| 摘要 |
<P>PROBLEM TO BE SOLVED: To accurately detect whether a foreign substance is adhered to an electrode by a simple configuration. <P>SOLUTION: An analog flow rate signal (flow rate signal component + noise component) from an AC amplifier circuit 22 is converted into a digital signal by a first A/D conversion part 26. The digital signal is sampled by adopting one period e.g. of excitation frequency fex as a predetermined period and a value obtained by integrating the absolute values of all frequency components of the digital signal sampled in the predetermined period is set as a first integrated value X. A value obtained by integrating the absolute values of frequency components not less than a cut-off frequency fc (e.g. eight times the fex) out of the frequency components of the digital signal sampled in the predetermined period is set as a second integrated value Y. A ratio (Y/X) of the second integrated value Y to the first integrated value X is calculated as a high frequency ratio HR (adhesion noise evaluation value). When the high frequency ratio HR exceeds a diagnosis threshold SP<SB POS="POST">HR</SB>, it is determined that a foreign substance is adhered to an electrode. <P>COPYRIGHT: (C)2012,JPO&INPIT |
