Capacitive Item Sensor for Supermarket Scanner
Original Publication Date: 1985-Jun-01
Included in the Prior Art Database: 2005-Feb-18
A capacitive item sensor for supermarket scanners is described which detects items without requiring the raised rails presently required to mount sensors. These rails interfere with large items. A capacitive item sensor has a flat bed 11, flush mounted and adequate and with well localized sensitivity. It uses a simple inductive ratio arm bridge to detect capacitive changes caused by grocery items. A pair of transformer windings 12 applies alternating voltages matched to a few parts per million in vector amplitude to two of three metal plates 13 making up two capacitors. These may be fabricated to sufficient accuracy using lithography, or simply from metal plates. The center plate 14 is coupled to an FET transimpedance amplifier 15.