Az áruvédelmi antennák üzemeltetésének alapszabályai:
Az antennák rendeltetésszerű használatának szabályai:
Téves riasztást okozhat:
- Minimum 2 méterre kell lennie a vezérlőnek a vevő antennától, a védő távolságon belül számítógép sem lehet.
- Nagy fém tárgyaknak minimum 80 centiméter távolságban kell lenni az antennáktól
- Elektromos kábeleknek a lehető legmesszebb kell lenni.
- Lehetőleg tisztán kell tartani. A portól, nedvességtől az elektronikát óvni kell.
- Nagy méretű fém tárgyakat az antennák elektromágneses mezőjében mozgatnak.
- Elektromágneses antennákból 7 antenna telepíthető egymás mellé (4 adó, 3 vevő), ezt követően 2,5 - 3 m. szünet, majd jöhetnek az újabb antennák.
Rádiófrekvenciás ás akuszto magnetikus rendszereknél több antennát lehet telepíteni.
Amennyiben ezek a feltételek teljesülnek a téves riasztás okai lehetnek:
- mágneses eszközök a címkék közelében
- a vásárlók ruhájában, vagy egyéb magával hozott tárgyaikban nem hatástalanított címke
- zománcozott edények
- hosszú fém tárgyak például: esernyő, létra
Az áruvédelmi antenna nem jelez:
- Szétvagdosott, összegyűrt, vagy az antenna érzékenységének nem megfelelő méretű és/vagy típusú áruvédelmi címkénél.
- Tömör fém tárgyakon csak kiegészítő úgynevezett kemény címkével, vegyesen alkalmazva jelez, ezeken azonban
Az áruvédelmi antennában károsodást okozhat:
- Nagy mértékű feszültség ingadozás
- Az elektronikát belepő por (ezért évente, vagy szükség szerint a port ajánlott kifújni)
- Erőszakos mechanikus behatások
Egyéb angol nylevű anyagok az érdeklődőknek:
Series 304 RF EAS label
These tags are essentially an LC tank circuit that has a resonance peak anywhere from 1.75 MHz to 9.5 MHz. The most popular frequency is 8.2 MHz. Sensing is achieved by sweeping around the resonant frequency and detecting the dip. Deactivation for 8.2 MHz label tags is achieved by detuning the circuit by partially destroying the capacitor. This is done by submitting the tag to a strong electromagnetic field at the resonant frequency which will induce voltages exceeding the capacitor's breakdown voltage, which is artificially reduced by puncturing the tags.
A major concern with these systems is when false alarms occur. A false alarm (or false positive) is when the alarms go off when a person passes through the gate without having stolen any merchandise. This most often is due to tags on merchandise not being properly deactivated but other factors such as bringing in items from other stores, even keyrings can set off the alarm
In some older systems electronic devices have been known to set off alarms. RF systems can react even to a coil of wires (for example, aCat5 cable carried by a forgetful network technician) because stray capacitance forms a LC circuit within the coil itself. It is also possible for alarms to go off without anyone crossing the gates. Such interference is often due to other nearby alarm systems.
EAS (elektronikus áruvédelem) rendszerek általában:
Three types of EAS systems dominate the retail industry. In each case, an EAS tag or label is attached to an item. The tag is then deactivated, or taken from an active state where it will alarm an EAS system to an inactive state where it will not flag the alarm. If the tag is a hard, reusable tag, a detacher is used to remove it when a customer purchases the item it's attached to. If it's a disposable, paper tag, it can be deactivated by swiping it over a pad or with a handheld scanner that "tells" the tag it's been authorized to leave the store. If the item has not been deactivated or detached by the clerk, when it is carried through the gates, an alarm will sound.
RF (Rádió frekvenciás) rendszerek
Radio Frequency (RF) Systems are the most widely used systems in the United States today and RF tags and labels are getting smaller all the time. As you can see in the drawing at the right, the RF EAS system works like this: A label -- basically a miniature, disposable electronic circuit and antenna -- attached to a product responds to a specific frequency emitted by a transmitter antenna (usually one pedestal of the entry/exit gate). The response from the label is then picked up by an adjacent receiver antenna (the other pedestal). This processes the label response signal and will trigger an alarm when it matches specific criteria. The distance between the two gates, or pedestals, can be up to 80 inches wide. Operating frequencies for RF systems generally range from 2 to 10 MHz (millions of cycles per second); this has become standard in many countries. Most of the time, RF systems use a frequency sweep technique in order to deal with different label frequencies.
