Magnetic field sensor with error calculation

• US 10,837,943 B2
• Filed: 05/26/2017
• Issued: 11/17/2020
• Est. Priority Date: 05/26/2017
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Romero, Hernan D.
• Primary Examiner(s): Patidar, Jay
• Assistant Examiner(s): Andrews, Brent J
• Application Number:
  US15/606,325
• Publication Number:
  US 20180340911A1
• Time in Patent Office: 1,271 Days
• CPC Class Codes: G01D 3/036 on measuring arrangements themselves
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01N 2223/052 reflection
• CPC Class Codes: G01N 27/9006 Details, e.g. in the structure or functioning of sensors
• CPC Class Codes: G01R 33/0283 in which a current or voltage is generated due to relative movement of conductor and magnetic field
• CPC Class Codes: G01R 33/06 using galvano-magnetic devices
• CPC Class Codes: G01R 33/09 Magnetoresistive devices
• CPC Class Codes: G01R 33/10 Plotting field distribution ; Measuring field distribution
• CPC Class Codes: G01V 3/107 using compensating coil or loop arrangements

Abstract

A magnetic field sensing system may include a first magnetic field sensing element; a second magnetic field sensing element; means for generating a first magnetic field having a first non-zero frequency; means for generating a second magnetic field having a second frequency; a conductive target positioned to generate a reflected magnetic field in response to the first magnetic field; means for producing a first signal representing the first magnetic field and the reflected magnetic field during a first alternating time period; means for producing a second signal representing the second magnetic field during a second alternating time period; means for calculating an error value as a function of the first and second signals, wherein the error value is based, at least in part, on the second signal during the first time period; and means for applying the error value to the first signal during the first alternating time period.

Claims

1. A system comprising:

at least one coil configured to;

generate a first magnetic field having a first frequency that induces a first reflected magnetic field in a conductive target during a first time period, wherein the first reflected magnetic field has a first magnetic field strength; and

generate a second magnetic field having a second frequency that induces a second reflected magnetic field in the conductive target during a second time period, wherein the second reflected magnetic field has a second magnetic field strength that is different than the first magnetic field strength;

at least one first magnetic field sensing element configured to detect the first magnetic field and the first reflected magnetic field during the first time period and to detect the second magnetic field and the second reflected magnetic field during the second time period;

at least one second magnetic field sensing element configured to detect the first magnetic field and the first reflected magnetic field during the first time period and to detect the second magnetic field and the second reflected magnetic field during the second time period; and

a processing circuit coupled to receive a respective output signal from the at least one first and at least one second magnetic field sensing elements and to calculate an error value of the system,

wherein the processing circuit to calculate the error value comprises;

summing the output signal from the at least one first magnetic field sensing elements and the output signal from the at least one second magnetic field sensing elements to form a summation signal; and

subtracting the output signal from the at least one second magnetic field sensing elements from the output signal from the at least one first magnetic field sensing elements to form a subtraction signal.

2. The system of claim 1 wherein the second frequency is substantially zero and the second reflected magnetic field strength is substantially zero.

3. The system of claim 1 wherein the first magnetic field comprises a first frequency that induces eddy currents in the conductive target that generate the first reflected magnetic field.

4. The system of claim 1 wherein the error value is based on measurements taken during the first time period and the processing circuit is configured to apply the error value to measurements taken during the second time period.

5. The system of claim 1 wherein the at least one first magnetic field sensing element is placed so that its axis of maximum sensitivity is aligned with the first magnetic field.

6. The system of claim 1 wherein the processing circuit to calculate the error value further comprises the processing circuit dividing the summation signal by the subtraction signal.

7. A system comprising:

at least one coil configured to;

generate a first magnetic field having a first non-zero frequency; and

generate a second magnetic field having a second frequency;

a conductive target positioned to generate a reflected magnetic field in response to the first magnetic field;

one or more magnetic field sensing elements configured to;

produce a first signal representing detection of the first magnetic field and the reflected magnetic field; and

produce a second signal representing detection of the second magnetic field; and

a processing circuit configured to;

receive the first and second signals; and

calculate an error value of the system as a function of the first and second signals,

sum the first signal and the second signal to form a summation signal; and

subtract the first signal from the second signal to form a subtraction signal.

8. The system of claim 7 wherein the calculated error value is independent of a position of the conductive target.

9. The system of claim 7 wherein first magnetic field has a frequency sufficiently high to induce an eddy current in the conductive target.

10. The system of claim 9 wherein the reflected magnetic field is produced by the eddy current.

11. The system of claim 7 wherein the second frequency is substantially low so that it does not induce a reflected field from the conductive target.

12. The system of claim 11 wherein the second frequency is substantially zero.

13. The system of claim 7 wherein the first magnetic field is generated during a first time period and the second magnetic field is generated during a second time period.

14. The system of claim 13 further comprising a processing circuit to calculate an error value based on measurements taken during the second time period and apply the error value to measurements taken during the first time period.

15. The system of claim 13 wherein the first and second time periods are non-overlapping time periods.

16. The system of claim 7 wherein the processing circuit configured to calculate the error value further comprises the processing circuit configured to divide the summation signal by the subtraction signal.

17. A method comprising:

generating a first magnetic field having a first, non-zero frequency;

generating a second magnetic field having a second frequency;

inducing, by the first magnetic field, a reflected magnetic field from a conductive target;

producing a first signal, by one or more magnetic field sensing elements, representing the first magnetic field and the reflected magnetic field;

producing a second signal, by the one or more magnetic field sensing elements, representing the second magnetic field; and

calculating an error value as a function of the first and second signals,

summing the first signal and the second signal to form a summation signal; and

subtracting the first signal from the second signal to form a subtraction signal.

18. The method of claim 17 wherein the calculated error value is independent of a position of the conductive target.

19. The method of claim 17 wherein first magnetic field has a frequency sufficiently high to induce an eddy current in the conductive target, wherein the reflected magnetic field is produced by the eddy current.

20. The method of claim 17 wherein the second frequency is substantially low so that the second magnetic field does not induce a reflected magnetic field from the conductive target.

21. The method of claim 20 wherein the second frequency is substantially zero.

22. The method of claim 17 wherein:

generating the first magnetic field comprises generating the first magnetic field during a first time period; and

generating the second magnetic field comprises generating the second magnetic field during a second time period.

23. The method of claim 22 wherein the first and second time periods are non-overlapping time periods.

24. The method of claim 22 further comprising:

generating the first signal during the first time period representing;

generating the second signal during the second time period;

calculating an error value based on the first signal measured during the first time period; and

applying the error value to the second signal during the second time period.

25. The method of claim 17, wherein calculating the error value further comprises dividing the summation signal by the subtraction signal.

26. A system comprising:

a first magnetic field sensing element;

a second magnetic field sensing element;

means for generating a first magnetic field having a first non-zero frequency;

means for generating a second magnetic field having a second frequency;

a conductive target positioned to generate a reflected magnetic field in response to the first magnetic field;

means for producing a first signal representing the first magnetic field and the reflected magnetic field during a first alternating time period;

means for producing a second signal representing the second magnetic field during a second alternating time period;

means for calculating an error value as a function of the first and second signals, wherein the error value is based, at least in part, on the second signal during the first time period; and

means for applying the error value to the first signal during the first alternating time period.