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The flow rate of a conducting liquid is generally measured by an electromagnetic flowmeter, which requires a magnetization coil and a set of sensing electrodes. However, the size and cost of the flow head of this flowmeter generally become very high due to the large size of the magnetizing coil and core material. In this paper, a novel low-cost bridge-type technique of flow measurement of a conducting liquid has been described. In this technique, the lumped-parameter impedances among four electrodes placed at a radial distance apart in a flow-sensing tube form a Wheatstone bridge network. Each of these impedances is a combination of electrode polarization impedances and other impedances. Since the electrode polarization impedances are functions of the flow rate of the conducting liquid and some other parameters, the polarization impedances between two electrodes placed in two locations along the flow path of the conducting liquid may be taken as a measure of the flow rate of the liquid, with the other parameters remaining constant. The nonlinearity of these impedance variations with the flow rate is minimized by the proposed bridge-circuit near-balanced condition. The bridge is excited by a stabilized sinusoidal oscillator and balanced at the no-flow condition of the liquid. The output of the bridge network is converted into a 1- to 5-V dc signal in a signal conditioner circuit. The design aspects, theoretical analysis, and calibration data are presented in this paper. The experimental characteristic of the flowmeter is found to follow the theoretical equation and has good repeatability over the entire operating zone.
Instrumentation and Measurement, IEEE Transactions on (Volume:58 , Issue: 8 )
Date of Publication: Aug. 2009