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

• US 7,026,808 B2
• Filed: 09/23/2004
• Issued: 04/11/2006
• 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: Vig, Ravi, Forrest, Glenn, Towne, Jay M.
• Primary Examiner(s): DEB, ANJAN K
• Application Number:
  US10/948,808
• Publication Number:
  US 20050040814A1
• Time in Patent Office: 565 Days
• Field of Search: 324/207.2, 324/165, 324/179, 324/207.18, 324/207.12, 324/677, 341/53, 375/238
• 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 method of providing information about a target having at least a first edge and a second edge, the method comprising:

detecting at least the first and second edges of the target;

generating a pulse in response to each of the detected first and second edges of the target, with each of the pulses having a first or second pulse characteristic with the first pulse characteristic corresponding to a first logic value and the second pulse characteristic corresponding to a second different logic value and wherein a first one of the first and second pulse characteristics is a multiple of a second one of the first and second pulse characteristics; and

forming a data word using at least two pulses wherein the data word conveys a characteristic of at least one of;

(a) the target; and

(b) an environment in which the target is disposed.

2. The method of claim 1 wherein the first pulse characteristic and the second pulse characteristic comprise first and second respective pulse widths and the first pulse width is approximately twice as long as the second pulse width.

3. The method of claim 1 wherein the first logic value corresponds to a logic zero value and the second logic value corresponds to a logic one value.

4. The method of claim 1 wherein the first pulse characteristic comprises a first pulse width and the first pulse width is in the range of about 35 microseconds to about 55 microseconds in length.

5. The method of claim 1 wherein the first pulse characteristic comprises a first pulse width and the first pulse width is in the range of about 65 microseconds to about 110 microseconds in length.

6. The method of claim 1 wherein the first pulse characteristic and the second pulse characteristic comprise first and second respective pulse widths and the first pulse width is in the range of about 35 microseconds to about 55 microseconds in length and the second pulse width is in the range of about 65 microseconds to about 110 microseconds in length.

7. The method of claim 1 wherein the second pulse characteristic comprises a second pulse width and the second pulse width is in the range of about 35 microseconds to about 55 microseconds in length.

8. The method of claim 1 wherein the second pulse characteristic comprises a second pulse width and the second pulse width is in the range of about 65 microseconds to about 110 microseconds in length.

9. The method of claim 1 wherein the first and second pulse characteristics correspond to one of:

a. a pulse width characteristic;

b. a pulse current level characteristic; and

c. a pulse voltage level characteristic.

10. The method of claim 1, wherein said data word conveys a direction of rotation of said target.

11. The method of claim 1, wherein said data word conveys a condition, including at least one of:

(a) an air gap out of range,

(b) an air gap close to out of range,

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

(d) an air gap greater than a nominal value,

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

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

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

12. A method of providing information from a sensor, the method comprising:

detecting a target;

in response to detecting the target, generating a pulse string having one pulse for each edge of the detected target; and

generating a data string from the pulse string with the data string provided from a plurality of logic data bits wherein a first logic data bit is represented by a single pulse having a first pulse characteristic and a second logic data bit is represented by a single pulse having a second pulse characteristic with the second pulse characteristic being approximately twice as long as the first pulse characteristic.

13. The method of claim 12 wherein the data string includes a start data sequence (SDS) and at least one data word containing diagnostic information.

14. The method of claim 13 wherein generating a data string comprises generating a plurality of data words after each SDS.

15. The method of claim 14 wherein generating a data string comprises generating two data bits for each data word.

16. The method of claim 14 further comprising generating a delimiter after each data word.

17. The method of claim 16 wherein generating a delimiter comprises generating a logic zero pulse as a delimiter.

18. The method of claim 12 wherein generating a data string further comprises providing a logic zero data bit having a minimum pulse characteristic defined by an RC time constant coupled to an output of said sensor.

19. The method of claim 12 wherein at least one of said data words represents a diagnostic condition selected from:

air gap out of range, air gap approaching out of range, air gap less than nominal, air gap greater than a nominal value, temperature less than a predetermined low value, temperature greater than a predetermined high value, and temperature between the predetermined low and high values.

20. The method of claim 12 further comprising transmitting only a plurality of logic zero data pulses when a frequency of the detection of the target is above a diagnostic data drop out frequency.

21. The method of claim 12 wherein said generating is performed in response to a target moving proximate to said sensor in a first direction.

22. The method of claim 21 further comprising generating a second pulse string when the target is moving proximate to sensor in a second direction which is different than the first direction.

23. The method of claim 22 wherein said generating a second pulse string comprises generating a pulse for each edge of a detected target wherein each pulse has a duration approximately four times as long as the logic zero data pulse for a detected target moving in the first direction.