Patent ID: 7119554
Filing Date: 2006-10-10
Classification: G01D,G01R,G01V

Abstract:
1. An electrical capacitance proximity sensor for detecting a nearby object, comprising: a sensor section which includes a first electrode used as a detecting electrode, a second electrode used as other than said detecting electrode, and a guard electrode provided between said first and second electrodes, said guard electrode being insulated from said first and second electrodes; a detecting circuit section which detects said nearby object by monitoring a variation in an electrostatic capacitance generated by said first electrode to output a detecting signal; a connecting cable which includes first and second wires to couple said sensor section to said detecting circuit section, wherein: said first electrode and said guard electrode are coupled to one end of said first and second wires, respectively; said detecting circuit section receives a first oscillation signal according to said electrostatic capacitance generated by said first electrode from the other end of said first wire and supplies a second oscillation signal having the same phase and the same voltage as said first oscillation signal to the other end of said second wire, said detecting circuit section taking a normal operation mode for detecting said nearby object and taking a self-diagnostic mode for making a diagnostic of a correct connection between said sensor section and said detecting circuit section, and wherein said detecting circuit section further includes: a switching controller which supplies said second oscillation signal to said other end of said second wire in said normal operation mode and stops supplying said second oscillation signal to said other end of said second wire in said self-diagnostic mode; and a control circuit which detects an incorrect connection between said sensor section and said detecting circuit section in said self-diagnostic mode based on changes in said detecting signal by comparing said detecting signal in said normal operation mode with said detecting signal in said self-diagnostic mode.