主权项 |
1. A magnetic excitation circuit used as a circuit for providing a magnetic excitation electric current based on a magnetic excitation power supply voltage to a magnetic excitation coil of an electromagnetic flow meter, wherein the magnetic excitation electric current is switched to positive polarity/negative polarity with each positive interval/negative interval that are repeated with a specific period, where, at the times of the beginnings of these positive interval and negative interval the magnetic excitation power supply voltage is switched to a high voltage during a high-voltage interval, and after a specific time interval has elapsed after the starting time, the magnetic excitation power supply voltage is switched to a low voltage over a low-voltage interval, the magnetic excitation circuit comprising:
first and fourth switching elements that provide a magnetic excitation electric current that is switched to a positive polarity through turning ON during the positive interval and turning OFF during the negative interval, wherein a first delaying capactive element, which delays the first switching element turning ON, is connected between a control terminal and an output terminal of the first switching element; second and third switching elements that provide a magnetic excitation electric current that is switched to a negative polarity through turning OFF during the positive interval and turning ON during the negative interval, wherein a second delaying capacitive element, which delays the third switching element turning ON, is connected between a control terminal and an output terminal of the third switching element; a constant current circuit that controls the magnetic excitation electric current to a specific value; and voltage storing circuits, which store and output a driving voltage that is charged by a common driving voltage, connected individually between the respective controlling terminals and output terminals of the first through fourth switching elements to enable operation by a driving voltage that is outputted from the respective voltage storing circuits when the first through fourth switching elements are turned ON with the positive interval/negative interval. |