Corona detection apparatus

Claim 1

Apparatus for assuring the availability of electrosta-tic charge controlling corona for controlling the electrostatic charge level on charge-retaining material, comprising: first and second electrically conductive reference surfaces; a first corona source for producing a first stream of electric charges between said first corona source and said first reference sur-face; a second corona source for producing a second stream of charges between said second corona source and said second refer-ence surface; an electrical conductor in the path of said first stream of electric charges produced by said first corona source wherein an electric current is produced in said conductor as a result of a portion of the said first stream of electric charges impinging on said electrical conductor; and means responsive to the said conductor current in said electrical conductor for energizing said second corona source when the magnitude of the current in said conductor is equal to or less than a predeter-mined magnitude as a result of loss of corona from said first corona source whereby the uninterrupted availability of corona produced electric charges for controlling the electrostatic charge level on charge-retaining material is thereby assured for material that is initially passed between said first corona source and said first reference surface, and subsequently between said second corona source and said second reference surface.