| 摘要 |
<p>PURPOSE: To improve the off-set and drift characteristic and stabilize the sensor output by providing a drive stopping means for correcting a power supplied to a heating element, a temperature difference detecting bridge, and an adjusting means for adjusting the output of the bridge. CONSTITUTION: A heating element drive part 13 is composed of a heating element drive circuit 10 for driving a heating element Rh, ad a switch SW1 as a drive stopping means 14. The switch SW1 is turned off while switches SW1, SW2 are turned so as to adjust a temperature difference detecting bridge circuit 14 is adjusted, a transmission path between the circuit 14 and a differential amplifier 17 and feed-back paths for a bridge circuit adjusting circuit 19 and an error detecting amplifier 18 establish a closed control loop system. The circuit 19 delivers a control voltage Vb to a MOS transistor 16a in the circuit 14, and balance control is continued until the output of the amplifier 17 becomes a reference voltage. Then, the switches SW2, SW3 in the bridge adjusting circuit 15 are turned off while the switch SW1 is turned on, and accordingly, a power is fed to the heating element Rh so as to measure a flow rate.</p> |
