Ground tether continuity monitor

• US 4,558,309 A
• Filed: 06/27/1983
• Issued: 12/10/1985
• Est. Priority Date: 06/27/1983
• Status: Expired due to Fees

• Current Assignee: Simco, Inc.
• Original Assignee: Simco Co., Inc.
• Inventors: Antonevich, John N.
• Primary Examiner(s): Rowland, James L.
• Assistant Examiner(s): MULLEN, THOMAS J
• Application Number:
  US06/507,977
• Time in Patent Office: 897 Days
• Field of Search: 340/649, 340/652, 340/506, 340/507, 340/510, 340/573, 340/658, 340/568, 340/565, 340/660, 361/42, 324/51 (US only), 128/734, 331/64, 331/65, 174/5 R, 174/5 SB, 174/5 SG, 174/6
• US Class Current: 340/649
• CPC Class Codes: A61B 5/276 Protection against electrode failure
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: G01R 31/54 Testing for continuity

Abstract

A monitor for sensing any break in electrical continuity between a body and earth when the body is coupled to earth by way of a grounding tether used to prevent build-up of static charges on such body. The monitor includes an oscillator circuit for generating A.C. output voltages which are adapted to actuate an alarm. Body capacitance and resistance are coupled by way of the tether across an impedance network either in the tuned circuit determining oscillator frequency or in the output load thereof whereby the resistance or inductance of the impedance network provides the path to ground for the body through its tether. With body capacitance and resistance components of the total impedance, variable elements in the impedance network are adjusted to diminish the circuit output voltage below the threshold voltage required to actuate the alarm when continuity exists while developing an output voltage level sufficient to actuate the alarm when a break in continuity occurs.

Claims

1. In combination with an electrically conductive tether for grounding a substantially non-conductive body to prevent build-up of static charges thereon, a monitor for detecting any break in electrical continuity between the body and ground, comprising:

frequency generator means for developing an A.C. output,

alarm means coupled to the output of said frequency generator means,

means associated with said frequency generator means and constituting an impedance network defining a frequency determining circuit therefor, said impedance network including a branch adapted to provide a continuous conductive path between said non-conductive body and ground when the tether is connected to the monitor, and

means to couple the distal end of the body-attached tether to ground through said impedance network, said impedance network being so constructed and arranged that the A.C. output of said frequency generator means when continuity exists between the body and ground is insufficient to actuate said alarm means by virtue of body capacitance present at the proximal end of the tether and, when any break in continuity between the body and ground occurs, absence of body capacitance will so change the characteristics of the A.C. output that the alarm means will be actuated.

2. The monitor of claim 1 wherein said impedance network includes feedback means for said frequency generator means.

3. The monitor of claim 2 wherein said frequency generator means comprises an oscillator circuit.

4. The monitor of claim 3 wherein coupling the tether to the impedance network detunes said oscillator circuit when continuity exists between the body and ground.

5. The monitor of claim 1 including means to adjust the impedance network of said frequency determining circuit.

6. The monitor of claim 1 wherein said frequency determining means comprises a Wien bridge.

7. The monitor of claim 6 wherein one arm of the Wien bridge includes a variable resistor.

8. The monitor of claim 1 wherein said impedance network is part of the load of said frequency generator means.

9. The monitor of claim 8 wherein coupling the tether to the impedance network acts to squelch the load when continuity exists.

10. The monitor of claim 8 including relay means coupled to the A.C. output for actuating said alarm means.

11. A monitor for sensing any break in electrical path between a substantially non-conductive body and ground by way of a conductive tether, comprising:

alarm means for alerting personnel of an open circuit between the body and ground,

frequency generator means adapted to develop an A.C. output sufficient to actuate said alarm means,

circuit means constituting a frequency determining network for said frequency generator means, said circuit means including a branch adapted to provide a continuous conductive path between said non-conductive body and ground when the tether is connected to the monitor, and

means for coupling the distal end of the bodyattached tether to ground through said frequency determining network so that body capacitance is introduced into said frequency determining network when continuity exists to effect oscillation of said frequency generator means at a level insufficient to actuate said alarm means, and when a break in continuity occurs between the body and ground, the absence of body capacitance will produce a change in the characteristics of the A.C. output above the level which will actuate said alarm means.

12. The monitor of claim 11 wherein the frequency determining network comprises an impedance.

13. The monitor of claim 12 wherein said impedance is adjustable.

14. The monitor of claim 12 wherein said frequency determining network comprises a Wien bridge.

15. The monitor of claim 14 wherein one arm of the Wien bridge includes an adjustable resistor.

16. A monitor for sensing any break in electrical path between a substantially non-conductive body and ground by way of a conductive tether, comprising:

an alarm for alerting personnel of an open circuit between the non-conductive body and ground,

an oscillator having an A.C. output coupled to said alarm,

an impedance network defining a frequency determining circuit for said oscillator and including a branch adapted to provide a continuous conductive path between said nonconductive body and ground when the body-attached tether is connected to the monitor,

said oscillator being so constructed and arranged in relation to said frequency determining circuit as to generate an oscillatory output insufficient to actuate said alarm when continuity exists between the body and ground through said impedance network, and, when any break in continuity occurs between the body and ground, the absence of body capacitance will produce a change in such oscillatory output as will cause actuation of said alarm.

17. The monitor of claim 16 wherein said impedance network includes a variable inductance.

18. The monitor of claim 16 wherein said impedance network includes adjustable components.

19. The monitor of claim 16 wherein said oscillator is of a Wien bridge configuration.

20. The monitor of claim 19 wherein one arm of the Wien bridge includes a variable resistor.