Patent ID: 7525222

Claim:
A sensor assembly for use at a protected area of a machine, the sensor assembly comprising: a power source producing a time-varying electric waveform; an electrically conductive emitter plate disposed adjacent to the protected area, electrically connected to the power source, and operating to generate a time-varying electric field within the protected area in response to application of the time-varying electric waveform from the power source to the emitter plate; plural electrically conductive sensor plates disposed adjacent to the protected area for receiving the time-varying electric field and producing respective electrical signals that vary in response to changes in the electric field; plural meters, each electrically connected to a respective one of the sensor plates, to measure a respective displacement current of the electrical signal produced at the respective sensor plate; and a signal analyzer electrically connected to the plural meters to monitor the respective displacement currents measured by the plural meters to find an average displacement current, sensing a disturbance in one of the displacement currents, and comparing the sensed displacement current disturbance to the average displacement current to determine whether the sensed displacement current disturbance is indicative of human tissue within the protected area.