an electromagnetic flow meter has a flow rate detector and a pulse width modulating circuit . the detector includes an exciting coil . the coil is excited by a square wave exciting current , thus inducing a voltage in a fluid . the voltage is picked up and used as a flow rate signal . the pulse width modulating circuit amplifies the flow rate signal , and also inverts and then amplifies the signal , thus providing an amplified flow rate signal and an inverted , amplified flow rate signal . the circuit further samples one of these signals , thereby generating a pulse signal whose width is proportional to the flow rate signal . the flow meter further comprises a timing control circuit . this circuit generates a first control signal frequency of either 50 hz or 60 hz divided by an even number and a second control signal . the first control signal controls the elements of the flow rate detector and pulse width modulation circuit . the second control signal controls the pulse width modulation circuit in such a manner that the circuit samples said signal repeatedly , each time for a predetermined period equal to the reciprocal of the other of 50 hz or 60 hz .