HK1170327A - System and method used for an electronic article surveillance system and security system - Google Patents

Description

System and method for electronic article surveillance system and security system

Technical Field

The present invention relates generally to a method and system for reducing false alarm signals in electronic theft detection systems, and more particularly, to a method and system for detecting interference levels between electronic article surveillance ("EAS") systems and metal detection systems, and adjusting sensitivity levels to minimize false alarm trigger signals.

Background

Electronic article surveillance ("EAS") systems are detection systems that are capable of detecting markers or tags in a given detection area. EAS systems have a variety of uses. Most of the time, EAS systems are used as security systems for preventing theft in stores or removal of property from office buildings. EAS systems have been variously formed and employ various technologies.

A typical EAS system includes an electronic detection EAS unit, a marker and/or tag, and a detacher or deactivator. The detection unit includes a transmitter antenna and a receiver antenna and is used to bring any activated tags or labels within range of the detection unit. For example, the antenna portion of the detection unit may be latched to the ground as a pedestal, buried in the floor, mounted on a wall, or hung from a ceiling. The detection units are typically placed in areas of heavy traffic, such as entrances and exits of stores or office buildings. The deactivator sends a signal to detect and/or deactivate the tag.

The markers and/or tags have special features and are specifically designed to be attached to or embedded in goods or other objects to be protected. When the activated flag passes the detection unit, an alarm is sounded, a light is turned on, and/or some other suitable control device is configured to indicate removal of the flag from the prohibited detection area covered by the detection unit.

Most EAS systems operate using the same general principles. The detection unit comprises one or more transmitters and receivers. The transmitter transmits signals across the detection zone at a defined frequency. For example, at a retail store, transmitters and receivers are placed on opposite sides of a check out aisle or exit, thereby forming a detection zone. When the tag enters the area, it interferes with the signal sent by the transmitter. For example, the tag may alter the signal emitted by the transmitter by using a simple semiconductor junction, a modulation circuit consisting of an inductor and a capacitor, a soft magnetic tape or wire, or an oscillating resonator. The flag may also change the signal by repeating the signal for a period of time after the transmitter terminates the signal transmission. The receiver then detects this interference caused by the marker by receiving a signal having the desired frequency, receiving the signal at the desired time, or a combination of both. As an alternative to the basic design described above, the receiver and transmitter units (including their respective antennas) may be mounted in a single housing.

Magnetic materials or metals (e.g., metal shopping baskets) placed near the EAS marker or transmitter may interfere with the optimal performance of the EAS system. Also, some unscrupulous individuals utilize EAS shields (e.g., gold foil lined bags) in an attempt to steal merchandise from the store without detection by any EAS system. The metal lining of these bags may shield the tagged items from the EAS system by preventing interrogation signals from reaching the tags or by preventing reply signals from reaching the EAS system. When the shielded markers pass through the detection unit, the EAS system cannot detect the markers. Thus, the store thief can remove the item from the store without activating the alarm.

Metal detection systems are used in conjunction with EAS systems to detect the presence of metal objects such as gold foil lined bags. The metal detection system may use a transmitter and receiver common to EAS systems. For metal detection, the transmitter emits a signal across the detection zone at a predetermined metal detection frequency. When a metal object enters the detection area, interference occurs with the signal emitted by the transmitter. The receiver then detects the interference generated by the metal object by receiving the modified signal. Once the modified signal is detected, an alarm is sounded, a light is turned on, and/or some other suitable control device is set to indicate removal of the flag from the prohibited detection zone covered by the detection unit.

The EAS system and the metal detection system operate at different excitation frequencies to prevent interference between the systems. For example, EAS systems and metal detection systems may use operating frequencies that differ by 5 kHz. For various reasons, the operating frequencies of these systems may shift, causing signal interference. Conventional metal detection systems do not effectively address the interference problem. Thus, conventional metal detection systems are prone to generating false alarm signals. There is a need for a system and method for detecting interference levels between electronic article surveillance ("EAS") systems and metal detection systems and adjusting sensitivity levels for false alarm trigger signals.

Disclosure of Invention

The present invention advantageously provides a method and system for adjusting the threshold for alarm event triggering based on the detected interference level. The system comprises: a discrepancy calculating module that calculates a discrepancy value according to a difference between a maximum value and a minimum value of the discrepancy values using a plurality of sampling values. A comparison module is provided to compare the discrepancy value with a predetermined interference threshold and to generate an activation signal. A fast threshold adjustment module receives the activation signal when the discrepancy value is greater than or equal to the predetermined interference threshold; a slow threshold adjustment module receives the activation signal when the discrepancy value is less than the predetermined interference threshold. The excitation signal triggers an output from the fast threshold adjustment module or the slow threshold adjustment module, which is used to adjust the threshold.