Sometimes both the transmitter and receiver are combined in one antenna frame -- these are called mono systems and they can apply pulse or continuous sweep techniques or a combination of both. According to Tag Point Ltd. experts, mono systems could be effective for you if your store's entry is small. The mono system is used with hard labels, which are slightly more expensive than paper labels used with RF sweep techniques.
There are many different ways to implement an RF system. The basic idea is that the tag has a helical antenna etched from thin aluminum bonded to a piece of paper. At the end of the antenna is a small diode or RC network that causes the tag to emit a radio signal in response to the radio signal it receives. To disarm the tag, a strong RF pulse (much stronger than the gates emit) blasts the tag and burns out the diode or RC components. Between the gates a burned out tag does not emit a signal, so the gates let it pass without an alarm.
The Electromagnetic (EM) system, which is dominant in Europe, is used by many retail chain stores, supermarkets and libraries around the world. In this technology, a magnetic, iron-containing strip with an adhesive layer is attached to the merchandise. This strip is not removed at checkout -- it's simply deactivated by a scanner that uses a specific highly intense magnetic field. (One of the advantages of the EM strip is that it can be re-activated and used at a low cost.)
What most people refer to as an electromagnetic tag is actually a metal wire or ribbon that has high permeability, making it easy for magnetic signals to flow through it, according to Sensormatic's EAS Product Co. CTO Hap Patterson. "When we drive the tag, flux is being allowed to flow through the tag until it's saturated," he says. "When it's saturated, from a magnetic perspective, it begins to look like air. Saturation occurs abruptly and is an important part of the design of the tag."
Look at the figure showing the EM system with its receive coil and transmitter on either side and tag in the middle. When the tag goes from active to saturated, the receiver detects the change in the amount of the signal picked up from the transmitter. "If you look at the receiver signal, you'll see a bump when saturation occurs," Patterson says. Saturation occurs twice each cycle-once on the transmitter's positive cycle and once on its negative cycle. What is happening is the system is checking for the special material used to make the tag. (In scientific terms, the permeability of steel is much lower than the metal used to make the tag. In addition, when steel goes to saturation, it tends to do so slowly, not abruptly. So the EM system uses these differences to differentiate between a still-active tagged item leaving the store and a wrench in someone's pocket.)
A magnetized piece of semi-hard magnetic material (basically, a weak magnet) is put up next to the active material to deactivate it. When you magnetize the semi-hard material, it saturates the tag and puts it in its inactive saturated state.
That same kind of tag is often used in the library, where it can be reactivated by demagnetizing the semi-hard magnetic material.
The EM system works by applying intensive low frequency magnetic fields generated by the transmitter antenna. When the strip passes through the gate, it will transmit a unique frequency pattern. This pattern is, in turn, being picked up by an adjacent receiver antenna. The small signal is processed and will trigger the alarm when the specific pattern is recognized. Because of the weak response of the strip and the low frequency (typically between 70 Hz and 1 kHz) and intensive field required by the EM system, EM antennas are larger than those used by most other EAS systems, and the maximum distance between entry pedestals is 40 inches. Also, because of the low frequency here, the strips can be directly attached to metal surfaces. That's why EM systems are popular with hardware, book and record stores.
AM - 58 KHZ
The newer acousto-magnetic system, which has the ability to protect wide exits and allows for high-speed label application, uses a transmitter to create a surveillance area where tags and labels are detected. The transmitter sends a radio frequency signal (of about 58 kHz) in pulses, which energize a tag in the surveillance zone. When the pulse ends, the tag responds, emitting a single frequency signal like a tuning fork. While the transmitter is off between pulses, the tag signal is detected by a receiver. A microcomputer checks the tag signal detected by the receiver to ensure it is at the right frequency, is time-synchronized to the transmitter, at the proper level and at the correct repetition rate. If all these criteria are met, the alarm occurs.
AM material is highly magnetostrictive, which means that when you put the tag material in a magnetic field, it physically shrinks. The higher the magnetic field strength the smaller the metal becomes. The metal actually shrinks about one-thousandth of an inch over its full 1.50 inch length.
As a result of driving the tag with a magnetic field, the tag is physically getting smaller and larger. So if it is driven at a mechanically resonant frequency, it works like a tuning fork, absorbing energy and beginning to ring.
This tag also requires bias magnet material in addition to active element material. The active material will shrink no matter which direction the magnetic field is placed upon it. If the tag is driven with Frequency, F, it gets smaller as the magnetic field increases and larger as it's driven towards zero. This means that while it is being driven at F, the tag is trying to work at 2F, because at both positive and negative halves of the drive signal, the tag is getting smaller. To get the tag to work at F, a bias field is required. The bias is provided by a semi-hard magnetic element in the label. When magnetized, the bias prevents the active element from ever being in a zero field condition. So for an entire half of the drive signal, the tag shrinks. Then it expands for the other half. This results in an F response.
