| 摘要 |
PURPOSE:To change exciting frequency automatically in accordance with the oscillation of a flow rate signal and to secure stable operation by changing the exciting frequency of an oscillator on the basis of a decided result when the flow rate signal value exceeds a boundary value. CONSTITUTION:A switching control circuit 5 is controlled by the timing specified by an exciting current control program written in an ROM of a memory to turn switches SW1-1-SW1-4, generates exciting current If and excites the oscillator 1 at a three-state condition. Under said condition, comparison voltage Vr is generated in a resistor (r), and when fluid is made to flow into a measuring conduit 2, a flow rate signal having a similar waveform to the exciting current is obtained and stored in an RAM of the memory 9 through an A/D converter. A CPU8 calculates the average value of preceding sampling values, sets a boundary value in a range having prescribed upper and lower width for the average value, compares the new flow rate signal value with the boundary value to judge the degree of the oscillation of the flow rate signal, and on the basis of the judged result, changes the exciting frequency of the oscillator 1. |
