Interference detector resulting in threshold adjustment

1. A system for adjusting a threshold value of an alarm event trigger based on a detected interference level, the system comprising:

a discrepancy calculating module, the discrepancy calculating module using a plurality of sample values to calculate a discrepancy value based on a difference between a maximum value and a minimum value of the plurality of sample values;

a comparing module, the comparing module comparing the discrepancy value to a predefined interference threshold value and generating an activation signal;

a fast threshold adjustment module, the fast threshold module receiving the activation signal when the discrepancy value is at least equal to the predefined interference threshold value; and

a slow threshold adjustment module, the slow threshold adjustment module receiving the activation signal when the discrepancy value is less than the predefined interference threshold value, the activation signal triggering an output from one of the fast threshold adjustment module and the slow threshold adjustment module, the output being used to adjust the threshold value.

2. The system according to claim 1 , further comprising:

a normalizing module, the normalizing module receiving the plurality of sample values and calculating a normalized value for the plurality of sample values; and

a processing module in communication with the normalizing module, the processing module using the normalized value to represent a single sample value.

3. The system according to claim 2 , wherein the processing module provides the single sample value to the fast threshold adjustment module and the slow threshold adjustment module.

4. The system according to claim 3 , wherein the fast threshold adjustment module includes a 200 tap low pass filter and the slow threshold adjustment module includes an 800 tap low pass filter.

5. The system according to claim 4 , wherein the 200 tap low pass filter stores 200 previous sample values and averages the single sample value with the stored 200 previous sample values and the 800 tap low pass filter stores 800 previous sample values and averages the single sample value with the stored 800 previous sample values.

6. The system according to claim 5 , further comprising a summing module that adds a hard threshold value and the output from one of the fast threshold adjustment module and the slow threshold adjustment module.

7. The system according to claim 1 , further comprising a soft threshold module that calculates a soft threshold value based on a percentage of the discrepancy value.

8. The system according to claim 7 , further comprising a summing module that adds the soft threshold value, a hard threshold value and the output from one of the fast threshold adjustment module and the slow threshold adjustment module.

9. A method for adjusting a threshold value of an alarm event trigger based on a detected interference level, the method comprising:

receiving a plurality of sample values;

calculating a discrepancy value based on a difference between a maximum value and a minimum value of the plurality of sample values;

comparing the discrepancy value to a predefined interference threshold value;

providing an activation signal to a fast threshold adjustor when the discrepancy value is at least equal to the predefined interference threshold value;

providing the activation signal to a slow threshold adjustor when the discrepancy value is less than the predefined interference threshold value;

generating an output from one of the fast threshold adjustor and the slow threshold adjustor that is triggered by the activation signal; and

adjusting the threshold value based on the output from one of the fast threshold adjustor and the slow threshold adjustor.

10. The method according to claim 9 , further comprising:

calculating an average for the plurality of sample values; and

applying the average to generate a representative single sample value.

11. The method according to claim 10 , further comprising providing the single sample value to the fast threshold adjustor and the slow threshold adjustor.

12. The method according to claim 11 , further comprising providing a 200 tap low pass filter for the fast threshold adjustor and providing an 800 tap low pass filter for the slow threshold adjustor.

13. The method according to claim 12 , further comprising:

storing 200 previous sample values in the 200 tap low pass filter;

averaging the single sample value and the stored 200 previous sample values;

providing an output for the 200 tap low pass filter;

storing 800 previous sample values in the 800 tap low pass filter;

averaging the single sample value and the stored 800 previous sample values; and

providing an output for the 800 tap low pass filter.

14. The method according to claim 13 , further comprising adding a hard threshold value and one of the output for the 200 tap low pass filter and the output for the 800 tap low pass filter.

15. The method according to claim 9 , further comprising calculating a soft threshold value based on a percentage of the discrepancy value.

16. The method according to claim 15 , further comprising adding the soft threshold value, a hard threshold value and one of the output for the 200 tap low pass filter and the output for the 800 tap low pass filter.

17. A security system for adjusting a threshold value of an alarm event trigger based on a detected interference level, the security system comprising:

an antenna;

an electronic surveillance system, the electronic surveillance system using the antenna to detect the presence of active markers;

a metal detection system, the metal detection system using the antenna to detect metal objects, the metal detection system comprising:

a discrepancy calculating module, the discrepancy calculating module using a plurality of sample values to calculate a discrepancy value based on a difference between a maximum value and a minimum value of the plurality of sample values;

a comparing module, the comparing module comparing the discrepancy value to a predefined interference threshold value and generating an activation signal;

a fast threshold adjustment module, the fast threshold adjustment module receiving the activation signal when the discrepancy value is at least equal to the predefined interference threshold value; and

a slow threshold adjustment module, the slow threshold adjustment module receiving the activation signal when the discrepancy value is less than the predefined interference threshold value, the activation signal triggering an output from one of the fast threshold adjustment module and the slow threshold adjustment module, the output being used to adjust the threshold value.

18. The security system according to claim 17 , the metal detection system comprising a soft threshold module that receives the discrepancy value and calculates a soft threshold value based on a percentage of the discrepancy value, the soft threshold module receiving the activation signal when the discrepancy value is greater than or equal to the predefined interference threshold value, the activation signal triggering an output from the soft threshold module, the output being used to adjust the threshold value.

19. The security system according to claim 18 , the metal detection system further comprising a summing module that adds the soft threshold value, a hard threshold value and the output from one of the fast threshold adjustment module and the slow threshold adjustment module.

20. The security system according to claim 17 , the metal detection system further comprising:

a normalizing module, the normalizing module receiving the plurality of sample values and calculating an average for the plurality of sample values;

a processing module, the processing module in communication with the normalizing module, the processing module using the calculated average to represent a single sample value that is derived from the plurality of sample values, the processing module providing the single sample value to the fast threshold adjustment module and the slow threshold adjustment module.