SYSTEM FOR MONITORING CHASSIS POTENTIAL AND GROUND CONTINUITY

• US 3,697,808 A
• Filed: 11/23/1970
• Issued: 10/10/1972
• Est. Priority Date: 11/23/1970
• Status: Expired due to Term

• Current Assignee: Joo Chan Lee
• Original Assignee: Joo Chan Lee
• Inventors: Lee, Joo Chan
• Primary Examiner(s): Sliney, D. X.
• Application Number:
  US05/091,617
• Time in Patent Office: 687 Days
• Field of Search: 317/9A,10,18R,18A,18B,18C,18D
• US Class Current: 361/46
• CPC Class Codes: A61B 5/276 Protection against electrode failure
• CPC Class Codes: A61B 5/29 for permanent or long-term implantation
• CPC Class Codes: H02H 11/001 in case of incorrect or interrupted earth connection disconnection by breaking of earth connection H02H5/105
• CPC Class Codes: H02H 3/162 for ac systems

Abstract

A monitoring system controls the application of power from a grounded power source to an electrical load in a chassis connected to the source by the line, neutral and ground leads of a power cable. Control is exerted by monitoring the level of leakage power current flowing in the ground lead of the cable and disconnecting the power source from the line lead of the cable when the level is such that a 5 millivolt drop would occur across the ground lead. This maintains the chassis at a potential of no more than 5 millivolts with respect to ground. An RF signal injected into the neutral lead of the cable causes RF current to flow in the ground lead by reason of the capacitive coupling between the load and the chassis when continuity exists between the chassis and the source ground. The RF current is monitored in order to disconnect the power source when such current drops below a predetermined level indicating that an inadequate or insufficient connection exists between the chassis and ground, situations that interfere with properly monitoring the level of leakage power current through the ground lead.

Claims

1. A monitoring system for controlling the application of power from a grounded power source to a chassis-mounted load by way of a cable that includes a plurality of leads, comprising:

a. power switch means associated with said leads for applying power from said source to said load when said power switch means is enabled and to disconnect said source when said power switch means is disabled;

b. a two-state control means for enabling said power switch means when said control means has a first state and disabling said power switch means when said control means has a second state;

c. means to inject an RF signal into one of said leads for producing an RF signal in a second of said leads;

d. supervision means associated with said second lead for switching said control means to said second state when the RF signal in said second lead decreases below a predetermined level; and

e. means responsive to the flow of power current from said source for causing said control means to switch to said second state when said power current exceeds a predetermined value.

2. A monitoring system according to claim 1 wherein said second lead is attached to said chassis, including ground current sensing means associated with said second lead for switching said control means to said second state when the potential of said chassis relative to ground exceeds a predetermined value.

3. A monitoring system according to claim 1 wherein:

a. an RF signal generator is coupled by a transformer into said one lead and an RF signal appears in said second lead by reason of the coupling between said leads and between said load and said chassis; and

b. said supervision means includes a current transformer coupled to said second lead, a rectifier for rectifying the output of said current transformer, a biasable active device for operating said control means when the bias on said device exceeds a predetermined level, and bias means responsive to the output of said rectifier for providing bias to said active device.

4. A monitoring system according to claim 3 wherein said bias means is adjustable for establishing the level of the output of said rectifier at which said active device will operate said control means whereby the cable length can be compensated for.

5. A monitoring system according to claim 3 including means functionally relating the coupling of said transformer to the level of power current drawn from said source whereby the flow of more than a preselected level of power current reduces the RF signal in said ground lead below said predetermined level.

6. Monitor means for use with a chassis containing an electrical load connected to a grounded power source by way of at least one line lead, a neutral lead, and a ground lead attached to said chassis, comprising:

a. operable control means;

b. an RF signal generator associated with said leads whereby said load is adapted to couple an RF signal into said ground lead; and

c. supervision means responsive to the level of the RF signal in said ground lead for operating said control means when said level decreases below a predetermined level.

7. Monitor means according to claim 6 including ground current sensing means associated with said ground lead for operating said control means when leakage power current in said ground lead exceeds a predetermined level.

8. Monitor means according to claim 6 including power switch means connected to said leads and responsive to the operation of said control means for disconnecting said power source from said load.

