APPARATUS AND METHODS FOR PROXIMITY SENSING CIRCUITRY

• US 20090140727A1
• Filed: 11/29/2007
• Published: 06/04/2009
• Est. Priority Date: 11/29/2007
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Rollins, George E., Chen, Weihua, Sufariu, Diana A., Kulkarni, Prachi S.
• Granted Patent: US 9,599,448 B2
• Time in Patent Office: Days
• US Class Current: 324/207.160
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: G01B 7/14 for measuring distance or clearance between spaced objects or spaced apertures G01B7/30 takes precedence

Abstract

An inductive proximity sensor is disclosed. The proximity sensor includes a source circuit with an inductive element configured to deliver energy to a resonator when a source current is changed. In various embodiments, the source current is provided a step current source. In various embodiment, the source current is provided by constant current source coupled to the inductive element by a switch. Apparatus and methods for operating the inductive proximity sensor are disclosed.

Claims

1. An inductive sensing circuit comprising:

a source circuit for energizing an inductive proximity sensor, consisting essentially of;

a current source;

a switch coupled to the current source, and

an inductive source element coupled to the switch; and

a resonant circuit coupled to the inductive source element.

2. The circuit of claim 1, wherein the resonant circuit includes a bifurcated inductor.

3. The circuit of claim 2, wherein the bifurcated inductor includes two inductive elements coupled in parallel

4. The circuit of claim 1, wherein the inductive source element is configured to energize the resonant circuit when the switch is open.

5. The circuit of claim 1, wherein the switch is a semiconductor switch.

6. The circuit of claim 1, wherein the current source is a constant current source or a step current source.

7. A method of powering an inductive proximity sensor, comprising:

applying a source current to an inductive circuit until a first current in the inductive circuit obtains at least a steady state condition;

changing an amplitude of the source current at a first time;

monitoring a second current flowing from the inductive circuit to a resonant circuit having a bifurcated inductance, the second current less than or equal to the source current;

re-establishing the first current at a second time if an amplitude of the second current is less than a specified value, and

imposing a blanking time interval while re-establishing the first current.

8. The method of claim 7, further comprising sensing proximity while monitoring.

9. The method of claim 7, wherein changing includes discontinuing the source current using a switching device.

10. The method of claim 7, wherein an changing includes step adjusting the amplitude of the source current.

11. The method of claim 7, wherein applying the source current includes applying while the inductive circuit is connected to a resonant circuit.

12. A proximity detector, comprising:

a current loop including a current source and an inductive circuit;

a control for initiating a change in a current flowing in the inductive circuit, the control located in the current loop; and

an inductive proximity sensor coupled to the inductive circuit, the inductive proximity sensor including a resonator circuit, the resonant circuit having a bifurcated inductance, wherein the inductive proximity sensor is configured such that the current flowing in the inductive circuit and a voltage across the resonator circuit are initially unchanged upon activating the control.

13. The detector of claim 12, wherein the current flowing in the inductive circuit and the voltage across the resonant circuit are initially independent of a present state of the resonant circuit when the control is activated.

14. The detector of claim 12, wherein a timing module is configured to impose a gating time interval upon activating the control.

15. The detector of claim 12, further comprising a shunt resistance configured to quench oscillations in the resonant circuit.

16. The detector of claim 12, wherein the control includes a switching device.

17. The detector of claim 12, wherein the control includes a means for step adjusting the current source.

18. The detector of claim 12, wherein the current flowing in the inductive circuit is characterized by the voltage across the resonant circuit independent of a resonant state of the resonant circuit.

19. The detector of claim 12, wherein the inductive current loop is configured to reduce contribution of off-resonance frequency components to a resonant frequency of oscillation of the resonant circuit.

20. A process control system, comprising:

a source current circuit including a current source and an inductive circuit;

a control for initiating a change in a current flowing in the inductive circuit, the control located in the source current circuit;

an inductive proximity sensor coupled to the inductive circuit, the inductive proximity sensor including a resonator circuit, the resonant circuit having a bifurcated inductance, wherein the inductive proximity sensor is configured such that the current flowing in the inductive circuit and a voltage across the resonator circuit are initially unchanged upon activating the control; and

a processor coupled to at least one of the source circuit and the inductive proximity sensor, wherein the processor is configured to process signals associated with eddy currents generated in a metal.

21. The system of claim 20, wherein a rate of decay of the current flowing from the inductive circuit is based on the eddy currents.

22. The system of claim 20, wherein the control includes at least one of a switching element and a means for step adjusting an amplitude of the current source.

23. The system of claim 20, wherein the source current circuit is configured to reduce contribution of off-resonance frequency components to a resonant oscillation associated with the resonant circuit.

24. The system of claim 20, wherein the current flowing in the inductive circuit is characterized by the voltage across the resonant circuit independent of a resonant state of the resonant circuit.

25. The system of claim 20, wherein the current flowing in the inductive circuit and the voltage across the resonant circuit are initially independent of a present state of the resonant circuit when the control is activated.