Patent ID: 8590361

Claim:
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.