Safety apparatus for hot-chassis electronic instruments

Claim 2

A safety indicator for use with electrical apparatus of the type employing an electrically conductive chassis which is to be desirably connected to a point of reference potential at a predetermined terminal of A.C. power lines via a plug having one terminal thereof connected to said chassis, said A.C. power lines serving to energize said apparatus when said plug is coacting therewith, comprising: a. a conductive member mounted on said electrical apparatus and electrically isolated from said chassis; b. an amplifier having an input terminal and an output terminal; c. means including a gas tube coupled between said member and said input terminal, said gas tube being conductive to provide an active indication in response to said member being returned to said reference potential point when said plug is connected to said power lines so that said chassis is not connected to said reference potential terminal of said A.C. power lines, and being nonconductive when said plug is connected to said power lines so that said chassis is at said reference potential point; and switching means coupled to said output terminal for automatically reversing the connections of said plug and said electrical apparatus to connect said chassis at said reference potential terminal of said A.C. power lines when said gas tube is conductive.

Claim 3

In an electrical apparatus of the type adapted to be plugged into and energized from A.C. power lines having at least two terminals, said apparatus including an electrically conductive chassis which is desirably connected to a point of reference potential at a predetermined terminal of said power lines, in combination therewith: safety apparatus for indicating when said electrical apparatus is properly plugged into said A.C. lines by determining when said chassis of said electrical apparatus is properly connected to said reference potential terminal of said A.C. power line, comprising: a. a conductive element mounted on said electrical apparatus and electrically isolated from said chassis; b. an amplifier having an input terminal and an output terminal; c. means coupled between said conductive element and said chassis, said means including a breakdown device having a breakdown potential rating less than the magnitude of potential on said A.C. lines connected in a circuit path between said conductive element and said input terminal of said amplifier, to develop a control signal at said input terminal of said amplifier when a circuit path is provided between said conductive element and said reference potential terminal, said control signal being determinative of said chassis being improperly plugged into said A.C. power lines; and d. switching means for connection of said A.C. lines to said electrical apparatus, said switching apparatus reversing its said connection in response to amplified control signals provided at said output terminal of said amplifier in response to said control signal.

Claim 4

In an electrical apparatus of the type adapted to be plugged into and energized from A.C. power lines having at least two terminals, said apparatus including an electrically conductive chassis which is desirably connected to a point of reference potential at a predetermined terminal of said power lines, in combination therewith: safety apparatus for indicating when said electrical apparatus is properly plugged into said A.C. lines by determining when said chassis of said electrical apparatus is properly connected to said reference potential terminal of said A.C. power line, comprising: a. a conductive element mounted on said electrical apparatus and electrically isolated from said chassis; b. an amplifier having an input terminal and an output terminal; c. means coupled between said conductive element and said chassis, said means including a breakdown device having a breakdown potential rating less than the magnitude of potential on said A.C. lines connected in a circuit path between said conductive element and said input terminal of said amplifier, to develop a control signal at said input terminal of said amplifier when a circuit path is provided between said conductive element and said reference potential terminal, said control signal being determinative of said chassis being improperly plugged into said A.C. power lines; and d. switching means for connection of said A.C. lines to said electrical apparatus, said switching apparatus reversing its said connection in response to amplified control signals provided at said output terminal of said amplifier in response to said control signal.

Claim 5

Safety apparatus for use with electrical apparatus of the type employing an electrically conductive chassis, said chassis utilized as a ground return for said apparatus and which is to be desirably connected to a point of reference potential available at one of two terminals associated with A.C. power lines, said A.C. power lines serving to energize said apparatus via a plug associated with said electrical apparatus for coacting with said A.C. power lines, said plug having one terminal connected to said chassis and another terminal connected to said electrical apparatus whereby said plug may undesirably coact with said A.C. power lines to cause said chassis to be connected with the terminal of said power lines not at refeRence potential, thus presenting a shock hazard to a consumer, said safety apparatus comprising: a. a conductive element mounted on said electrical apparatus and electrically isolated from said chassis; b. an amplifier having an input terminal, an output terminal, and a reference terminal connected to said chassis; c. first means coupled between said chassis and said conductive element, said means including a gas tube connected in a circuit path between said conductive element and said input terminal of said amplifier, said gas tube being rendered conductive when said element is returned to reference potential with said plug coacting with said A.C. power lines and with said chassis not at reference potential, and d. a loudspeaker arranged to be energized from said output terminal of said amplifier, whereby when a consumer or other operator touches said element his body impedance provides said reference potential return for said element, thereby causing said gas tube to glow and said loudspeaker to be energized.

Claim 6

Safety apparatus for use with electrical apparatus of the type employing an electrically conductive chassis, said chassis utilized as a ground return for said apparatus and which is to be desirably connected to a point of reference potential available at one of two terminals associated with A.C. power lines, said A.C. power lines serving to energize said apparatus via a plug associated with said electrical apparatus for coacting with said A.C. power lines, said plug having one terminal connected to said chassis and another terminal connected to said electrical apparatus whereby said plug may undesirably coact with said A.C. power lines to cause said chassis to be connected with the terminal of said power lines not at refeRence potential, thus presenting a shock hazard to a consumer, said safety apparatus comprising: a. a conductive element mounted on said electrical apparatus and electrically isolated from said chassis; b. an amplifier having an input terminal, an output terminal, and a reference terminal connected to said chassis; c. first means coupled between said chassis and said conductive element, said means including a gas tube connected in a circuit path between said conductive element and said input terminal of said amplifier, said gas tube being rendered conductive when said element is returned to reference potential with said plug coacting with said A.C. power lines and with said chassis not at reference potential, and d. a loudspeaker arranged to be energized from said output terminal of said amplifier, whereby when a consumer or other operator touches said element his body impedance provides said reference potential return for said element, thereby causing said gas tube to glow and said loudspeaker to be energized.