| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a thermal flowmeter which can reduce fluctuations in a sensor output in an intermediate flow range by completing output adjustment in one operation at each of two flow points (a virtual zero point and a span point). <P>SOLUTION: An amplifier circuit 30 comprises a virtual zero-point adjustment circuit 31 which includes a differential amplifier circuit 35 for amplifying a voltage in accordance with the difference between a reference voltage V1 and an output voltage V2 from a constant temperature difference circuit 23 and a variable-reference-voltage circuit 36 for varying the reference voltage V1 and performs virtual zero-point adjustment by a trimmer T1, a span-point adjustment circuit 32 which is configured as a noninverting amplifier circuit for amplifying an output voltage Vz from the differential amplifier circuit 35 with a predetermined amplification factor, includes a variable-amplification-factor trimmer T2, and performs span-point adjustment by adjusting the trimmer T2, and a voltage setting circuit 33 for setting each ground level of an operational amplifier OP1 and an operational amplifier OP2 to be a sensor output voltage value at the virtual zero point. <P>COPYRIGHT: (C)2008,JPO&INPIT</p> |