When you walk through the gate with a tag, the transmitter in the gate energizes the material and causes it to resonate at F. The transmitter then stops. The tag will continue to "ring" at F for a short period of time, and the receiver listens for that frequency. If it hears it, it knows there is a tag and sounds the alarm.
When the AM tag is demagnetized, it is deactivated. When it's magnetized, it is activated. (This is the opposite of how the deactivation of EM tags works.)
The tags work well when they're close to metal and the stores use metal shopping carts -- not all systems work well with metal objects.)
téves riasztások okai:
It may happen that the
level of disturbances in the place of assembly will be so high that it will worsen system
parameters permanently or temporarily. Always, in such situation, locate the source of
disturbances and try to eliminate it or diminish its impact on the system. If it turns out
impossible, adjust system parameters to diminish the impact of disturbances to the level
allowing correct operation of the system.
6.1. Characteristics of disturbances
Disturbances could be divided into 4 basic types:
1. Permanent disturbances. These disturbances are caused by the elements which,
similarly to securities, form circumference resonate at frequency close to 8.2MHz.
These disturbances can be observed as permanent signals of various shape and
amplitude; they are also signalled by LED INTERFERENCE. Their impact on the
system depends on their shape and amplitude. Disturbances of this type may
generate false alarms, if their amplitude considerably exceeds the level of
activation and their shape is similar to the shape of the security. Sources of such
disturbances may include, for example:
● Closed metal frames,
● Rolled up roller blinds,
● Rolled up sections of cables,
● Securities located to close to the system.
2. Accidental impulse disturbances. These disturbances are mostly caused by
equipment which during operation breaks electric circuits causing emission of
electromagnetic disturbances. Such disturbances are also produced by metal
elements which move in relation to one another, which during friction break the
current inducted in them by electromagnetic field generated by the transmitter.
Their impact on the system is small and may appear only when the transmitter is
very sensitive. They can be observed as impulses that appear in an accidental
location; they are also signalled by LED NOISE. Such disturbances can be
● Equipment with brush engines,
● Fluorescent lights when being switched on,
● Metal elements that are rubbed against each other.
3. Repetitive impulse disturbances. These disturbances are caused mostly by other
EAS that operate at different modulation frequency or by devices that generate
disturbances with network frequency. The impact of these disturbances on system
depends largely on their strength and on the repetition frequency and their effect is
mostly a lowered sensitivity of the system. They can be observed as an increase of
the level of general disturbances; they are also signalled by LED NOISE. Such
disturbances can be caused by:
● EAS systems operating at different modulation frequency,
● Electric and electronic devices that operate close to the system.
4. Disturbances generated by other EAS which are not synchronised and are operated
at the same modulation frequency are a special type of disturbances. They cause
strong disturbances causing a decrease of sensitivity of the receiver and generation
of false alarms. They can be observed as slowly moving impulses with rapidly
changing amplitude. Remember that disturbances of this type may appear and
disappear in longer periods of time, which will depend on small difference
between modulating frequencies. Such disturbances must be prevented. They have
to be removed changing modulating frequency in the transmitter.
Table 6.1 presents typical sources of disturbances, the type of disturbances they cause and
their impact on the system.
Table 6.1. Sources of disturbances and their impact on the system
Disturbance type Impact on system
EAS systems 8.2 MHz with
the same modulating
▪ - ▪ ▪ ▪ ▪ ▪ ▪ ▪
EAS 8.2 MHz with other
- - ▪ ▪ ▪ ▫ ▪ ▫ ▫
- - ▪ ▪ ▪ ▫ ▫ ▫ ▫
Metal elements that create
resonance circumference on
frequency close to 8.2 MHz
▪ - - ▫ ▫ ▫ ▪ ▪ ▫
Metal elements moving in
relation to one another
▪ ▪ - ▪ ▫ ▫ ▪ ▫ ▫
Protected goods located too
close to the system
▪ - - ▫ ▫ ▫ ▪ ▫ ▫
Fluorescent lamp during
- ▪ - ▪ ▫ ▫ ▫ ▫ ▫
Brush engines - ▪ - ▪ ▫ ▫ ▫ ▫ ▫
Other electric or electronic
- ▪ ▪ ▫ ▫ ▫ ▫ ▫ ▫