| 摘要 |
<p>PURPOSE:To perform detection with high accuracy by enhancing detection sensitivity by detecting the change of the heat conduction of a flow passage by a filament heated under a constant temp. and constant resistance condition. CONSTITUTION:An apparatus is equipped with the measuring filament arranged in a flow passage 2, a detection circuit 8 detecting the change of the resistance of the filament 1 and a heating control circuit 6 controlling a heating current on the basis of the output of the detection circuit 8 so that the filament shows constant resistance and constituted so as to obtain the measuring signal of the flow rate or fluid component of the flow passage corresponding to the control quantity of the heating control circuit 6. That is, the detection circuit 8 is constituted so that the non-equilibrium of a bridge 7 is detected by a comparator composed of a differential amplifier 9 and converted to DC by a synchronous rectifying circuit 10. The drift of the circuit is cancelled by synchronous rectification. A reference filament 21, a detection circuit 27 and a heating control circuit 26 of the same constitution are provided on a reference side and this reference apparatus is connected to the above mentioned apparatus on a measuring side by subtraction coupling to obtain a measuring signal. By this constitution, the residual error of the circuit is perfectly cancelled and highly accurate detection can be performed.</p> |