According to one embodiment, a method for adjusting a threshold for alarm event triggering as a function of a detected interference level may comprise: receiving a plurality of sampling values; and calculating a disparity value according to a difference value between a maximum value and a minimum value of the plurality of disparity values. The discrepancy value is compared to a predetermined interference threshold and an activation signal is generated. Providing an activation signal to a fast threshold adjuster when the discrepancy value is greater than the predetermined interference threshold value and providing the activation signal to a slow threshold adjuster when the discrepancy value is less than the predetermined interference threshold value. The activation signal triggers an output from one of the fast threshold adjuster and the slow threshold adjuster, the threshold being adjusted in accordance with the output from either the fast threshold adjuster or the slow threshold adjuster.

According to another embodiment, the present invention provides a security system for adjusting the threshold of alarm event triggering based on the detected interference level. The security system includes: an antenna, an electronic article surveillance system that utilizes the antenna to detect the presence of an activation marker, and a metal detection system that utilizes the antenna to detect a metal object. The metal detection system includes: a discrepancy calculating module that calculates a discrepancy value according to a difference between a maximum value and a minimum value of the discrepancy values using a plurality of sampling values. A comparison module compares the discrepancy value to a predetermined interference threshold and generates an activation signal. The metal detection system includes a fast threshold adjustment module that receives the excitation signal when the discrepancy value is greater than or equal to the predetermined interference threshold value; and a slow threshold adjustment module that receives the activation signal when the discrepancy value is less than the predetermined interference threshold, 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.

Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

Drawings

The full scope of the invention, together with the attendant advantages and features thereof, will be best understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a block diagram of an exemplary security system having EAS detection capability and metal detection capability constructed in accordance with the principles of the present invention;

FIG. 2 is an exemplary diagram of an interference detector and threshold adjustment circuit according to the principles of the present invention;

FIG. 3 is another exemplary diagram of an interference detector and threshold adjustment circuit according to the principles of the present invention;

FIG. 4 is a waveform diagram during a time slot when no interference is detected between the EAS system and the metal detection system;

FIG. 5 is a waveform diagram during a time slot when interference is detected between an EAS system and a metal detection system;

fig. 6 is an enlarged waveform diagram of the diagram of fig. 5.

Detailed Description

Before describing in detail exemplary embodiments that are in accordance with the present invention, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to implementing a system and method for detecting a level of interference between an electronic article surveillance ("EAS") system and a metal detection system and adjusting thresholds to reduce false alarm signals.

The system and method components have been represented where appropriate by conventional numbers in the drawings. The accompanying drawings show specific details for the purpose of understanding only embodiments of the invention, and so will be readily apparent to those skilled in the art having the benefit of this description.

As used herein, relational terms, such as "first" and "second," "top" and "bottom," and the like, may be used solely to distinguish one entity or component from another entity or component without necessarily requiring or implying any physical or logical relationship or order between such entities or components.

One embodiment of the present invention advantageously provides a method and system for detecting interference levels between electronic article surveillance ("EAS") systems and metal detection systems, and adjusting thresholds to minimize false alarm triggers.

The EAS system detects markers that pass through a predetermined detection zone (also referred to as an interrogation zone). The markers may include fused cast amorphous tape strips, as well as other marker types. Under certain magnetic bias conditions, the markers receive and store energy at their natural resonant frequency, such as acousto-magnetic (acousto-magnetic) field energy. When the transmitted energy source is turned off, the marker becomes the source of the signal and radiates energy, such as acousto-magnetic ("AM") energy, at its resonant frequency. The EAS system is configured to detect AM energy transmitted by the marker in addition to other energy.

One embodiment of the present invention advantageously provides a method and system for detecting the presence of metal in the interrogation zone of a security system and determining whether the detected metal is an EAS metal shield such as a gold foil lined bag. The security system combines traditional EAS detection capabilities with metal detection to improve system accuracy, thereby reducing the likelihood of false alarms.

