| 摘要 |
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.
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