| 摘要 |
PURPOSE:To discriminate whether the internal pressure in an airtight container is normal or not precisely by exciting a metallic lid forcibly by electromagnetic induction, and finding and comparing its natural center frequency with the variable of a set frequency. CONSTITUTION:Current pulses are applied to the coil in a striking body 2 to excite the lid of the can forcibly, and its oscillation tone is detected by a microphone 4 and inputted to a group 6 of >=5 narrow-band filters which have >=5 selectivity and >=18db/ocT attenuation slope through an amplifier 5. A signal passed through each band-pass filter is rectified by a group 7 of rectifying circuits on full-wave basis and inputted to a group of a group 8 of integration holding circuits, where the output is held for a specific time. Then, integral output of the integration holding circuit is switched at a high speed by a signal switching circuit 9 to send a maximum value to a detecting and subtracting circuit 12, which detects a band having the maximum value among respective band outputs to calculate the difference between outputs of both adjacent bands. A set constant is added to this arithmetic output to obtain the variable of the natural oscillation center frequency, which is compared with a set value by a comparing circuit 13. |
