ohmic resistance, and means for testing the accuracy of the calibration of the flowmeter in situ using the foregoing measurements of the resistance and inductance of the coil.
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15. A method of testing an electromagnetic flowmeter comprising
applying to an electrically-responsive component thereof an AC test signal of a frequency equal to that of a drive signal applied to an energizing coil of the flowmeter during normal operation thereof, said drive signal producing in a circuit of the flowmeter a response characteristic of an impedance of said electronically responsive component, and measuring said response characteristic by means of a sensing means of the flowmeter which during normal operation senses a signal characteristic of fluid flow through the flowmeter.
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19. An electromagnetic flowmeter testing apparatus comprising
means for applying to an electrically responsive component thereof an AC test signal of a frequency equal to that of a drive signal applied to an energizing coil of the flowmeter during normal operation thereof, so as to produce in a circuit of the flowmeter a response characteristic of an impedance of said electrically responsive component, and means for supplying said response characteristic to a sensing means of the flowmeter which during normal operation sense a signal characteristic of fluid flow through the flowmeter so that the sensing means measures said response characteristic.
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21. Apparatus for testing an electromagnetic flowmeter having a sensor coil circuit, the apparatus for testing comprising
means for measuring at least two electrical parameters of the sensor coil circuit, means storing predetermined values for said at least two electrical parameters, means for comparing the stored predetermined values for the at least two electrical parameters to the measured parameters, and means for outputting an indication of whether the flowmeter is within calibration based on the results of the comparison.
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22. A method of in situ testing of an electromagnetic flowmeter comprising
determining the ohmic resistance of an energizing coil thereof, measuring an exponentially-changing current in the coil or a variable related thereto, deriving a time constant therefrom, determining the inductance of the coil from the time constant and the ohmic resistance so that the flowmeter is tested in situ, repeating the measurement of the exponentially-changing current later in time than the first measurement, and employing said current measurements and the times thereof either to derive an eddy current resistance of the flowmeter, or to correct the determined value of the coil inductance for the effects of said eddy current resistance.
Specification