Switch contact wetting with low peak instantaneous current draw

Patent metadata

Field	Value
Publication number	US-9837219-B2
Application number	US-201314141755-A
Country	US
Kind code	B2
Filing date	Dec 27, 2013
Priority date	Dec 27, 2013
Publication date	Dec 5, 2017
Grant date	Dec 5, 2017

Abstract

A contact wetting circuit 100 is disclosed for supplying wetting current to sense the state of dry contacts of a switch SW 1 setting for an electronic device 10 . The contact wetting circuit includes an RC circuit 110 having a resistor R 1 and a capacitor C 1 , and a controller 120 connected to a power supply 130 of the device. The controller supplies a first voltage to the RC circuit to produce a charging current having an average current and/or a peak current below the wetting current parameter of the dry contacts. The charging current is used to charge the capacitor C 1 during the first time period. The controller stops the supply of the first voltage to the RC circuit after sufficient charging to allow the charged capacitor C 1 to supply a second voltage, across the switch SW 1 , to produce a wetting current. Thereafter, the controller polls and senses the state of the switch SW 1 , and performs certain operations accordingly.

First claim

The invention claimed is:

1. A contact wetting circuit for supplying wetting current to dry contacts of a switch for an electronic device, comprising:
a controller connected to a power supply and to an RC circuit which is connected to the switch, the controller configured to:
supply a first voltage to the RC circuit to produce a charging current having an average current below or a peak current below a wetting current parameter of the dry contacts of the switch, the wetting current parameter defining a minimum current that is necessary for cleaning surface oxidation on the dry contacts of the switch to be conductive, the power supply providing to the controller the average current below or peak current below the wetting current parameter of the dry contacts of the switch, the charging current charging a capacitor of the RC circuit during a first time period; and
stop the supply of the first voltage to the RC circuit after sufficient capacitor charging to allow a wetting current for the dry contacts of the switch to be transmitted from the capacitor to the switch, the wetting current produced from a second voltage supplied from the charged capacitor of the RC circuit during a second time period.

2. The circuit of claim 1 , further comprising the RC circuit including a resistor and the capacitor, wherein the capacitor is connected in parallel to the switch and the resistor is connected to the controller.

3. The circuit of claim 1 , wherein the controller is further configured to sense a state of the switch after the second time period.

4. The circuit of claim 3 , wherein the controller includes a general input output pin (GPIO) through which to supply the first voltage during the first time period and to sense the state of the switch during a third time period after the second time period.

5. The circuit of claim 3 , wherein the controller is further configured to output a third voltage comprising a low logic level after a third time period.

6. The circuit of claim 1 , wherein the first voltage corresponds to a high logic level of the controller.

7. The circuit of claim 1 , wherein an amount of the charging current is controlled according to the first voltage supplied from the controller and a resistance of a resistor of the RC circuit.

8. The circuit of claim 1 , wherein the power supply is from the electronic device, which is a low powered or self-powered electronic device.

9. The circuit of claim 1 , wherein the second voltage supplied from the capacitor has a voltage corresponding to a high logic level of the controller.

10. The circuit of claim 1 , wherein the second time period has a maximum duration that is insufficient for the capacitor to discharge through current leakage, to below the second voltage.

11. A contact wetting method of supplying wetting current to dry contacts of switch for an electronic device via an RC circuit and a controller connected to a power supply, comprising:
supplying a first voltage from the controller to the RC circuit to produce a charging current during a first time period, the charging current having an average current below or a peak current below a wetting current parameter of the dry contacts of the switch, the wetting current parameter defining a minimum current that is necessary for cleaning surface oxidation on the dry contacts of the switch to be conductive, the power supply providing to the controller the average current below or peak current below the wetting current parameter of the dry contacts of the switch, the charging current further charging a capacitor of the RC circuit during the first time period; and
stopping the supply of the first voltage to the RC circuit after sufficient capacitor charging to allow a wetting current to be transmitted from the capacitor to the switch, the wetting current produced for the dry contacts of the switch from a second voltage supplied from the charged capacitor of the RC circuit during a second time period.

12. The method of claim 11 , further comprising sensing through the controller a state of the switch during a third time period after the second time period.

13. The method of claim 12 , wherein sensing and supplying are performed by the controller via a general input output pin (GPIO) of the controller.

14. The method of claim 12 , further comprising outputting, via the controller, a third voltage comprising a low logic level after a third time period.

15. The method of claim 11 , wherein the first voltage corresponds to a high logic level of the controller.

16. The method of claim 11 , wherein the charging current is based on the first voltage supplied from the controller and a resistance of a resistor of the RC circuit.

17. The method of claim 11 , wherein the power supply is from the electronic device, which is a low powered or self-powered electronic device.

18. The method of claim 11 , wherein the second voltage supplied from the capacitor has a voltage corresponding to a high logic level of the controller.

19. The method of claim 11 , wherein the second time period has a maximum duration that is insufficient for the capacitor to discharge through current leakage, to below the second voltage.

20. A contact wetting method of supplying wetting current to sense the state of a pair of dry contacts of a switch for an electronic device, comprising:
producing a charging current to charge a capacitor over a time period using power drawn from a power supply for self-power of the electronic device, the charging current having an average current below or a peak current below a wetting current parameter of the dry contacts, the wetting current parameter defining a minimum current that is necessary for cleaning surface oxidation on the dry contacts of the switch to be conductive, the power supply providing the average current below or peak current below the wetting current parameter of the dry contacts of the switch;
stopping the production of the charging current;
producing a wetting current for wetting the dry contacts using power supplied from the charged capacitor, the wetting current transmitted from the capacitor to the switch; and
sensing an ON or CLOSED state and an OFF or OPEN state of the switch during producing of the wetting current.

Assignees

• Schneider Electric Usa Inc

Inventors

• Jefferies Kevin

Classifications

• H01H9/167

  Circuits for remote indication · CPC title

• H01H1/605 Primary

  Cleaning of contact-making surfaces by relatively high voltage pulses · CPC title