| 摘要 |
PURPOSE:To obtain a sufficient measuring sensitivity without a rise in hot wire temperature, by allowing the resistance of the hot wire to change and break the balance of a bridge circuit as a Karman's vortex passes so that a differential voltage output can be generated. CONSTITUTION:As the temperature of a hot wire 1 lowers with the passage of a Karman's vortex, the resistance value falls so much to break the balance of a bridge circuit 2 so that a differential voltage output Ve will appear. As a result, an amplified output Vo changes and the changed portion is inputted into a waveform shaping circuit 5. The change in the output Vo at this moment is based on an offset voltage Vc. With the change in the output Vo, a working voltage to be given to the circuit 2 changes and current of the hot wire 1 increases to raise the temperature thereof. Then, as the temperature of a fluid rises, the cooling degree of the ho wire 1 due to the Karman's vortex comes downs to reduce the output Ve of the circuit 2. So, a voltage Vc is altered with a voltage alternation circuit 8 to enhance the resonance intensity of the circuit. As a result, the output Vo changes greatly enough. In this manner, the output Vo varies as each Karman's vortex passes and the frequency of the change as enables the learning of the flow rate of the fluid. |
