| 摘要 |
Apparatus for monitoring the dielectric composition of articles, particularly articles such as blisterpacks and laminated boards. The apparatus comprises an amplifying circuit including a capacitor between the electrodes (1, 3) of which an article (22) is moved in use. The gain of the amplifying circuit varies with the capacitance of the capacitor so that the amplifying circuit provides an output signal, the peak value of the output signal varying with the dielectric constant of the article (22) between the capacitor electrodes (1, 3), Typically the amplifying circuit includes an operational amplifier (9) the non-inverting input (10) of which is connected to a ground potential(6) and the inverting input (8) is connected to one electrode (3) of the capacitor. A feedback loop (11) is applied between the output (14) of the operational amplifier (9) and the inverting input (8) of the operational amplifier to force the inverting input to the same potential as the non-inverting input. Typically an oscillating signal source (5) is connected to the other electrode (1) of the capacitor. |