Referring now to the drawings in which like reference designators refer to like elements, there is shown in FIG. 1 a security system constructed in accordance with the principles of the present invention and designated generally as "100". The security system 100 may be located at a venue entrance, among other locations. The security system 100 may include an EAS system 102, a metal detection system 104, and a pair of pedestals 106a, 106b (collectively pedestals 106) on opposite sides of, for example, an entrance 108. The metal detection system may include an interference detector and threshold adjustment circuit 105. One or more antennas 107a, 107n (collectively antennas 107) may be included in pedestals 106 that are spaced apart by a known distance for use by the EAS system 102 and the metal detection system 104. A system controller 110 is provided for controlling the operation of the security system 100 and is electrically coupled to the EAS system 102, the metal detection system 104, and the antenna 107, among other components. Note that while fig. 1 shows the interference detector and threshold adjustment circuit 105 as part of the metal detection system 104, the interference detector and threshold adjustment circuit 105 may be separate or included in other components of the system 100, such as part of the system controller 110. Also, although the EAS system 102, the metal detection system 104, and the system controller 110 are shown as separate components, such representation is for ease of understanding and is not intended to limit the scope of the present invention. It is understood that the EAS system 102, the metal detection system 104, and the system controller 110 may be incorporated into fewer than 3 housings.

According to one embodiment, the EAS system 102 employs transmission bursts and listening devices to detect objects such as markers. The detection period may be 90Hz (11.1 milliseconds) or other detection period. The detection cycle may include four time periods including a transmission window, a tag detection window, a synchronization window, and a noise window. The transmission window may be defined as a time period "a". During time period A, the EAS system 102 may transmit a 1.6 millisecond burst of AM field at 58kHz, thereby exciting and interrogating markers that are within transmitter and range and resonating at the same frequency. The sign may receive and store a sufficient amount of energy to become an energy/signal source. Once energized, the marker may generate an AM field at 58kHz until the energy storage gradually dissipates in a process known as ringing (ringdown).

The tag detection window may be defined as a time period "B". The tag detection window may follow directly after the transmission window in time and may last 3.9 milliseconds (to 5.5 milliseconds). During time period B, the flag transmits a signal while the system is idle (e.g., while the system is not transmitting a signal). Time period B is defined by a quiet background level because the EAS system 102 is not transmitting a signal. Typically, the amplitude of the AM field signal for the EAS system 102 is several orders of magnitude greater than the amplitude of the AM field signal for the marker. Without the EAS system 102 transmitting an AM field signal, the receiver is better able to detect the signal transmission from the marker.

The synchronization window may be defined as a time period "C". The synchronization window may follow directly in time after the tag detection window and may last for 1.6 milliseconds (to 7.1 milliseconds). The synchronization window allows the signal environment to become stable after the tag detection window. Further, the noise window is defined as a time period "D". The noise window may follow directly in time after the synchronization window and may last 4.0 milliseconds (to 11.1 milliseconds). During the noise window, the desired communication environment is devoid of interrogation and response signals so that the noise component of the communication environment can be measured. The noise window gives the receiver additional time to listen for the tag signal. The energy in the marker may dissipate completely during time period D, whereby the receiver may not be able to detect the AM signal emitted from the marker. Any AM signal detected during this time period is due to an unknown interference source. To this end, the alarm trigger signal may be disabled during the time period D.

According to one embodiment, a metal detection system 104 is provided that shares hardware components with the EAS system 102. Thus, the metal detection system 104 may share an antenna 107 with the EAS system 102. For example, the antenna 107 may be employed as a transmitting antenna for the EAS system 102 and the metal detection system 104. The metal detection system 104 may monitor signals for induced eddy currents that indicate the presence of a metal object in the vicinity of the antenna 107. Typically, for a good conductor, the induced eddy currents dissipate in about a few microseconds. By comparison, eddy currents dissipate nearly two orders of magnitude faster than acoustic (acoustic) tagged AM energy.

The EAS system 102 and the metal detection system 104 may be designed to operate at different frequencies. For example, the EAS system 102 may operate at 58kHz, while the metal detection system 104 may operate at 56 kHz. One of ordinary skill in the art will readily appreciate that these systems may operate at other frequencies. To avoid mutual interference during operation, the signals generated by the EAS system 102 and the metal detection system 104 are separated by at least a detection time period (e.g., 1/90Hz or greater).

However, if one or both of the EAS system 102 and the metal detection system 104 experience a phase shift during operation that reduces their signal separation below the detection period, the systems will experience mutual interference. For example, the EAS system 102 or the metal detection system 104 may be phase shifted to operate at a lower noise period, among other reasons.

