JPS6412226A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To prevent the generation of induction harmful to an instrument, by a method wherein an excitation current is detected through a control switch between a bridge and a DC power source and a control element is controlled by a deviation from a reference voltage to turn the current to a fixed current value set by the reference voltage. CONSTITUTION:Switch SW1-4 are opened or closed to obtain an excitation current If. The current If increases at the rise thereof depending on a time constant of an exciting coil L2 and an error amplifier Q3 controls an FET transistors Q2. At the fall of the current, an excitation voltage Ve is controlled so as to equal an input voltage Vi. A voltage to be applied between the drain and source of the FETQ2 is detected with a voltage control section 11 and compared with a reference voltage E1 by a comparator Q1. To lower increase in a power loss, a voltage to be applied to the excitation coil only at the rise or fall of the excitation current is made equal to the voltage Vi, thereby preventing an instrument from making harmful induction.