Continuous monitoring electrostatic discharge system

• US 5,422,630 A
• Filed: 09/06/1994
• Issued: 06/06/1995
• Est. Priority Date: 09/27/1991
• Status: Expired due to Fees

• Current Assignee: George D. Deneault
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Quinn, James A., Dempsey, John R., Deneault, George D., Bridge, Carl H.
• Primary Examiner(s): Hofsass, Jeffery A.
• Application Number:
  US08/302,072
• Time in Patent Office: 273 Days
• Field of Search: 340/649, 340/652, 340/660, 340/661, 340/662, 340/573, 361/212, 361/220, 361/42, 324/509, 324/705, 324/713, 324/538
• US Class Current: 340/661
• 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: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: G01R 31/54 Testing for continuity

Abstract

A monitoring system is shown to include a connector, having an input path and a current return path, for connecting a two section wrist strap to said connector, said two section wrist strap, when affixed to an operator'"'"'s wrist, would complete an electrical path between the input path and the current return path of the connector across the wrist skin surface. The monitoring system further includes a current source for providing an electrical current to the input path and a comparator for comparing a voltage at the input path to a high limit value and a low limit value and for providing an alarm signal whenever the voltage at the input path is not between the high limit value and the low limit value. With such an arrangement, an operator is ensured that a proper connection between the operator and ground is maintained thus significantly reducing the possibility of an electrostatic discharge harming an electronic component handled by the operator.

Claims

1. A monitoring system comprising:

(a) means, having an input path and a current return path, for connecting a device to said connecting means;

(b) means for providing a nonintermittent, constant and nonvarying magnitude, electrical current to the input path; and

(c) means for continuously comparing a voltage at the input path to a high limit value and a low limit value and for providing an alarm signal whenever the voltage at the input path is not between the high limit value and the low limit value indicating an electrostatic discharge.

2. The monitoring system as recited in claim 1 wherein the device is a two section wrist strap having a current return path and a resistor disposed in the current return path.

3. The monitoring system as recited in claim 1 wherein the continuously comparing means comprises:

(a) voltage source having a voltage with the high limit value;

(b) a voltage source having a voltage with the low limit value; and

(c) a pair of operational amplifiers, each one of the operational amplifiers having a first and a second input and an output, the first input of a first one of the pair of operational amplifiers connected to the input path of the connecting means and the second input of a second one of the pair of operational amplifiers connected to the input path of the connecting means, the second input of the first one of the pair of operational amplifiers connected to the voltage source having the high limit value and the first input of the second one of the pair of operational amplifiers connected to the voltage source having the low limit value.

4. The monitoring system as recited in claim 1 further comprising:

(a) second means, having an input path and a current return path, for connecting a second two section wrist strap to said second connecting means;

(b) second means for providing a nonintermittent, constant and nonvarying magnitude, electrical current to the input path of the second connecting means and for connecting a resistor disposed in the current return path of the second connecting means; and

(c) second means for comparing a voltage at the input path of the second connecting means to the high limit value and the low limit value and for providing an alarm signal whenever the voltage at the input path of the second connecting means is not between the high limit value and the low limit value.

5. The monitoring system as recited in claim 4 further comprising:

(a) third means, having an input path for connecting a work surface to said third connecting means;

(b) third means for providing a nonintermittent, constant and nonvarying magnitude, electrical current to the input path of the third connecting means; and

(c) third means for comparing a voltage at the input path of the third connecting means to the high limit value and the low limit value and for providing an alarm signal whenever the voltage at the input path of the third connecting means is not between the high limit value and the low limit value.

6. The monitoring system as recited in claim 5 further comprising:

(a) fourth means, having an input path for connecting a floor mat to said fourth connecting means;

(b) fourth means for providing a nonintermittent, constant and nonvarying magnitude, electrical current to the input path of the fourth connecting means; and

(c) fourth means for comparing a voltage at the input path of the fourth means to the high limit value and the low limit value and for providing an alarm signal whenever the voltage at the input path of the fourth connecting means is not between the high limit value and the low limit value.

7. The monitoring system as recited in claim 6 further comprising:

(a) fifth means, having an input path for connecting a solder pot to said fifth connecting means;

(b) fifth means for providing a nonintermittent, constant and nonvarying magnitude, electrical current to the input path of the fifth connecting means; and

(c) fifth means for comparing a voltage at the input path of the fifth connecting means to a second high limit value and for providing an alarm signal whenever the voltage at the input path of the fifth connecting means is greater than the second high limit value.

8. The monitoring system as recited in claim 7 further comprising:

(a) sixth means, having an input path for connecting a solder iron to said sixth connecting means;

(b) sixth means for providing a nonintermittent, constant and nonvarying magnitude, electrical current to the input path of the sixth connecting means; and

(c) sixth means for comparing a voltage at the input path of the sixth connecting means to the second high limit value and for providing an alarm signal whenever the voltage at the input path of the sixth connecting means is greater than the second high limit value.

9. A monitoring system comprising:

(a) a current source having an output terminal and a ground terminal, the ground terminal of the current source connected to an electrical ground, the current source adapted to provide a nonintermittent, predetermined constant and nonvarying magnitude of current;

(b) a resistor having a first terminal and a second terminal, the second terminal of the resistor connected to the electrical ground;

(c) a connector disposed between the output terminal of the current source and the first terminal of the resistor; and

(d) a comparator having an input connected to the output terminal of the current source to provide an alarm signal when a voltage at the output terminal of the current source varies beyond a predetermined limit indicating on electrostatic discharge.

