| 摘要 |
PROBLEM TO BE SOLVED: To prevent erroneous measurement caused by an electric power source frequency noise intruding when no fluid flows. SOLUTION: A vortex detection sensor 1 has a first piezoelectric element 11 and a second piezoelectric element 12 outputting reverse polarities of charges in response to a vortex force. Outputs from the first piezoelectric element 11 and the second piezoelectric element 12 are converted into voltages by respective corresponding charge-voltage conversion circuits 21, 22, to be thereafter brought into a differential signal by a differential circuit 3, and it is input into a vortex frequency measuring circuit 5 via a filter circuit 4. Outputs from first and second charge-voltage conversion circuits 21, 22 are also input into respective corresponding switching circuits 61, 62 to be converted into pulse signals. A determination circuit 7 determines whether outputs from the switching circuits 61, 62 have reverse polarities or not, determines the outputs from the first piezoelectric element 11 and the second piezoelectric element 12 as ones not resulting from an alternating force of a vortex but resulting from the noise, when having the reverse polarities, and makes an output of the vortex frequency measuring circuit 5 not output by a switch 8. COPYRIGHT: (C)2009,JPO&INPIT
|
