Device and method for capacitive measurement by a floating bridge

• US 8,149,002 B2
• Filed: 11/22/2006
• Issued: 04/03/2012
• Est. Priority Date: 11/24/2005
• Status: Active Grant

• Current Assignee: Fogale Sensors
• Original Assignee: Nanotec Corporation
• Inventors: Ossart, Frédéric, Roziere, Didier
• Primary Examiner(s): He, Amy
• Application Number:
  US12/093,582
• Publication Number:
  US 20080231292A1
• Time in Patent Office: 1,959 Days
• Field of Search: 324/662, 324/663, 324/688
• US Class Current: 324/688
• CPC Class Codes: G01B 7/08 using capacitive means
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G01R 17/10 AC or DC measuring bridges
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2017/9615 using three electrodes per touch switch
• CPC Class Codes: H03K 2217/960755 Constructional details of capacitive touch and proximity switches

Abstract

A device for capacitive measurement by a floating bridge, including: a sensor module including at least one measuring electrode and at least one guard electrode arranged close to a target connected to a general earth, at least one integrated circuit for capacitive measurement, provided with a guard to which the guard electrode is connected, having an input connected to the measuring electrode, a guard connected to the reference earth of the integrated circuit, an excitation output connected to the general earth, a measurement output, and structure for supplying the integrated circuit for capacitive measurement in floating mode.

Claims

1. A device for capacitive measurement by a floating bridge, comprising:

a sensor module comprising at least one measuring electrode and at least one guard electrode arranged close to a target connected to a general earth,

a guard to which said guard electrode is connected,

at least one integrated circuit for capacitive measurement, and comprising (i) a measurement input and (ii) an excitation output for measuring capacitances between electrodes connected respectively to said measurement input and to an excitation signal generated on said excitation output, (iii) an earth terminal and (iv) a measurement output,

means for supplying said integrated circuit for capacitive measurement in floating mode, and

wherein said measurement input is connected to said measuring electrode, said guard is connected to the reference earth terminal of said integrated circuit, and said excitation output is connected to said general earth.

2. The device according to claim 1, wherein said means for floating supply are arranged to achieve an electrical isolation of the integrated circuit for capacitive measurement, with regard to the general earth.

3. The device according to claim 1, further comprising means for differential amplification for generating, from the output signal of the integrated circuit for capacitive measurement, an output signal referenced to the general earth.

4. The device according to claim 1, further comprising amplification means arranged between the excitation output of the integrated circuit for capacitive measurement and the general earth.

5. The device according to claim 4, further comprising means for supplying the amplification means at a voltage which can be higher than that of the integrated circuit for capacitive measurement.

6. The device according to claim 1, further comprising a second guard electrode surrounding the first guard electrode), wherein said second guard electrode is connected to the general earth.

7. The device according to claim 1, in which the sensor module comprises a first and a second measuring electrodes, substantially parallel, and between which is situated is a target electrode connected to the general earth, wherein said first and second measuring electrodes, are connected respectively to a first and a second inputs of the integrated circuit for capacitive measurement, and are surrounded respectively by first and second guard electrodes.

8. The device according to claim 7, wherein said first and second guard electrodes are connected to each other and to the guard by means of a common guard connection.

9. The device according to claim 7, wherein said first and second guard electrodes are connected to the guard via a first and a second guard connections, respectively.

10. The device according to claim 1, further including a plurality of measuring electrodes surrounded by a guard electrode connected to the guard.

11. The device according to claim 10, further including switching means connected at input to the plurality of measuring electrodes and at output to an input of the integrated circuit for capacitive measurement, situated at the inside of the guard and controlled by means for controlling and processing.

12. The device according to claim 11, further including optocoupling means arranged between the switching means and the means for control and processing.

13. The device according to claim 10, characterized further including a plurality of integrated circuits for capacitive measurement each connected at input to a measuring electrode and at output, each having their excitation output connected to the input of first switching means, of which the output is connected to the general earth, and their measurement output connected to the input of second switching means generating at output a multiplexed capacitive measurement signal, said first and second switching means being situated inside the guard and controlled by means for control and processing.

