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Magnetic contact detectors: the principle of construction and classification

The statistics of offenses related to the penetration of intruders into protected premises, says that the most "popular" and simple is the smashing of windows of windows, windows, as well as breaking of locks or doors. The probability of developing such a scenario, according to experts, is today 66.5%. Only a wall break can compete slightly with the beat of window openings and the breaking of doors (16.9%), other options (key selection, ceiling breakthrough, penetration through technological openings) hardly exceed 5%.

Who is he, the watchman of doors and windows

To protect doors, windows, gates, technological openings and other structures reliably from the threat of damage or hacking by intruders, adequate technical security measures were required. The magnetic contact detectors have become such means, among which the most notable position is occupied by the detector pointing magnetic point contact - reliable in operation and simple in mounting the sensor. Specialists give him high marks on the probability of detecting an attempt to penetrate the site of the object guarded by this device: it is 0.99, that is, in 99% of cases the offender will be detected by a sensor and the corresponding signal will go to the guard of the guard on duty.

With the help of such sensors, it is possible not only to provide an electrical signal to activate the audible alarm, but also to turn on the devices that block the doors (gates), the windows to open, and the objects to move.

Protected structures can be made of both magnetic (iron) and non-magnetic material (wood, aluminum, fiberglass, polyvinyl chloride). This does not affect the operation of the magnetic contact detector.

Principle of construction and device of the detector

It is in principle the construction of the sensor and its high reliability is laid. Here, the interaction of a sealed magnetically controlled contact (abbreviated as reed switch) serving as an actuating element and a magnet serving as a control element is used.

The executive element (reed switch) has a very simple design: it immediately combines the contact and magnetic systems, which are hermetically sealed in a glass cylinder. This design of the reed switch allowed to obtain characteristics exceeding the known contacts: speed, stable parameters, high wear resistance and reliability.

Contacts are made of soft magnetic material, they are separated by a gap of only 300-500 microns, which has certain disadvantages: increased sparking and increased contact resistance. This leads to a sudden "clumping" of contacts and a failure in the operation of the detector.

Since there are no intermediate links in the detector's reed switch, and the contacts commute a small electric current, the actuator has almost zero wear. This is also facilitated by the fact that the bottle contains nitrogen under high pressure, which eliminates the oxidation of contacts.

The control (master) element can be made in several variants: a permanent magnet or a magnetic circuit.

Classification of magnetic contact detectors

Detectors, like any other equipment, are subject to standardization, and this task is solved by the international standard IEC 62642-2-6. Its requirements apply to magnetic contact detectors designed to block doors, hatches, windows, containers.

This standard introduces four classes according to the degree of risk for these sensors: 1 - low risk, 2 - intermediate between 1 and 3 classes of risk, 3 - medium risk, 4 - high risk.

The above classification defines the critical and non-critical parameters of the detector for each class. For example, tripping and recovery distances, protection from damage to the alarm loop and total loss of the supply voltage must be mandatory parameters for all four classes.

In the Russian Federation, detectors of 1 or 2 classes of the international standard IEC 62642-2-6 are used, that is, they do not require an indication of damage to the protected structure, protection against foreign magnetic interference, low supply voltage.

In the Russian Federation, detectors of 1 or 2 classes of the international standard IEC 62642-2-6 are used, that is, they do not require an indication of damage to the protected structure, protection against foreign magnetic interference, low supply voltage.

Requirements for the functionality of magnetic contact detectors

Magnetic contact detectors must meet certain requirements for their functionality, namely:

  • The trigger distance excludes attempts to penetrate the attacker through a controlled construction or movement of the object of protection, as well as the replacement of parts of the detector without giving an alarm signal;
  • The recovery distance must prevent false alarms. - the relative displacement of the detector blocks (coaxiality) should not lead to the termination of its operation;

The indicators of the functionality of magnetic contact detectors depend on the type of sensor, its dimensions, installation location, material of the protected structure.

Marking of sensors

The magnetocontact sensor has a standardized name - the detector is a guard point magneto-contact IO. Then follows the numerical code characterizing the detection zones and the operating principle of the detector.

For example, the magnetic contact detector ИО 102 (SMK) has the marking ИО 102, which says that this equipment belongs to the type of detectors (the letter И), is used in security systems (letter О), has a point detection zone (figure 1) and a magnetic contact principle Actions (digits 0 and 2).

Detector Selection

The choice of equipment, such as a magnetic contact protection detector, is an important step. First of all, it must correspond to the place of installation, the material of the protected structure, the conditions of detention, as well as your requirements.

If it is necessary to protect a stand-alone object, this task will be performed by the detector magnetic alarm contact 102-2 (push-button).

To block doors, windows and other elements of the room is ideal for IO 102-20 / A2. He is also able to protect himself from sabotage ("trap"). That is, noise immunity of the sensor is an important aspect in the issues of its choice.
The conditions for keeping the detector should also be taken into account, and if the environment is explosive, then the IO 102-26 / B sensor will work for it.

The sensor is designed for air temperature from minus 40 to plus 50 degrees Celsius.

Also attention is drawn to the characteristics of the reed switch: they must match your conditions.

Mounting of detector blocks

The point magnetocontact point detector and the alarm loop are attached to the surface of the protected structure from the side of the room. The control element is fixed, as a rule, on the moving part of the structure (door, window, cover), and the executive unit with the alarm loop is fixed (door frame, frame, housing).

The way of fixing the detector depends on the surface on which it is mounted: on the tree - with screws, on the metal - with screws, on the glass - with the adhesive "Contact". A dielectric gasket must be installed between the detector blocks and the mounting surface.

The described method of installation refers to an open type, but in some cases there is a need for concealed installation of the sensor. For this, there are detectors of a cylindrical shape. The very form of the sensor allows you to set it secretly from prying eyes and do not disturb the interior of the room. But this type of installation has a certain drawback: it is of fundamental importance to observe the alignment of the ends of the actuator and control elements of the detector (within 2-3 mm).

Sabotage sensors and how to deal with it

According to amateurs, magnetic contact detectors are easily avoided, that is, ignored. And this is done, in their opinion, with the help of an external strong magnet.
In reality, this is far from the case, especially when it comes to steel structures. In this case, sabotage of the sensors is almost impossible, since the steel will close the action of the external magnet, and it will not reach the actuator.

In cases with non-metallic construction, it is not all that simple: a certain orientation of the external magnet is required, otherwise its effect on the actuating element can cause the reed switch to open and trigger the alarm.

If these arguments are unconvincing, then there are simple ways to protect against sabotage of detectors:

  • Application of two sets of magnetocontact sensors with multidirectional magnets spaced from each other by about 15 mm and connected in series;
  • The use of an additional shield in the form of a steel plate 0.5 mm thick or more;

Briefly about the shortcomings

The detector of the magnetocontact SMK has separate features of the actuating element that limit its use:

  • Dependence of contact pressure on the magnet force of the control element and control current;
  • The dependence of the switching capacity on the volume of the reed cylinder;
  • The length of the contacts contributes to their considerable bounce when vibrating and striking;

Conclusion

The magnetocontact detector IS deservedly is considered the most simple and reliable means of protecting objects and structures from intruders. A significant advantage of the sensor is its cheapness. Security systems containing this type of detectors are often given preference. Today, there are many security systems created by innovative technologies, but magnetic contact detectors remain in demand until now.

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