Optimisation of a Voltage Measurement and Control Circuit for an Imaging Electromagnetic Flow Meter

This paper describes the optimisations conducted on an existing voltage measurement and control
circuit to allow its use in a novel imaging electromagnetic flow meter. This flow meter is a multielectrode device that can construct a velocity profile in both single and multiphase flow applications. Voltages are induced in the fluid flowing through the flow meter section due to the interaction of the fluid and the locally generated magnetic field. These voltages are detected by an array of electrodes and measured by a 7-channel system, based on the voltage measurement and control circuit. Each channel measures the potential difference between two electrodes in the flow cross section. The voltage measurement and control circuit comprises a very high amplification stage and an integral controller. The amplification stage is required to amplify the induced voltages of mV to V, suitable for analogue-to-digital conversion. The integral controller acts to eliminate the DC error component introduced in the amplification stage to prevent the circuit from exceeding its operational dynamic range limit. The existing voltage measurement and control circuit design has several drawbacks. The very high amplification stage occasionally causes the circuit to exceed its operational dynamic range.
In addition, the integral controller has a slow action response which results in a long settling time and offset error. These drawbacks were overcome in the optimised design - discussed in this paper.