Fig. 2 is a diagram of a first exemplary jammer detector and threshold adjustment circuit 105. The threshold module 205 is in communication with the antenna 107 to receive and process signals transmitted from nearby objects. The threshold module 205 selects a threshold adjustment speed based on a comparison between the calculated discrepancy value and a predetermined interference threshold value. The threshold module 205 may include a sampling module 207, a difference calculation module 209, and a comparison module 211.

The sampling module 207 extracts a predetermined number of samples transmitted from the antenna 201. The sampled values may represent the signal strength or some other measurable characteristic of the received signal. For example, the sampling module 207 may operate at a frequency of 46.296kHz and may extract sixteen (16) samples representing signal strength. One of ordinary skill in the art will readily appreciate that the sampling module 207 may operate at other frequencies and may extract other numbers of sample values. The difference calculation module 209 receives a predetermined number of sample values from the sampling module 207 and determines a value (including a maximum value and a minimum value) for each sample from the received sample values. The difference calculation module 209 calculates a difference value or difference value between the maximum value and the minimum value. According to one embodiment, the discrepancy calculating module 209 may calculate a real-time continuous discrepancy value. The comparison module 211 receives the calculated discrepancy value from the discrepancy calculating module 209 and compares the discrepancy value to a predetermined interference threshold value.

If the comparison module 211 determines that the discrepancy value is greater than or equal to the predetermined interference threshold value, the comparison module 211 selects the fast threshold adjustment module 215. For example, the fast threshold adjustment module 215 may be a 200 tap Low Pass Filter (LPF) or other fast tap LPF. Alternatively, if the comparison module 211 determines that the discrepancy value is less than the predetermined interference threshold, the comparison module 211 selects the slow threshold adjustment module 217. For example, the slow threshold adjustment module 217 may be an 800 tap LPF or other slow tap LPF. One of ordinary skill in the art will readily appreciate that a greater number of threshold adjustment modules may be provided to improve the speed control granularity.

The jammer detector and threshold adjustment circuit 105 may include a reduction module 220, the reduction module 220 receiving a plurality of sample values from the sampling module 207 and providing a single value to the fast threshold adjustment module 215 and the slow threshold adjustment module 217. The reduction module 220 may include a normalization module 221 and a processing module 223. The normalization module 221 receives a plurality of sample values from the sampling module 207 and normalizes the sample values. For example, the normalization module 221 may calculate an average value from the plurality of sample values received from the sampling module 207. The processing module 223 receives the calculated average from the normalization module 221 and performs data reduction to convert the plurality of sample values to a single sample value. The processing module 223 provides the single sample value to the fast threshold adjustment module 215 and the slow threshold adjustment module 217.

As described above, the comparison module 211 selects either the fast threshold adjustment module 215 or the slow threshold adjustment module 217 to process the single sample value provided by the processing module 223. If the fast threshold adjustment module 215 is selected, the 200 tap LPF performs an average of the single sample value with 199 previously stored single sample values. Alternatively, if the slow threshold adjustment module 215 is selected, the 800 tap LPF performs an average of the single sample value and 799 previously stored single sample values. According to one embodiment, both the 200 tap LPF and the 800 tap LPF store each single sample value even if the LPF is not selected to process the single sample value.

The results from the respective n-tap LPFs are provided to a summing module 230. According to one embodiment, the summing module 230 also receives a hard threshold provided by a hard threshold module 232, such as a non-volatile memory. The hard threshold module 232 may include a table of values for adjusting the sensitivity of the interference detector and threshold adjustment circuit 105. According to one embodiment, the summing module 230 calculates a final threshold value that is stored in a final threshold module 234.

In accordance with another embodiment of the present invention, fig. 3 is a block diagram of the second exemplary interference detector and threshold adjustment circuit 105 having components that provide a percentage of the calculated discrepancy value to calculate the final threshold value stored in the final threshold module 234. The jammer detector and threshold adjustment circuit 105 adjusts the final threshold based on the real-time jammer data.

The threshold adjustment circuit 105 of fig. 3 includes a soft threshold module 302, which soft threshold module 302 receives the discrepancy value from the discrepancy calculating module 209 and calculates a percentage of the discrepancy value or a soft threshold. For example, the soft threshold module 302 may calculate the soft threshold as 10% of the discrepancy value received from the discrepancy calculating module 209. One of ordinary skill in the art will readily appreciate that other percentages may be selected for the soft threshold.

