Abstract
A capacitance instrument is described, which is capable of detecting and measuring the amount of undissolved gas in either oil or water flowing in a pipe. Experimental results are presented relating meter output to gas concentration at known water velocities. Sensing electrodes are formed into an insulated section of the conveyor and form a capacitor in which the dielectric consists of a section of the following medium. This capacitor is connected in parallel with an inductor to form a parallel tuned oscillator circuit. The frequency of oscillation varies with the concentration of the second component. The second component is not uniformly distributed throughout the water but may be visualised as an average concentration with superimposed fluctuations. These fluctuations arise due to the random distribution of the phases and the turbulence of the flow. They are termed flow noise, and the resultant changes in capacitance cause corresponding changes in oscillator frequency. The change in frequency is detected by a frequency demodulator which produces a fluctuating voltage. The rms value of the fluctuations varies as the concentration of the second component.
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