Magnetic thread reader

1. A method of identifying a coded magnetic thread comprising generating a digital representation of the thread and comparing the digital representation with one or more known digital representations characterised in that the method further comprises scanning the digital representation to locate a predetermined code sequence; rotating the digital representation to locate the predetermined code sequence in a predetermined position corresponding to the position of the predetermined code sequence in a stored version of the or each known digital representation prior to carrying out the comparison step.

2. A method according to claim 1 , wherein the digital representation is binary.

3. A method according to claim 2 , wherein prior to performing the comparison, the digital representation is scanned for at least one feature which indicates the likelihood that the digital representation is valid.

4. A method according to claim 3 , wherein the digital representation is scanned to confirm that the least significant and most significant bits are set.

5. A method according to claim 3 , wherein the digital representation is scanned to confirm that the number of bit changes are within predefined limits.

6. A method according to claim 3 , wherein the digital representation is scanned to confirm that the number of bits set are within predefined limits.

7. A method according to claim 3 , wherein the digital representation is scanned to confirm that the predetermined code sequence is present and in the correct location.

8. A method according to claim 3 , wherein the digital representation is scanned to confirm that the code is asymmetric.

9. A method according to claim 3 , wherein different scores are applied to different features depending on their relative importance.

10. A method according to claim 1 , wherein the code is asymmetric.

11. A method according to claim 10 , wherein the comparison is performed against reversed versions of the known digital representations, thereby determining the orientation of the coded magnetic thread.

12. A method according to claim 11 , wherein the lateral displacement of the thread is measured and used to determine which face of a sheet document containing the thread is uppermost.

13. A method according to claim 11 , wherein the relative displacement of the thread from a known magnetic feature is measured and used to determine which face of a sheet document containing the thread and magnetic feature is uppermost.

14. Apparatus for identifying a coded magnetic thread comprising a magnetic field detector, a processing system for processing signals generated by the detector to generate a digital representation of the thread and for comparing the digital representation with one or more known digital representations characterised in that the processing system is further adapted to scan the digital representation to locate a predetermined code sequence; and to rotate the digital representation to locate the predetermined code sequence in a predetermined position corresponding to the position of the predetermined code sequence in a stored version of the or each known digital representation prior to comparing the digital representation with the known digital representations.

15. Apparatus according to claim 14 , wherein the processing system is further adapted to compare the digital representation against reversed versions of the known digital representations, thereby determining the orientation of the coded magnetic thread.

16. Apparatus according to claim 14 , wherein the apparatus further comprises a detector for measuring the lateral displacement of the thread for determining which face of a sheet document containing the thread is uppermost.

17. Apparatus according to claim 14 , wherein the processing system is further configured to scan the digital representation for features which indicate the likelihood of the digital representation being valid, prior to performing the comparison.

18. Apparatus according to claim 14 for carrying out a method of identifying a coded magnetic thread comprising generating a digital representation of the thread and comparing the digital representation with one or more known digital representations characterised in that the method further comprises scanning the digital representation to locate a predetermined code sequence; rotating the digital representation to locate the predetermined code sequence in a predetermined position corresponding to the position of the predetermined code sequence in a stored version of the or each known digital representation prior to carrying out the comparison step.