| 摘要 |
PURPOSE: To obtain a device with less influence of stray capacitance for the output signal of an amplifier with a simple configuration so that the peak value of the output of an amplification circuit that changes according to the dielectric constant of an article passing between electrodes for forming a capacitor can be detected. CONSTITUTION: A continuous electrode 1 and an electrode assembly 2 with a number of detection electrodes 3 and a guard electrode 4 are arranged in parallel and one capacitor is formed by the electrodes 1 and 3. The electrode 3 is electrically connected to the inverted input of an operational amplifier 9 and the non-inverted input is connected to the ground potential. Then, an article (a blister packaged object containing a tablet) is passed between the electrodes 1 and 2. The capacitance between the electrodes 3 and 1 depends on the dielectric constant of the article located between them and changes depending on whether a tablet exists in an article 22 or not. When a vibration voltage signal is applied to the electrode 1, the corresponding capacitance signal is induced in each electrode 3 and the signal indicates the dielectric constant between the electrodes 3 and 1. The peak value of an output signal 14 of the amplifier 9 linearly changes corresponding to the dielectric constant between the electrodes 3 and 1, thus judging whether the tablet exists in the article 22 or not. |
