Method for operating and/or reviewing a magneto-inductive flow meter

Abstract

A flow meter includes a measuring tube for conveying a fluid to be measured and a magnetic field system, which has at least one field coil, through which an exciter current (I) flows, at least at times, for producing a magnetic field passing through the fluid at least partly perpendicularly to a stream direction. In the method, the voltage (U) instantaneously driving the exciter current (I) is changed at a second point in time, t, from the second voltage level, U, to a third voltage level, U, especially to a third voltage level which is constant or controlled to be constant, in order to achieve a sinking of the electrical current strength of the exciter current (I) instantaneously flowing in the at least one field coil from the maximum current value, I, to an electrical current end value, I, especially a constant end value, predetermined for the exciter current (I). In such case, the third voltage level, U, is chosen smaller than the second voltage level, U. For determining a third point in time, t, which corresponds to the reaching of the electrical current end value, I, the exciter current Iis registered, at least at times. Based on this, a first time constant, T, for the magnetic field system is determined, which corresponds to a time span, t−t, lying between the second point in time, t, and the third point in time, t, and/or a second time constant, T+T, for the magnetic field system, which corresponds to a time span, t−t, lying between the first point in time, t, and the third point in time, t. For determining a diagnosis value representing an instantaneous operating state of the flow meter, the determined first time constant, T, is then compared with a predetermined first reference value, T, and/or the determined second time constant, T+T, is compared with a predetermined second reference value, T.