9. Monitor means according to claim 6 wherein:

a. the output of said RF signal generator is coupled by means of a transformer into said neutral lead;

b. said supervision means includes a current transformer coupled to said ground lead, a rectifier for rectifying the output of said current transformer, a biasable active device for operating said control means when the bias on said device exceeds a predetermined level, and bias means responsive to the output of said rectifier for providing bias to said active device.

10. Monitor means according to claim 9 where the transformer by which the RF signal is coupled into said neutral lead saturates when the flow of power current from said source exceeds a predetermined value whereby the bias on said device decreases below said predetermined level.

11. Monitor means according to claim 10 including power switch means connected to said leads and responsive to the operation of said control means for disconnecting said power source from said load.

12. Monitor means according to claim 9 wherein said current transformer saturates when the flow of power current in said ground lead exceeds a predetermined value whereby the bias on said device decreases below said predetermined level.

13. A monitor module for use with a grounded power source having a line bus, a neutral bus, and a ground bus comprising:

a. a receptacle having a line contact, a neutral contact and a ground contact corresponding to the buses, and adapted to receive the plug of a pOwer cable by which an electrical load can be connected to said source;

b. RF signal generator means between one of said buses and its corresponding contact for injecting supervisory current into said cable;

c. supervision means between a second bus and its corresponding contact for detecting the level of supervisory current flowing through the last mentioned contact; and

d. control means operable by said supervision means when the flow of said supervisory current through the contact corresponding to said second bus decreases below a predetermined level.

14. A monitor module according to claim 13 including power switch means between the line bus and its corresponding contact of said receptacle, said power switch being responsive to said control means for connecting the line contact to the line bus only while the supervisory current flowing through the contact corresponding to said second bus exceeds said predetermined level.

15. A monitor module according to claim 13 including means responsive to the flow of power current through the contact corresponding to said second bus for operating said control means when the level of the last mentioned flow exceeds a predetermined level.

16. A monitor module according to claim 13 wherein said RF generator means is constructed and arranged so that the amount of supervisory current injected into said cable is functionally related to the level of power current flowing through the contact corresponding to said one bus.

17. A monitor module according to claim 13 wherein said supervision means is constructed and arranged so that the level of supervisory current able to be detected thereby is functionally related to the level of leakage power current flowing through the contact corresponding to said second bus.

18. A monitor module according to claim 13 including a power switch responsive to the operation of said control means for disconnecting power from said source to said line when the supervisory current flowing through the contact corresponding to said second bus is less than a predetermined value.

19. A method for monitoring the continuity of a connection between a chassis and a system ground through a ground lead in a cable providing power to an electrical load in the chassis by means of a line lead and a neutral lead, comprising:

a. injecting an RF signal into a first lead other than said ground lead; and

b. detecting the presence of an RF signal in the ground lead.

20. The method of claim 19 including the step of providing a passive component between said first lead and said chassis.

21. Monitor means associated with the application of power to an electrical load from a source comprising a line bus, a neutral bus, and a ground bus, comprising:

a. interconnection means adapted to connect said load to the buses for energizing said load;

b. said interconnection means including a lead adapted to be connected to one bus, and an RF signal generator adapted to be connected between another bus and said load for causing RF current to flow in said lead;

c. two-state control means; and

d. means responsive to the level of RF current in said lead for determining, at least in part, the state of said control means when said RF current decreases below a predetermined level.

22. Monitor means for use with a chassis containing an electrical load connected to a grounded power source by way of a line lead, a neutral lead, and a ground lead attached to said chassis, comprising:

a. a two-state control means having a first state only when the connection between the chassis and the power source ground is continuous and the potential difference is less than a predetermined value, and having a second state either when said connection is discontinuous or when said potential difference is more than a predetermined value;

b. ground current sensing means responsive to the potential difference between the chassis and the power source ground for determining, at least In part, the state of said control means; and

c. ground continuity supervision means responsive to the continuity of the connection between the chassis and the power source ground for determining, at least in part, the state of said control means.

23. Monitor means for use with a chassis containing an electrical load connected to a grounded power source by way of a line lead, a neutral lead, and a ground lead attached to said chassis, comprising:

A. a two-state control means; and

B. ground current sensing means responsive to the potential difference between the chassis and the power source ground for determining, at least in part, the state of said control means, and including;

a. a current transformer coupled to said ground lead;

b. a rectifier for rectifying the output of said current transformer;

c. a biasable active device for causing said control means to occupy its first state only when the bias on said device has a predetermined level; and

d. bias means responsive to the output of said rectifier for providing bias to said device.