14. The device according to claim 1, wherein said integrated circuit for capacitive measurement comprises charge transfer capacitance/digital converter means.

15. The device according to claim 1, wherein said integrated circuit for capacitive measurement comprises a Delta Sigma capacitance-digital converter.

16. The device according to claim 1, wherein said integrated circuit for capacitive measurement is designed to generate digital output signals, characterized in that it also comprises optocoupling means for processing the output signals of the integrated circuit for capacitive measurement.

17. The device according to claim 1, wherein said integrated circuit for capacitive measurement is situated close to the electrodes of the sensor module.

18. The device according to claim 1, wherein said integrated circuit for capacitive measurement is remote from the electrodes by means of a coaxial or triaxial cable.

19. The device according to claim 1, wherein said integrated circuit for capacitive measurement comprises differential inputs and has a single guard.

20. The device according to claim 1, further including means for floating supply for supplying the components arranged inside the guard.

21. The device according to claim 20, wherein said supply means are chosen from the following means:

direct current/direct current (DC-DC) conversion means, alternating current/direct current (AC-DC) conversion means, at least one choke coil, at least one electrical cell, at least one battery or any other energy/DC converter.

22. The device according to claim 21, in which the supply means comprise DC-DC or AC-DC conversion means, wherein said DC-DC or AC-DC conversion means comprise a transformer comprising as primary circuit, a coil excited by an alternating signal referenced to a general earth and, as a secondary circuit, a receptor coil connected to rectifier means for generating one or a plurality of floating direct current voltages.

23. The device according to claim 22, wherein the transformer is of the “

planar”

type.

24. A miniaturized device for capacitive measurement according to claim 1, produced in the form of a printed circuit on which the measuring electrode is etched, said printed circuit receiving the integrated circuit for capacitive measurement, the floating supply means, and the means of connection of the integrated circuit with external equipments.

25. The device according to claim 1, implemented in an anti-collision system.

26. The device according to claim 1, implemented in a shape recognition system.

27. The device according to claim 1, implemented in a strain gauge, wherein it is fixed onto a reference support and has at least one measuring electrode targeting the surface of a part being subjected to a deformation to be measured.

28. The device according to claim 1, implemented in a dimensional metrology system.

29. The device according to claim 1, implemented in a biosensor system.

30. The device according to claim 1, implemented for a characterization of materials.

31. A method for capacitive measurement by floating bridge using a sensor module, comprising steps of:

arranging at least one measuring electrode and at least one guard electrode close to a target connected to a general earth,

connecting said guard electrode to a guard,

providing at least one integrated circuit for capacitive measurement, comprising (i) a measurement input and (ii) an excitation output for measuring capacitances between electrodes connected respectively to said measurement input and to an excitation signal generated on said excitation output, (iii) an earth terminal and (iv) a measurement output,

supplying said integrated circuit for capacitive measurement in floating mode,

connecting said measurement input to said measuring electrode,

connecting said guard to the reference earth terminal of said integrated circuit, and

connecting said excitation output to said general earth.

32. The method according to claim 31, further comprising a step of differential amplification of the output signal of the integrated circuit for capacitive measurement, for generating an output signal referenced to the general earth.

33. The method according to claim 31, further comprising a step of amplification of the excitation signal generated by the integrated circuit for capacitive measurement.

34. The method according to claim 31, used in a device provided with a plurality of measuring electrodes, further comprising for a step of connecting with a switch a measuring electrode from the plurality of measuring electrodes at the input of the integrated circuit for capacitive measurement.

35. The method according to claim 31, used in a device provided with a plurality of measuring electrodes connected at the input of a plurality of integrated circuits for capacitive measurement, further comprising steps of switching of the excitation outputs of the plurality of integrated circuits for capacitive measurement to the general earth and switching of the measurement outputs of the plurality of integrated circuits for capacitive measurement to a multiplexed output.