Method and apparatus for providing information from a speed and direction sensor

• US 6,815,944 B2
• Filed: 10/29/2002
• Issued: 11/09/2004
• Est. Priority Date: 01/31/2002
• Status: Expired due to Term

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Forrest, Glenn, Vig, Ravi, Towne, Jay M.
• Primary Examiner(s): Deb, Anjan K.
• Application Number:
  US10/282,528
• Publication Number:
  US 20030141862A1
• Time in Patent Office: 742 Days
• Field of Search: 324/207.2, 324/165, 324/179, 324/207.18, 324/207.12, 324/173, 324/117.H, 324/607, 324/207.25, 324/174, 341/15, 341/53, 341/179, 341/182
• US Class Current: 324/179
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01D 5/24457 Failure detection
• CPC Class Codes: G01P 3/488 delivered by variable reluctance detectors
• CPC Class Codes: H03K 5/082 with an adaptive threshold

Abstract

A method and apparatus for providing information from a speed and direction sensor is disclosed. The method and apparatus detect the presence of a ferromagnetic object as it moves past a sensor. The sensor determines speed and direction information regarding the ferromagnetic object, and further provides information relating to the environment surrounding the sensor or object, such as the status of an air gap between the sensor and the moving object, and the temperature of the environment in which the sensor or object is disposed.

Claims

1. A magnetic article proximity detector for detecting a magnetic article, the magnetic article proximity detector comprising:

a magnetic field sensor for providing an output signal proportional to a magnetic field;

a detection circuit to detect at least one of;

(a) a parameter of the environment in which the magnetic article is disposed;

(b) a parameter of the environment in which the magnetic article proximity detector is disposed;

(c) a parameter related to a relationship between the magnetic article proximity detector and the magnetic article; and

(d) a parameter of the magnetic article; and

an output control circuit coupled to receive one or more signals from said detection circuit, and in response to the one or more signals for providing a data string in accordance with a predetermined protocol in which a first logic data bit having a first logic value in the data string is provided from a first single pulse having a first pulse characteristic and a second logic data bit having a second different logic value in the data string is provided from a second single pulse having a second different pulse characteristic, wherein the second different pulse characteristic is multiple of the first pulse characteristic.

2. The detector of claim 1 wherein said detection circuit comprises at least one of:

a speed detection circuit coupled to said magnetic field sensor and said output control circuit;

a direction detection circuit coupled to said magnetic field sensor and said output control circuit;

a temperature detection circuit having an output coupled to said magnetic field sensor and said output control circuit;

an air gap detection circuit coupled said magnetic field sensor and said output control circuit; and

a voltage detection circuit coupled said magnetic field sensor and said output control circuit.

3. The detector of claim 2 wherein said direction detection circuit is coupled to said magnetic field sensing circuit through said speed detection circuit.

4. The detector of claim 2 further comprising an automatic gain control (AGC) circuit coupled between said magnetic field sensor and said speed detection circuit.

5. The detector of claim 4 further comprising an offset adjustment circuit coupled between said magnetic field sensor and said AGC circuit.

6. The detector of claim 1 wherein said magnetic field sensor comprises:

a first Hall effect sensor;

a second Hall effect sensor disposed a distance away from said first Hall effect sensor;

a magnet having a first pole disposed near said first and second Hall effect sensors and a second pole displaced from said first and second Hall effect sensors; and

an amplifier circuit coupled to receive outputs from said first and second Hall effect sensors and for providing an amplified output signal at the output of said magnetic field sensor.

7. The detector of claim 1 wherein:

the first logic data bit corresponds to a logic zero;

the second logic data bit corresponds to a logic one; and

wherein said data string includes a start data sequence (SDS) and at least one data word containing diagnostic information.

8. The detector of claim 7 wherein said at least one data word is comprised of two data logic bits.

9. The detector of claim 7 wherein said at least one data word is comprised of three or more data logic bits.

10. The detector of claim 7 wherein said at least one data word represents at least one condition related to one of:

(a) air gap out of range;

(b) air gap close to out of range;

(c) air gap less than nominal but not close to out of range;

(d) air gap greater than a nominal value;

(e) temperature less than a first predetermined low threshold temperature;

(f) temperature greater than a second predetermined high threshold temperature; and

(g) temperature between first predetermined low threshold temperature and second high predetermined threshold temperature.

11. The detector of claim 1 wherein, in response to a target moving in a first direction, said output control circuit provides a first data string which includes diagnostic information.

12. The detector of claim 11 wherein, in response to the target moving in a second different direction, said output control circuit provides a second data string which does not include diagnostic information.

13. The detector of claim 11 wherein, in response to the target moving in a second different direction, said output control circuit provides a second data string which includes diagnostic information.

14. The detector of claim 1 wherein the pulse characteristic corresponds to one of:

a. a pulse width characteristic;

b. a pulse current level characteristic; and

c. a pulse voltage level characteristic.

15. The detector of claim 14 wherein:

a first current level corresponds to a first logic value;

a second current level corresponds to a second different logic value; and

a third current level corresponds to direction information.

16. The detector of claim 1 wherein the protocol is provided in voltage format.

17. The detector of claim 1 wherein said magnetic field sensor comprises at least three Hall elements arranged in a row, each Hall element spaced apart from an adjacent Hall element by a predetermined distance and wherein in a first pair of Hall elements generate a first differential signal and a second pair of Hall elements generate a second differential signal.

18. The detector of claim 17 wherein the first pair of Hall elements correspond to a left Hall element and a middle Hall element and the first differential signal corresponds to a left channel.

19. The detector of claim 18 wherein the second pair of Hall elements correspond to a right Hall element and a middle Hall element and the second differential signal corresponds to a right channel.

20. The detector of claim 19 wherein both the left and right channels are adapted to provide speed information, and output signals from both the left and right channels are provided to the direction detection circuit which examines a phase relationship between the output signal of the left channel and the output signal of the right channel to determine a direction in which the magnetic article is moving with respect to the magnetic article proximity detector.

21. A magnetic article proximity detector for detecting a magnetic article, the magnetic article proximity detector comprising:

a magnetic field sensor for providing an output signal proportional to a magnetic field;

a detection circuit to detect at least one of;

(a) a parameter of the environment in which the magnetic article is disposed;

(b) a parameter of the environment in which the magnetic article proximity detector is disposed;

(c) a parameter related to a relationship between the magnetic article proximity detector and the magnetic article; and

(d) a parameter of the magnetic article; and

an output control circuit coupled to receive one or more signals from said detection circuit, and in response to the one or more signals for providing a data string in accordance with a predetermined protocol in which a first logic data bit having a first logic value in the data string is provided from a first single pulse having a first pulse width and a second logic data bit having a second different logic value in the data string is provided from a second single pulse having a second different pulse width.

22. The detector of claim 21, wherein the second different pulse width is a multiple of the first pulse width.