| 摘要 |
PURPOSE:To have stable sensing in a device to detect the condition of objects electromagnetically etc., regardless of the type of the object and its environments, by controlling the timing to compare the sensed signals with the reference signal which has undergone correction. CONSTITUTION:Ultra-sonic signals received by a receiver 15 are converted into electrical signals by a piezo transducer PET1, placed into a DC converter 19 through an amplifier 17, half-wave rectified, held with its peak value, and put into the comparator 27 and reference value memory 21. This memory 21 makes impedance conversion of these signals and charges a capacitor C5 with them, forms the discharge time constant by resistances R11, R12, and divides so that they will become the threshold voltage in the comparator 27. When a transcript paper passes the ultra-sonic receiver and transmitter, the gain will drop by min. 12dB in the amount of signal reception, so that the level lowered by 6dB from the terminal voltage of the capacitor C5 after being divided will become the threshold value and DELTAVH1 and DELTAVL1 are relatively corrected, and further a stabilized sensing is obtained even though the DELTAVH2 and DELTAVL2 have changed by 3dB with respect to VL.VH. |
