CIRCUIT FOR SENSING THE ABSENCE OF A SAFETY GROUND IN AN ELECTRICALLY OPERATED TRANSPORT VEHICLE SYSTEM

• US 3,825,915 A
• Filed: 09/20/1972
• Issued: 07/23/1974
• Est. Priority Date: 09/20/1972
• Status: Expired due to Term

• Current Assignee: Ronald C. Dow
• Original Assignee: Ronald C. Dow
• Inventors: Dow, Ronald C.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/290,449
• Time in Patent Office: 671 Days
• Field of Search: 324/51,52,54 317/18A,18B 340/256 246/1R,1C,169R
• US Class Current: 340/649
• CPC Class Codes: G01R 31/50 Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections testing of sparking plugs H01T13/58
• CPC Class Codes: H02H 11/001 in case of incorrect or interrupted earth connection disconnection by breaking of earth connection H02H5/105

Abstract

The embodiment of the invention disclosed herein is directed to a circuit for sensing the absence of a safety ground from electrically operated machines or vehicles. The circuit includes a magnetic frame having first and second magnetic circuit paths extending about the frame with a common circuit portion thereof from which excitation energy is induced into the magnetic frame. A single turn closed loop winding is positioned about one portion of the magnetic frame and a load winding is positioned about another portion of the magnetic frame. During normal conditions, when the closed loop winding is maintained, this indicating good connection for the safety ground, the magnetic flux path is primarily directed about the magnetic frame to maintain maximum excitation of the load winding. This load winding is then connected to a transistor circuit which operates an indicating device of any suitable kind. Upon disconnection of the safety ground, the closed loop winding becomes open circuited and the impedance of the magnetic field in the magnetic frame changes abruptly to cause a substantial reduction in the magnetic circuitry associated with the load winding. This then causes automatic energization of the indicator for indicating that safety ground has been lost.

Claims

1. In an electrically operated transport vehicle system, the combination comprising:

a ground conductor, sensing circuit means including an inductive reactance element for providing magnetic circuits, movable contact means providing spaced apart physical and electrical contact elements engageable with said ground conductor and adapted to be moved along said ground conductor, said movable contact means providing a safety ground connection of the transport vehicle with said ground conductor, means for operatively connecting said sensing circuit with said movable contact means to change the state of the magnetic circuits within said sensing circuit when a break in continuity is sensed between said ground conductor and said contact means, and indicator means responsive to said sensing circuit means to indicate that an ungrounded condition exists.

2. The electrically operated transport vehicle system according to claim 1 wherein said inductive reactance element includes a transformer having first, second and third magnetic circuit portions, said first magnetic circuit portion receiving an excitation voltage for producing magnetic circuits within said transformer, said second magnetic portion receiving a load winding responsive to the magnetic circuit associated therewith for producing an output voltage, and said third circuit portion receiving a short circuit loop which is connected to said contact means for providing a high magnetic impedance of said second magnetic portion when said short circuit loop is in a closed loop condition, and for providing a low magnetic impedance of said second magnetic portion when said short circuit loop is in an open circuit condition.

3. The electrically operated transport vehicle system according to claim 2 wherein said load winding is connected to a conductive switching element for operating the same during conditions when said closed loop path is maintained, said current conductive means operatively connected to said indicator means to maintain said indicator in an off condition when said short circuit loop is maintained closed and automatically to render said indicator means operative when said short circuit loop path is opened.

4. The electrically operated transport vehicle system according to claim 1 wherein said reactance means includes a magnetic frame providing two spaced apart magnetic circuits, each magnetic circuit having a common leg therebetween, An excitation winding positioned on said common leg for inducing magnetic flux paths through said two spaced apart magnetic circuits, a load winding connected to one of said two spaced apart magnetic circuits outwardly of said central portion for providing an output voltage sufficient to energize a transistor circuit when the impedance of the other of said two spaced apart magnetic circuits is maintained in a high state, and disconnection of said movable contact means with said ground conductor will cause a change in impedance of said magnetic circuit automatically to indicate the absence of a safety ground.