The soft threshold module 302 is configured to receive a signal from the comparison module 211 when the calculated difference is greater than or equal to a predetermined interference threshold. If the comparison module 211 determines that the calculated difference is less than the predetermined interference threshold, then no signal is provided to the soft threshold module 302. Upon receiving the signal from the comparison module 211, the soft threshold module 302 releases the soft threshold to the summing module 230. According to one embodiment, the summing module 230 sums a soft threshold, a hard threshold provided by a hard threshold module 232, such as a non-volatile memory, and the results from the corresponding n-tap LPF. The summing module 230 calculates a final threshold value that is stored in a final threshold module 234. The final threshold module 234 may be coupled to an alarm decision module (not shown) that receives threshold information to determine whether to generate or disable an alarm event.

Fig. 4 is a waveform diagram 400 of two exemplary traces of a signal generated by the metal detection system 104 during a time slot or period when no interference is detected between the EAS system 102 and the metal detection system 104. The upper waveform 402 illustrates a digital signal generated by a microprocessor within the metal detection system 104. The lower waveform 404 illustrates the signal received at the front end of the metal detection system 104. The window 406 defines a time frame or region of interest for analyzing the waveforms 402, 404.

According to one embodiment, and in a time slot or period that does not include interference between the EAS system 102 and the metal detection system 104, the upper waveform 402 includes a first portion 408 in which the microprocessor collects signal samples within the window 406. The signal samples shown include jitter. For example, sixteen samples within the window 406 may be captured from the first portion 408. The upper waveform 402 includes a second portion 409 defined by a pulse waveform representing the amount of time the microprocessor processes the signal sample.

The waveform diagram 400 shows that the lower waveform 404 includes a signal portion 410 within a window 406 that represents a derivation of the sixteen captured samples received at the front end of the metal detection system 104. The signal portion 410 is composed of a flat line DC signal (e.g., no interference induced fluctuations). The lower waveform 404 includes a ringing portion 411 for the rectified transmit pulse. One of ordinary skill in the art will readily appreciate that any number of samples may be used.

Fig. 5 is a waveform diagram 500 of two exemplary traces of a signal generated by the metal detection system 104 during a time slot or period when interference is present between the EAS system 102 and the metal detection system 104. Specifically, there is a 2kHz interference signal between the EAS system 102 and the metal detection system 104. The upper waveform 502 illustrates a digital signal generated by a microprocessor within the metal detection system 104. The lower waveform 504 illustrates the signal received at the front end of the metal detection system 104. The window 506 defines a time frame or region of interest for analyzing the waveforms 502, 504.

According to one embodiment, and in a time slot or period that includes interference between the EAS system 102 and the metal detection system 104, the upper waveform 502 includes a first portion 508 in which the microprocessor collects signal samples within a window 506. For example, sixteen samples within the window 506 may be captured from the first portion 508. The upper waveform 502 includes a second portion 409 defined by a pulse waveform that represents the amount of time the microprocessor processes the signal sample.

Waveform diagram 500 shows that lower waveform 504 includes a signal portion 510 within window 506 that represents a derivative of the sixteen captured samples received at the front end of metal detection system 104. The signal section 510 is defined by a DC signal comprising a superimposed 2kHz modulated sine wave interference signal. The lower waveform 504 includes a ringing portion 511 for the rectified transmit pulse. One of ordinary skill in the art will readily appreciate that any number of samples may be employed, or that any signal frequency may cause interference. Once interference is detected, the threshold is adjusted using a faster averaging filter than without interference. The fast threshold adjustment enables the metal detection system 104 to track noise signals, thereby minimizing false alarm triggers generated during severe fluctuations in interference levels. For example, the metal detection system 104 may detect periods of severe fluctuation in the interference level when a metal object is in the vicinity of the antenna 107.

Fig. 6 is a waveform diagram 600 of an enlarged view of the waveform diagram 500 of fig. 5. The upper waveform 502 illustrates a digital signal generated by a microprocessor within the metal detection system 104. The first portion 508 is shown within the window 506, thereby having a jitter of a magnitude comparable to that of the digital pulse. The lower waveform 504 shows a signal portion 510 within the window 506 that represents a derivative of the sixteen captured samples received at the front end of the metal detection system 104. The signal portion 510 shown within the window 506 includes a DC signal superimposed with a 2kHz modulated sine wave. A flag 602 is placed within the window 506 to identify the maximum sample value. A marker 604 is placed within the window 506 to identify the minimum sample value. According to one embodiment, the discrepancy calculating module 209 calculates a discrepancy value by determining the difference between the maximum value associated with the flag 602 and the minimum value associated with the flag 604.

