Wrist strap integrity check circuitry

• US 6,035,260 A
• Filed: 04/23/1997
• Issued: 03/07/2000
• Est. Priority Date: 04/23/1997
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Guthrie, Warren E., Pohribnij, Walter Jerry
• Primary Examiner(s): Kemper, Melanie A.
• Application Number:
  US08/842,069
• Time in Patent Office: 1,049 Days
• Field of Search: 702/58, 702/116, 324/500, 324/509, 324/510, 340/573, 340/649, 340/650, 361/212, 361/220
• US Class Current: 702/58
• CPC Class Codes: A61N 1/14 Leading-off electric charges, e.g. by earthing carrying-off electrostatic charges, in general H05F3/00

Abstract

Improved electronic circuitry incorporated into a tag attached to a user worn wrist strap of a static electrical discharge dissipation system. The electronic circuitry monitors the electrical connection of the wrist strap from the user to ground, and comprises a discharge resistor and a discharge resistor check circuit for monitoring the accuracy of the discharge resistor. The electronic circuitry further comprises a skin resistance check circuit for monitoring the electrical connection of the wrist strap to the user, and a ground fault detect circuit for monitoring the electrical connection of the wrist strap to ground.

Claims

1. In a static electrical discharge dissipation system having a dissipation device which is worn by a user and a conductive line for electrically connecting the dissipation device to ground, the improvement comprising a tag which electrically communicates with the dissipation device and includes electronic circuitry for monitoring the electrical connection of the dissipation device from the user to ground, the electronic circuitry of the tag comprising:

a discharge resistor;

a microprocessor having a sensor circuit which is in electrical communication with the discharge resistor and includes;

a discharge resistor check circuit for monitoring the accuracy of the discharge resistor, the discharge resistor check circuit being configured to generate a discharge resistor signal;

a skin resistance check circuit for monitoring the electrical connection of the dissipation device to the user, the skin resistance check circuit being configured to generate a skin resistance signal; and

a ground fault detect circuit for monitoring the electrical connection of the dissipation device to ground, the ground fault detect circuit being configured to generate a ground fault signal;

the microprocessor being configured to multiplex the sensor circuit to facilitate the generation of the discharge resistor, skin resistance, and ground fault signals;

a transmission circuit which is in electrical communication with the sensor circuit for transmitting the discharge resistor, skin resistance, and ground fault signals to an interrogator unit.

2. The electronic circuitry of claim 1 wherein said discharge resistor check circuit is configured to perform a high limit check of the discharge resistor and a low limit check of the discharge resistor.

3. The electronic circuitry of claim 1 wherein the dissipation device comprises a static wrist strap having the tag attached thereto.

4. The electronic circuitry of claim 1 wherein the tag into which the electronic circuitry is incorporated comprises a transmit only tag.

5. The electronic circuitry of claim 1 wherein the transmission circuit is configured to transmit the discharge resistor, skin resistance, and ground fault signals via a direct sequence spread spectrum having a data rate of approximately 33.33 kbps.

6. The electronic circuitry of claim 5 wherein the discharge resistor, skin resistance, and ground fault signals are transmitted by the transmission circuit via a carrier frequency of approximately 2414 Mhz +/- 1 Mhz.

7. The electronic circuitry of claim 1 wherein the transmission circuit is configured to transmit the discharge resistor, skin resistance, and ground fault signals to the interrogator unit at selected transmission cycles.

8. The electronic circuitry of claim 7 wherein each of the transmission cycles comprises approximately five repetitions of the signals, with each repetition being separated by a random interval of approximately three seconds.

9. The electronic circuitry of claim 7 wherein the transmission circuit is configured such that the transmission cycles occur at random intervals of approximately five minutes.

10. The electronic circuitry of claim 1 wherein the transmission circuit is configured to transmit the ground fault signal to the interrogator unit immediately upon the occurrence of an interrupt within the electrical connection of the tag to ground.

11. The electronic circuitry of claim 1 wherein:

the discharge resistor check circuit is configured to periodically monitor the accuracy of the discharge resistor;

the skin resistance check circuit is configured to periodically monitor the electrical connection of the dissipation device to the user; and

the ground fault detect circuit is configured to continuously monitor the electrical connection of the dissipation device to ground.

12. The electronic circuitry of claim 1 further comprising an alarm circuit for generating an audible alarm in response to certain conditions sensed by the electronic circuitry.

13. The electronic circuitry of claim 12 wherein said alarm circuit is configured to generate an audible alarm is when the accuracy of the discharge resistor as monitored by the discharge resistor check circuit is outside the range of approximately 1 Megohm +/- 30%.

14. The electronic circuitry of claim 12 wherein said alarm circuit is configured to generate an audible alarm when at least one reading of the user'"'"'s skin resistance as monitored by the skin resistance check circuit is above 10 Megohms.

