GROUND SAFE SYSTEM

• US 3,783,340 A
• Filed: 09/07/1972
• Issued: 01/01/1974
• Est. Priority Date: 09/07/1972
• Status: Expired due to Term

• Current Assignee: Richard S. Becker
• Original Assignee: Richard S. Becker
• Inventors: Becker, Richard S.
• Primary Examiner(s): Trammell, James D.
• Application Number:
  US05/286,864
• Time in Patent Office: 481 Days
• Field of Search: 340/256 324/51 317/18B,146,9D
• US Class Current: 361/50
• CPC Class Codes: G01R 27/18 Measuring resistance to earth , i.e. line to ground
• CPC Class Codes: H02H 11/001 in case of incorrect or interrupted earth connection disconnection by breaking of earth connection H02H5/105

Abstract

The chassis of the equipment which is to be monitored is connected in series with a closed switch, the secondary winding of a first transformer, and the primary winding of a second transformer to a ground terminal such as is commonly found in a grounded wall outlet. The primary winding of the first transformer is supplied with a high frequency signal from an oscillator. The secondary winding of the second transformer is connected to a transistorized alarm circuit. As long as the equipment is properly grounded, the high frequency signal will flow through the series circuit and keep the alarm inoperative. If the ground line of the hospital equipment is broken or increases greatly in its resistance, the high frequency signal will be interrupted and this will activate the alarm circuit. The system includes a redundant ground connection to the chassis of the equipment.

Claims

1. A system for monitoring the ground lead connection of an electrically conducting piece of equipment to a ground terminal comprising a first transformer having a primary winding and at least one secondary winding, an oscillator connected to the primary winding of the first transformer for generating an alternating electrical signal in the primary and secondary windings of the first transformer at a predetermined, relatively high frequency, a second transformer having primary and secondary windings, means for providing an additional connection between the electrically conducting piece of equipment and the ground terminal in parallel with the ground lead connection, the additional ground connection means including means for directly connecting the secondary winding of the first transformer, the primary winding of the second transformer, the electrically conducting piece of equipment and the ground connection in a series circuit, and means connected to the secondary winding of the second transformer and responsive to the high frequency signal for providing an indication when the high frequency signal circulating in the series circuit falls below a predetermined magnitude.

2. A system for monitoring the conductivity of a grounding connection from an electrically conductive chassis of a piece of medical equipment to a ground terminal, the electrically conductive equipment being of the type which is connected by leads to a power source, the monitoring system comprising a first transformer having a primary winding and at least a secondary winding, means connected to the primary winding of the first transformer for generating an alternating electrical signal having a high frequency in the range between 10 KHz and 100 KHz, a second transformer having a primary winding and a secondary winding, means separate from the power leads for providing an additional connection between the equipment chassis and the ground terMinal, the additional ground terminal connection means including means for connecting the secondary winding of the first transformer and the primary winding of the second transformer in series between the ground terminal and the chassis of the equipment to be monitored, detector means connected to the secondary winding of the second transformer and responsive to the high frequency signal appearing at the secondary winding of the second transformer for providing an indication of the decrease in the conductivity of the grounding connection upon the decrease by a predetermined amount in the intensity of the high frequency signal.

3. A monitoring system as recited in claim 2 wherein the means for connecting the secondary winding of the first transformer and the primary winding of the second transformer in series with the equipment to be monitored includes means for selectively increasing the resistance in the series circuit in order to provide a test of the monitoring system.

4. A system for separately and simultaneously monitoring the conductivity of the grounding connections of a plurality of electrically conductive pieces of medical equipment to a ground terminal, the equipment being of the type which is connected by leads to a power source, the system comprising a first transformer having a primary winding and a plurality of secondary windings, means for generating an alternating electrical signal having a high frequency in the range of 10 KHz to 100 KHz in the primary winding of the first transformer, a plurality of detector circuits responsive to the high frequency signals appearing at the secondary windings of the first transformer, each detector circuit including a transformer having a primary and a secondary winding, means separate from the power leads for providing separate additional connections between the chassis of the pieces of equipment and the ground terminal, the addition ground terminal connection means including means for separately connecting each of the primary windings of the detector transformers and a separate one of the secondary windings of the first transformer in series between the ground terminal and the chassis of a separate piece of electrical equipment to be monitored.

5. A monitoring system as recited in claim 4 wherein the means for generating an alternating signal causes an alternating signal having a voltage substantially equal to 5 millivolts to flow in the means for separately connecting the primary windings of the detector transformers.