The present invention can be realized in hardware, software, or a combination of hardware and software. Any kind of computing system, or device adapted for carrying out the methods described herein, may be adapted to perform the functions described herein.

A typical combination of hardware and software could be a specialized computer system having one or more processing elements and a computer program stored on a storage medium that, when loaded and executed, controls the computer system such that it carries out the methods described herein. The present invention can also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which, when loaded in a computer system is able to carry out these methods. Storage medium refers to any volatile or non-volatile storage device.

A computer program or application in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a computer system having an information processing capability to perform a particular function either directly or after either or both of a) conversion to another language, code or notation, and b) reproduction in another material form.

Moreover, unless indicated to the contrary in the foregoing, it should be noted that all of the accompanying drawings are not to scale. It will be apparent that the invention can be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

Claims (20)

1. A system for an electronic article surveillance system that adjusts thresholds for alarm event triggering based on detected interference levels, comprising:

a difference calculation module that calculates a difference value according to a difference value between a maximum value and a minimum value of a plurality of sample values using the plurality of sample values;

a comparison module that compares the discrepancy value to a predetermined interference threshold and generates an activation signal;

a fast threshold adjustment module that receives the activation signal when the discrepancy value is at least equal to the predetermined interference threshold value; and

a slow threshold adjustment module that receives the activation signal when the discrepancy value is less than the predetermined interference threshold, 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.

2. The system of claim 1, further comprising:

a normalization module that receives the plurality of sample values and calculates a normalized value for the plurality of sample values; and

a processing module in communication with the normalization module, the processing module employing the normalization value to represent a single sample value.

3. The system of 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 of claim 3, wherein the fast threshold adjustment module comprises a 200-tap low pass filter and the slow threshold adjustment module comprises an 800-tap low pass filter.

5. The system of 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; 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 of claim 5, further comprising: a summing module that sums a hard threshold and an output from one of the fast threshold adjustment module and the slow threshold adjustment module.

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

8. The system of claim 7, further comprising: a summing module that sums a hard threshold, the soft threshold, and an output from one of the fast threshold adjustment module and the slow threshold adjustment module.

9. A method for an electronic article surveillance system that adjusts a threshold for alarm event triggering based on a detected interference level, the method comprising:

receiving a plurality of sampling values;

calculating a difference value according to a difference value between a maximum value and a minimum value of the plurality of sampling values;

comparing the discrepancy value to a predetermined interference threshold value;

providing an activation signal to a fast threshold adjuster when the discrepancy value is at least equal to the predetermined interference threshold value; and

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

generating an output from one of the fast threshold adjuster and the slow threshold adjuster triggered by the excitation signal; and

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

10. The method of claim 9, further comprising:

calculating a mean value for the plurality of sample values; and

the average is used to generate a representative single sample value.

11. The method of claim 10, further comprising: providing the single sample value to the fast threshold adjuster and the slow threshold adjuster.

12. The method of claim 11, further comprising: a 200-tap low-pass filter is provided for the fast threshold adjuster and an 800-tap low-pass filter is provided for the slow threshold adjuster.

13. The method of claim 12, further comprising:

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

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

providing an output to the 200-tap low pass filter;

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

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

an output is provided for the 800 tap low pass filter.

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

15. The method of claim 14, further comprising: the soft threshold is calculated as a percentage of the difference value.

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

17. A security system for an electronic article surveillance system for adjusting a threshold for alarm event triggering based on a detected interference level, the security system comprising:

an antenna;

an electronic article surveillance system that utilizes the antenna to detect the presence of an activation flag;

a metal detection system that utilizes the antenna to detect a metal object, the metal detection system comprising:

a difference calculation module that calculates a difference value according to a difference value between a maximum value and a minimum value of a plurality of sample values using the plurality of sample values;

a comparison module that compares the discrepancy value to a predetermined interference threshold and generates an activation signal;

a fast threshold adjustment module that receives the activation signal when the discrepancy value is at least equal to the predetermined interference threshold value; and

a slow threshold adjustment module that receives the activation signal when the discrepancy value is less than the predetermined interference threshold, 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.

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

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

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

a normalization module that receives the plurality of sample values and calculates a mean for the plurality of sample values; and

a processing module in communication with the normalization module, the processing module employing the calculated mean to represent a single sample value 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.