Patent ID: 7274193

Claim:
A potential sensor comprising: first and second detection electrodes opposed to a potential-measured object a potential of which is to be measured; and a movable shutter positioned between the detection electrodes and the potential-measured object with gaps thereto, wherein said movable shutter is configure to assume a first state and a second state, the first detection electrode being entirely exposed and the second detection electrode being entirely masked when the movable shutter assumes the first state, and the first detection electrode being entirely masked and the second detection electrode being entirely exposed when the movable shutter assumes the second state, and wherein said movable shutter is configured to be controlled by magnetic-field generation means, which generates a magnetic field substantially perpendicular to a movable direction of said movable shutter, and current application means, which supplies said movable shutter with a current substantially perpendicular to the movable direction of said movable shutter and to a direction of the magnetic field, thereby causing said movable shutter to assume said first state and said second state.