15. The electronic circuitry of claim 12 wherein said alarm circuit is configured to generate an audible alarm when a ground fault condition is monitored by the ground fault detect circuit.

16. In a static electrical discharge dissipation system having a dissipation device which is worn by a user and a conductive line for electrically connecting the dissipation device to ground, a method for monitoring the electrical connection of the dissipation device from the user to ground comprising the steps of:

(a) providing a tag which electrically communicates with the dissipation device and includes electronic circuitry having a discharge resistor and a microprocessor including a sensor circuit which is in electrical communication with the discharge resistor;

(b) multiplexing the sensor circuit of the microprocessor to;

monitor the accuracy of the discharge resistor and generate a discharge resistor signal corresponding thereto via a discharge resistor check circuit of the sensor circuit;

monitor the electrical connection of the dissipation device to the user and generate a skin resistance signal corresponding thereto via a skin resistance check circuit of the sensor circuit; and

monitor the electrical connection of the dissipation device to ground and generate a ground fault signal corresponding thereto via a ground fault detect circuit of the sensor circuit;

(c) transmitting the discharge resistor, skin resistance, and ground fault signals to an interrogator unit via a transmission circuit of the electronic circuitry.

17. The method of claim 16 wherein step (b) comprises performing a high limit check of the discharge resistor and a low limit check of the discharge resistor.

18. The method of claim 16 wherein step (c) comprises transmitting the discharge resistor, skin resistance, and ground fault signals to the interrogator unit via a carrier frequency of approximately 2414 Mhz +/- 1 Mhz.

19. The method of claim 16 wherein step (c) comprises transmitting the discharge resistor, skin resistance, and ground fault signals to the interrogator unit at selected transmission cycles.

20. The method of claim 19 wherein step (c) comprises transmitting the signals at transmission cycles which each comprise approximately five repetitions of the signals, with each repetition being separated by a random interval of approximately three seconds.

21. The method of claim 19 wherein step (c) comprises transmitting the signals at transmission cycles which occur at random intervals of approximately five minutes.

22. The method of claim 16 further comprising the step of:

(d) generating an audible alarm in response to certain conditions of the electronic circuitry via an alarm circuit of the electronic circuitry.

23. The method of claim 22 wherein step (d) comprises generating an audible alarm when the accuracy of the discharge resistor as monitored by the alarm circuit is outside of the range of 1 Megohms +/- 30%.

24. The method of claim 22 wherein step (d) comprises generating an audible alarm when at least one reading of the user'"'"'s skin resistance as monitored by the skin resistance check circuit is above 10 Megohms.

25. The method of claim 22 wherein step (d) comprises generating an audible alarm when a ground fault is monitored by the ground fault detect circuit.

26. The method of claim 16 wherein step (c) comprises transmitting the ground fault signal to the interrogator unit immediately upon the occurrence of an interrupt within the electrical connection of the dissipation device to ground.

27. The method of claim 16 wherein step (b) comprises:

periodically monitoring the accuracy of the discharge resistor via the discharge resistor check circuit;

periodically monitoring the electrical connection of the dissipation device to the user via the skin resistance check circuit; and

continuously monitoring the electrical connection of the dissipation device to ground via the ground fault detect circuit.

28. In a static electrical discharge dissipation system having a dissipation device which is worn by a user and a conductive line for electrically connecting the dissipation device to ground, the improvement comprising a tag which electrically communicates with the dissipation device and includes a electronic circuitry for monitoring the electrical connection of the dissipation device from the user to ground, the electronic circuitry of the tag comprising:

a discharge resistor;

a microprocessor having a sensor circuit which is in electrical communication with the discharge resistor and includes;

a discharge resistor check circuit which is operative to monitor the accuracy of the discharge resistor and generate a discharge resistor signal corresponding thereto;

a skin resistance check circuit which is operative to monitor the electrical connection of the dissipation device to the user and generate a skin resistance signal corresponding thereto; and

a ground fault detect circuit which is operative to monitor the electrical connection of the dissipation device to ground and generate a around fault signal corresponding thereto;

the microprocessor being configured to multiplex the sensor circuit to facilitate the generation of the discharge resistor, skin resistance, and ground fault signals.

29. In a static electrical discharge dissipation system having a dissipation device which is worn by a user and a conductive line for electrically connecting the dissipation device to ground, the improvement comprising a tag which electrically communicates with the dissipation device and includes electronic circuitry for monitoring the electrical connection of the dissipation device from the user to ground, the electronic circuitry of the tag comprising:

a discharge resistor; and

a microprocessor having a sensor circuit which is in electrical communication with the discharge resistor;

the microprocessor being configured to multiplex the sensor circuit in a manner facilitating the generation of a discharge resistor signal corresponding to a monitored status of the accuracy of the discharge resistor, a skin resistance signal corresponding to a monitored status of the electrical connection of the dissipation device to the user, and a ground fault signal corresponding to a monitored status of the electrical connection of the dissipation device to ground.