Image Number 4 for United States Patent #8446277.
Various proximity detection zones for work sites that require personnel to be in close proximity to various hazardous elements, such as machines, mobile equipment, remotely controlled machines, and operated vehicles can be shaped to fit specific equipment or work area configurations and may include one or more silent zones within the proximity warning zone in which an alarm is not sounded. The zones are determined by overlapping magnetic fields that expand and collapse at a selected operating frequency. Devices sense and measure the strength of the magnetic fields in which they are located and use the information to determine if they are in a silent or warning zone. Thus, it is possible to produce silent zones having desired shapes.