Ground isolation monitoring apparatus having a protective circuit
AssigneeTektronix, Inc.
InventorsStanley H. Tate, Donald K. Roberts, Carl E. Hollingsworth, William R. Nute
Life of this patent
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Abstract
A ground isolation monitoring apparatus having a protective circuit is provided for use between an AC power source and a utilization device, such as an electronic instrument. The protective circuit permits operation of the utilization device with earth ground disconnected, automatically reconnecting earth ground if a hazardous voltage or current appears on device chassis or exposed metal parts. The protective circuit also monitors neutral-to-earth ground continuity and shuts off AC power to the utilization device if the ground path opens or if the impedance thereof increases. Various other features may be provided to ensure safe operation of the device.
Claims16
An apparatus for monitoring an earth ground path between an AC power source and an electronic device, comprising:
- means for isolating a portion of said earth ground path from earth ground;
- detection means coupled to said isolated portion of said earth ground path for detecting a hazardous electrical condition thereon, said detection means comprising a full-wave rectifier and a pulse-generating circuit for developing a pulse when the voltage or current on said isolated portion of said earth ground path exceeds a predetermined value;
- and
- control circuit means comprising electronic switch means responsive to said pulse from said detection means for reconnecting earth ground to said isolated portion of said earth ground path.
An apparatus in accordance with claim 5 wherein said control circuit means further comprises an electronic switch connected between earth ground and said isolated portion of said earth ground path.
An apparatus for monitoring an earth ground path between an AC power source and an electronic device, comprising:
- means for isolating a portion of said earth ground path from earth ground;
- detection means coupled to said isolated portion of said earth ground path for detecting a hazardous electrical condition thereon;
- control circuit means responsive to said detection means for reconnecting earth ground to said isolated portion of said earth ground path;
- and
- a ground continuity monitoring circuit connected between a neutral conductor of said AC power source and earth ground for detecting a voltage therebetween and producing an output if said voltage exceeds a predetermined value, said control circuit means further being responsive to the output of said ground continuity monitoring circuit for connecting said device to earth ground and at the same time disconnecting said device from said AC power source.
A monitoring apparatus for use between an AC power source and a utilization device, comprising:
- interconnection means comprising a line conductor, a neutral conductor, and an earth ground conductor for electrically connecting and disconnecting said device to and from said AC power source;
- means for electrically isolating a portion of said earth ground conductor thereby to isolate said device from earth ground;
- ground-continuity circuit means comprising a voltage-sensing resistor, a peak detector, and an electronic switch for detecting a voltage between said neutral conductor and said earth ground conductor and activating said switch when said voltage exceeds a predetermined level;
- control circuit means coupled to said interconnection means and being responsive to the activation of said switch for disconnecting said device from said AC power source;
- and
- further detection means coupled to the isolated portion of said earth ground conductor for detecting a hazardous electrical condition thereon, said control means being responsive to said further detection means for reconnecting said device to earth ground.
Dependencies are inferred from the claim text.