CAPACITIVELY COUPLED MAGNETIC FLOWMETER

摘要

A magnetic flowmeter of the capacitively-coupled type includes low-input impedance detection circuitry which responds to a flow induced current signal that is related to the voltage induced at the electrodes by the intersection of the flowing fluid and a time varying magnetic field. An on-line measure of the electrode capacitance that is non-interactive with the flow induced current signal is accomplished by creating a voltage difference between the process fluid and the electrodes which causes a capacitance-related current to flow from the electrodes proportional to the value of the electrode capacitance as well as the rate of change of the magnetic field. In one embodiment the primary element and the detection circuitry are referenced to a different potential than that of the process fluid and the adjacent piping of the flow system. Thus a direct, on-line measure of this capacitance can be attained in a manner that essentially eliminates stray leakage currents and that foregoes the needs for special shielding requirements such as localized, internal shields around the imbedded electrodes.