Magnetic flow meters with automatic field maintenance
First Claim
1. An apparatus for automatically calibrating a magnetic flow meter comprising an electromagnet and at least one pair of sensing electrodes connected to an amplifier circuit operable to amplify electrode voltages by a selected amplification factor, the apparatus comprising:
- a single voltage reference source selectively connectable to an input of the amplifier circuit through a first voltage divider and to an output of the amplifier circuit through a second voltage divider, wherein a ratio of the voltage provided by the second voltage divider to the voltage provided by the first voltage divider is substantially equal to the selected amplification factor;
sampling circuitry operable to determine a magnitude of an error difference between a first output from the amplifier circuit at a first time when the single voltage reference source is connected and a second output from the amplifier circuit at a second time when the single voltage reference source is not connected; and
span control circuitry operable to change the selected amplification factor responsive to the magnitude of the error difference.
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Accused Products
Abstract
Zero and calibration drift errors in a magnetic flow meter can be detected and automatically corrected. A zero error can be detected by measuring an amplifier output when the meter'"'"'s electromagnet is inactive. Automatic calibration of the span can be done by adding a signal to a measured electrode voltage at an amplifier input, subtracting the expected amplified value of that signal at the output and adjusting the amplifier gain responsive to the difference in signal magnitude.
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Citations
8 Claims
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1. An apparatus for automatically calibrating a magnetic flow meter comprising an electromagnet and at least one pair of sensing electrodes connected to an amplifier circuit operable to amplify electrode voltages by a selected amplification factor, the apparatus comprising:
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a single voltage reference source selectively connectable to an input of the amplifier circuit through a first voltage divider and to an output of the amplifier circuit through a second voltage divider, wherein a ratio of the voltage provided by the second voltage divider to the voltage provided by the first voltage divider is substantially equal to the selected amplification factor; sampling circuitry operable to determine a magnitude of an error difference between a first output from the amplifier circuit at a first time when the single voltage reference source is connected and a second output from the amplifier circuit at a second time when the single voltage reference source is not connected; and span control circuitry operable to change the selected amplification factor responsive to the magnitude of the error difference. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification