Grounding monitoring device
A grounding monitoring device is disclosed herein. In a described embodiment, the grounding monitoring device comprises a wrist strap comprising a first conductive portion for providing a first discharge path between a human arm and a ground; and a second conductive portion electrically isolated from the first conductive portion for providing a different second discharge path between the human arm and the ground. The grounding monitoring device further comprises a bipolar control voltage generator for applying a first voltage at a frequency f 0 to the first conductive portion and an opposite second voltage at the frequency f 0 to the second conductive portion; and an electrical circuit for: receiving a first total signal from the first conductive portion; receiving a second total signal from the second conductive portion; and forming an output signal based on a differential and common mode gains of the electrical circuit. The grounding monitoring device further comprises a comparator for comparing a portion of the output signal that corresponds to the frequency f 0 with a first threshold value; and comparing a portion of at least one of the first total signal and the second total signal that corresponds to the frequency f 0 with a second threshold value; wherein an alarm signal is activated depending on the comparisons made by the comparator.
1. A grounding monitoring device for use with a human part, the grounding monitoring device comprising:
a wrist strap comprising:
a first conductive portion for providing a first discharge path between the human part and a ground; and
a second conductive portion for providing a different second discharge path between the human part and the ground;
a signal source for applying a first voltage at a frequency to the first conductive portion and an opposite second voltage at the frequency to the second conductive portion;
an electrical circuit for:
receiving a first total signal from the first conductive portion;
receiving a second total signal from the second conductive portion;
forming an output signal based on a differential and common mode gains of the electrical circuit; and
a comparator for:
comparing a portion of the output signal that corresponds to the frequency with a first threshold value; and
comparing a portion of at least one of the first total signal and the second total signal that corresponds to the frequency with a second threshold value; wherein an alarm signal is activated if:
the portion of the output signal that corresponds to the frequency is greater than the first threshold value, and
the portion of at least one of the first total signal and the second total signal that corresponds to the frequency is less than the second threshold value.
2. The grounding monitoring device of claim 1 , wherein the electrical circuit comprises at least two operational amplifiers.
3. The grounding monitoring device of claim 1 , wherein the comparator comprises:
a first comparator for comparing the portion of the output signal that corresponds to the frequency with the first threshold value; and
a different second comparator for comparing the portion of at least one of the first total signal and the second total signal that corresponds to the frequency with the second threshold value.
4. The grounding monitoring device of claim 1 , wherein the alarm signal is activated if:
the portion of each one of the first total signal and the second total signal that corresponds to the frequency is less than the second threshold value.
5. The grounding monitoring device of claim 1 , wherein the alarm signal is not activated if:
the portion of at least one of the first total signal and the second total signal that corresponds to the frequency is greater than the second threshold value.
6. A grounding monitoring device for use with a human part, the grounding monitoring device comprising:
a wrist strap comprising:
a first conductive portion for providing a first discharge path between the human part and a ground; and
a second conductive portion for providing a different second discharge path between the human part and the ground;
a signal source for applying a first voltage at a frequency to the first conductive portion and an opposite second voltage at the frequency to the second conductive portion;
an electrical circuit for:
receiving a first total signal from the first conductive portion;
receiving a second total signal from the second conductive portion;
forming an output signal based on a differential and common mode gains of the electrical circuit; and
a comparator for:
comparing a portion of the output signal that corresponds to the frequency with a first threshold value; and
comparing a portion of at least one of the first total signal and the second total signal that corresponds to the frequency with a second threshold value,
wherein an alarm signal is activated depending on the comparisons made by the comparator, and
wherein the comparator comprises a filter for extracting:
the portion of the output signal that corresponds to the frequency; and
the portion of at least one of the first total signal and the second total signal that corresponds to the frequency.
7. The grounding monitoring device of claim 6 , wherein the filter comprises:
a first filter for extracting the portion of the output signal that corresponds to the frequency; and
a different second filter for extracting the portion of at least one of the first total signal and the second total signal that corresponds to the frequency.
8. A grounding monitoring device for use with a human part, the grounding monitoring device comprising:
a wrist strap comprising:
a first conductive portion for providing a first discharge path between the human part and a ground; and
a second conductive portion for providing a different second discharge path between the human part and the ground;
a signal source for applying a first voltage at a frequency to the first conductive portion and an opposite second voltage at the frequency to the second conductive portion;
an electrical circuit for:
receiving a first total signal from the first conductive portion;
receiving a second total signal from the second conductive portion;
forming an output signal based on a differential and common mode gains of the electrical circuit,
wherein the electrical circuit comprises:
a first resistor having a first value connecting a first output terminal of the signal source to the first conductive portion and to a non-inverting input of a first operational amplifier;
a second resistor having a second value connecting the first output terminal of the signal source to the ground;
a third resistor having the first value connecting a second output terminal of the signal source to the second conductive portion and to a non-inverting input of a second operational amplifier; and
a fourth resistor having the second value connecting the second output terminal of the signal source to the ground, and
wherein the grounding monitoring device further comprises a comparator for:
comparing a portion of the output signal that corresponds to the frequency with a first threshold value; and
comparing a portion of at least one of the first total signal and the second total signal that corresponds to the frequency with a second threshold value, wherein an alarm signal is activated depending on the comparisons made by the comparator.
9. A grounding monitoring device adapted to be connected to a wrist strap, the wrist strap comprising a first conductive portion for providing a first discharge path between a human part and a ground; and a second conductive portion for providing a different second discharge path between the human part and the ground, the grounding monitoring device comprising:
a signal source for applying a first voltage at a frequency to the first conductive portion and an opposite second voltage at the frequency to the second conductive portion;
an electrical circuit for:
receiving a first total signal from the first conductive portion;
receiving a second total signal from the second conductive portion;
forming an output signal based on a differential and common mode gains of the electrical circuit;
a comparator for:
comparing a portion of the output signal that corresponds to the first frequency with a first threshold value; and
comparing a portion of at least one of the first total signal and the second total signal that corresponds to the first frequency with a second threshold value; and wherein an alarm signal is activated if:
the portion of the output signal that corresponds to the frequency is greater than the first threshold value; and
the portion of at least one of the first total signal and the second total signal that corresponds to the frequency is less than the second threshold value.
10. The grounding monitoring device of claim 9 , wherein the electrical circuit comprises at least two operational amplifiers.
11. The grounding monitoring device of claim 9 , wherein the comparator comprises:
a first comparator for comparing the portion of the output signal that corresponds to the frequency with the first threshold value; and
a different second comparator for comparing the portion of at least one of the first total signal and the second total signal that corresponds to the frequency with the second threshold value.
12. The grounding monitoring device of claim 9 , wherein the comparator comprises a filter for extracting:
the portion of the output signal that corresponds to the frequency; and
the portion of at least one of the first total signal and the second total signal that corresponds to the frequency.
13. The grounding monitoring device of claim 12 , wherein the filter comprises:
a first filter for extracting the portion of the output signal that corresponds to the frequency; and
a different second filter for extracting the portion of at least one of the first total signal and the second total signal that corresponds to the frequency.
14. The grounding monitoring device of claim 9 , wherein the alarm signal is activated if:
the portion of each one of the first total signal and the second total signal that corresponds to the frequency is less than the second threshold value.
15. The grounding monitoring device of claim 9 , wherein the alarm signal is not activated if:
the portion of at least one of the first total signal and the second total signal that corresponds to the frequency is greater than the second threshold value.
16. The grounding monitoring device of claim 9 , wherein the electrical circuit comprises:
a first resistor having a first value connecting a first output terminal of the signal source to the first conductive portion and to a non-inverting input of a first operational amplifier;
a second resistor having a second value connecting the first output terminal of the signal source to the ground;
a third resistor having the first value connecting a second output terminal of the signal source to the second conductive portion and to a non-inverting input of a second operational amplifier; and
a fourth resistor having the second value connecting the second output terminal of the signal source to the ground.