Personnel grounding system tester

Claim 1

Apparatus for testing a personnel grounding system of the type used to prevent the buildup of electrostatic charges on the body and clothing of a worker engaged in the handling of charge-sensitive electronic devices, said personnel grounding system including first connector means electrically coupled to the body of said worker and means for coupling said first connector means through a safety resistance to a grounding connector means, said grounding connector means being adapted to connected to a grounding terminal which is coupled to earth ground, said apparatus determining whether the resistance of said personnel grounding system, measured from said first connector means through the body of said worker to said grounding connector means, is between two preselected values and providing an indicating signal when the resistance of said personnel grounding system is between said two preselected values, said apparatus comprising: (a) a voltage source having a first polarity and a second polarity; (b) a test connector for receiving said grounding connector means, said first polarity of said voltage source being connected to said test connector; (c) a first resistance, said first resistance being coupled to the second polarity of said voltage source; (d) a conductive pad disposed so that it may be touched by said worker while being electrically coupled to said first connector means; (e) a second resistance coupled between said first resistance and said conductive pad, said second resistance being less than the first resistance; (f) first voltage sensing means coupled between said first and second resistances for providing a high output when a voltage at its input is above a selected voltage and low output when a voltage at its input is below said selected voltage; (g) second voltage sensing means coupled between said second resistance and said conductive pad for providing a high output when a voltage at its input is above a selected voltage and a low output when a voltage at its input is below a selected voltage; (h) means for providing an indicating signal when said first voltage sensing means provides a high output signal and said second voltage sensing means provides a low output signal; and (i) the values of said first and second resistances being selected to provide a voltage at the input of said first voltage sensing means which is above said selected voltage and a voltage at the input of said second voltage sensing means which is below said selected voltage when the value of a resistance measured between said test connector and said conductive pad is between said two preselected values.