| 摘要 |
PURPOSE:To accurately measure the potential at an object to be measured in an electrostatic copying machine or the like in a non-contact manner, by employing a grid cutting off an incident electric flux and an electrode directly connected with an FET. CONSTITUTION:An electrode 17 placed on the stepped portion of an insulator 14 is connected to the gate of an FET16 housed in a tubular cap 11 having an electric flux incident opening 13. A detecting element 21 of such an arrangement is used to measure the potential at an object 18 to be measured to which a voltage is applied from a DC power source 19. In other words, a base 20 equipped with the detecting element 21 is provided with a grid 22 between the object 18 and the detecting element 21, and an FF circuit 23 is connected between the grid 22 and the ground. The grid 22 is periodically grounded by the FF circuit 23. Consequently, the electric line of force generated from the object 18 and reaching the electrode 17 in the detecting element 21 is interrupted by the grid 22, so that a voltage is induced between the drain and the source of the FET16. Measuring the voltage permits the surface potential of the object 18 to be measured in a non-contact manner. |
