ELECTRO-MAGNETIC FLOW METER

摘要

PURPOSE:To increase the stability of the zero point and the response by selecting exciting current to a signal generator among three steady values and superposing in the same direction and calculating the noise components in the voltages induced between the electrodes when the signal becomes one of the three steady values. CONSTITUTION:Currents Ia-Ic from the constant current sources 11a-11c of an exciting circuit 1 are changed over by means of switches 12a-12c and given to the exciting coil 21 of an oscillator 2. The voltage induced between electrodes 23a and 23b is given to a signal processing circuits 3 and also to a calculation circuit 33 via an A/C current amplifier and sample holding circuit 32a and 32b. A pulse generator 34 is synchronized with the commercial A/C power and control switches 12a-12c and Sa and Sb. With this arrangement the circuit 33 eliminates noise components that are included in the exciting voltage ea and the offset component due to the D/C voltage and the circuit. Accordingly the voltage Vo that is related only to the signal component that is proportional to the flow rate of a liquid flowing in the pipe 22 can be obtained.