A more sophisticated solution to this problem uses a pulsed excitation power source for the
flowtube coils. This is called DC excitation by magnetic flowmeter manufacturers, which is a bit
misleading because these “DC” excitation signals often reverse polarity, appearing more like an AC
square wave on an oscilloscope display. The motional EMF for one of these flowmeters will exhibit
the same waveshape, with amplitude once again being the indicator of volumetric flow rate. The
sensor electronics can more easily reject any AC noise voltage because the frequency and waveshape
of the noise (60 Hz, sinusoidal) will not match that of the flow-induced motional EMF signal.
The most significant disadvantage of pulsed-DC magnetic flowmeters is slower response time to
changing flow rates. In an effort to achieve a “best-of-both-worlds” result, some magnetic flowmeter
manufacturers produce dual-frequency flowmeters which energize their flowtube coils with two mixed
frequencies: one below 60 Hz and one above 60 Hz. The resulting voltage signal intercepted by the
electrodes is demodulated and interpreted as a flow rate