10. The monitoring system as recited in claim 9 further comprising a two-section wrist strap having a signal input terminal and a signal output terminal and connected to the connector with the signal input terminal coupled to the output terminal of the current source and the signal output terminal connected to the first terminal of the resistor.

11. The monitoring system as recited in claim 9 further comprising:

(a) a second current source having an output terminal and a ground terminal, the ground terminal of the second current source connected to an electrical ground, the second current source adapted to provide a predetermined nonintermittent, constant and nonvarying magnitude of current;

(b) a second resistor having a first terminal and a second terminal, the second terminal of the second resistor connected to the electrical ground;

(c) a second connector disposed between the output terminal of the second current source and the first terminal of the second resistor; and

(d) a second comparator having an input connected to the output terminal of the second current source to provide an alarm signal when a voltage at the output terminal of the second current source varies beyond a predetermined limit.

12. The monitoring system as recited in claim 11 further comprising:

(a) a third current source having an output terminal and a ground terminal, the ground terminal of the third current source connected to an electrical ground, the third current source adapted to provide a nonintermittent, predetermined constant and nonvarying magnitude of current;

(b) a third connector disposed between the output terminal of the third current source and the ground terminal, the third connector adapted to connect to a work surface; and

(c) a third comparator having an input connected to the output terminal of the third current source to provide an alarm signal when a voltage at the output terminal of the third current source varies beyond a predetermined limit.

13. The monitoring system as recited in claim 12 further comprising:

(a) a fourth current source having an output terminal and a ground terminal, the ground terminal of the fourth current source connected to an electrical ground, the fourth current source adapted to provide a nonintermittent, predetermined constant and nonvarying magnitude of current;

(b) a fourth connector disposed between the output terminal of the fourth current source and the ground terminal, the fourth connector adapted to connect to a floor mat; and

(c) a fourth comparator having an input connected to the output terminal of the fourth current source to provide an alarm signal when a voltage at the output terminal of the fourth current source varies beyond a predetermined limit.

14. The monitoring system as recited in claim 13 further comprising:

(a) a fifth current source having an output terminal and a ground terminal, the ground terminal of the fifth current source connected to an electrical ground, the fifth current source adapted to provide a nonintermittent, predetermined constant and nonvarying magnitude of current;

(b) a fifth connector disposed between the output terminal of the fifth current source and the ground terminal, the fifth connector adapted to connect to a solder pot; and

(c) a fifth comparator having an input connected to the output terminal of the fifth current source to provide an alarm signal when a voltage at the output terminal of the fifth current source varies above a predetermined limit.

15. The monitoring system as recited in claim 14 further comprising:

(a) a sixth current source having an output terminal and a ground terminal, the ground terminal of the sixth current source connected to an electrical ground, the sixth current source adapted to provide a nonintermittent, predetermined constant and nonvarying magnitude of current;

(b) a sixth connector disposed between the output terminal of the sixth current source and the ground terminal, the sixth connector adapted to connect to a solder iron test probe; and

(c) a sixth comparator having an input connected to the output terminal of the sixth current source to provide an alarm signal when a voltage at the output terminal of the sixth current source varies above a predetermined limit.

16. A method of protecting circuit elements from electrostatic discharges from an operator comprising the steps of:

(a) coupling a two section wrist strap having an input path and an output path to an operator such that the operator completes a signal path between the input path and the output path of the two section strap;

(b) providing a predetermined nonintermittent, constant and nonvarying magnitude, electrical current to the input path of the two section strap and connecting a bleeding resistor between the output path of the two section strap and an electrical current return path;

(c) comparing continuously a voltage at the input path of the two section strap to a high limit value and a low limit value; and

(d) providing an alarm signal whenever the voltage at the input path of the two section strap is not between the high limit value and the low limit value.

17. The method as recited in claim 16 further comprising the steps of:

(a) coupling a device to a ground terminal;

(b) providing at an input path to the device a predetermined nonintermittent, constant and nonvarying magnitude, electrical current;

(c) comparing continuously a voltage at the input path of the device to the high limit value and the low limit value; and

(d) providing an alarm signal whenever the voltage at the input path of the device is not between the high limit value and the low limit value.

18. The method as recited in claim 17 further comprising the steps of:

(a) coupling a floor mat to a ground terminal;

(b) providing at an input path to the floor mat a predetermined nonintermittent, constant and nonvarying magnitude, electrical current;

(c) comparing continuously a voltage at the input path of the floor mat to the high limit value and the low limit value; and

(d) providing an alarm signal whenever the voltage at the input path of the floor mat is not between the high limit value and the low limit value.

19. The method as recited in claim 18 further comprising the steps of:

(a) coupling a solder pot to a ground terminal;

(b) providing at an input path to the solder pot a predetermined nonintermittent, constant and nonvarying magnitude, electrical current;

(c) comparing continuously a voltage at the input path of the solder pot to a second different high limit value; and

(d) providing an alarm signal whenever the voltage at the input path of the solder pot is above the second different high limit value.

20. A method as recited in claim 19 further comprising the steps of:

(a) coupling a solder iron to a solder iron test probe;

(b) providing at an input path to the solder iron test probe a predetermined nonintermittent, constant and nonvarying magnitude, electrical current;

(c) comparing continuously a voltage at the input path of the solder iron test probe to the second different high limit value; and

(d) providing an alarm signal whenever the voltage at the input path of the solder iron test probe is above the second different high limit value.