Interference detector resulting in threshold adjustment

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.

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.