The cheapest and most numerous of security detectors. They stick on windows, doors, hatches and anything that can open and close - all sorts of lockers, for example, or hardware cabinets or safes - whoever has enough imagination for what. The simplest ones cost from 20 rubles, so installers are given them in bundles, like bunches of radishes. They are called QMS: magnetic contact alarms.
Official names IO-102-XX, where XX is the model number. For example, this one, at the beginning of the article - IO-102-14 (SMK-14). In general, people call them SMK or simply “esemkashki”.
Here is such a bunch:
The principle is the same for all - in one half (which is without wires) there is a magnet, in the other half there is a reed switch - a small relay, which, when it enters a magnetic field, closes (opens, switches - depends on the design of the detector). Standard burst security loops work, i.e. the majority of detectors close. By the way, “reed switch” is short for “sealed contact”. It's a tiny little glass flask with a contact group inside. Here is a disassembled SMK - a hollow body and a reed switch on the wiring:
In short, there is a reed switch on the jamb, a magnet on the door: you open the door, the contact opens, the loop opens - alarm. It's as simple as a slipper, and generally quite effective. It’s not a panacea, of course - you can break a window, saw through a door and get in without breaking the cable. In addition, I heard about a method of deceiving them - a powerful magnet is brought from the outside, it holds the reed switch in a closed state when it opens. Well, it’s not so simple, you need to know exactly where it is located, i.e. some preparation is needed, and the method of counteraction suggests itself. In any case, QMS are effective only when working together with other types of security detectors. The standard set is QMS, volumetric and acoustic glass break detectors - the next post about them will be in this section. There are a bunch of other types of security detectors at different physical principles, and we will get to them by praying.
Here is another from the same series - IO-102-2 (SMK-1). It will be a little more beautiful, but everything will be the same. By the way, both are for non-metallic surfaces.
For iron doors, gates and safes - the so-called garage QMS. They are significantly larger, the magnets are more powerful, the design is more brutal. Well, for example: SMK-20. What a handsome guy, everything looks like an adult, he’s only a little dirty - he was taken from somewhere, there are traces of a screwdriver bit in the grooves.
Well, or SMK-26. Recently some mystical tricks happened with one of them during the commissioning of the facility. One of the cables is broken when closed door, we go to monitor - everything is in order, we start to open the door - the cable returns to normal, then, naturally, with further opening it breaks as expected. It turned out that for some reason the reed switch opened when the magnet approached as close as possible. We turned the detector over and everything worked as it should. I didn’t find any hints of this effect in the passport; as usual, there was no time to figure it out, so it remained a mystery. There he is, the bastard:
And here are the detectors hidden installation, end They crash into the door and into the frame opposite each other. You drill a hole with a ten-point drill, squeeze out a little glue there and push it in there. This fits great. They are used in case of increased requirements for room design.
But a more complex and more expensive toy is the S2000-SMK from Bolid. The addressable device, a built-in microcontroller, connects to a two-wire communication line and exchanges signals with the S2000-KDL two-wire line controller. But according to the principle of operation of the sensor, it is the same QMS system. It has an interesting feature - to make it even more beautiful, the mounting holes are located inside the case, which is closed with an elegant lid (beauty is a terrible power). His brother for metal doors In general, it is called S2000-SMK “Estete”. So this lid constantly falls off - the latches are lousy. Before the object is handed over, we collect the lids in case they need to be rearranged somewhere, then afterward we go around them and put them on glue. Troublesome. Here he is, the dude, honored to star in my battle “magic suitcase”.
Not a single full-fledged security alarm or access control system can use a magnetic contact detector. It provides simple and reliable control of the position of windows, doors, barriers, crane beams and other moving parts of devices.
It began to be used almost immediately after its launch in mass production In the 40s of the last century, magnetically controlled contacts in a sealed housing were used, and it is still widely used. Its second name is “reed switch” (short for “sealed contact”) due to the main design element of the sensor.
Application area
Magnetic contact sensors are widely used in automation devices and security systems. They work in almost any climatic conditions and are not afraid of aggressive environments, dust, or gas pollution. Due to the functioning of the working contacts in an isolated inert environment, they are explosion-proof.
In automated complexes, magnetic contact sensors perform the functions of monitoring liquid level, linear movement, limit switches, etc.
Accordingly, they are used in almost all enterprises, regardless of the industry where automation devices are used. In security systems, they are often called door open/close sensors, although they are also used to monitor the position of windows, safes, desk drawers and other items. Due to the noiseless contact closure, they are used in stationary panic buttons and pedals, and are used in some glass break sensors.
Advantages and disadvantages
Among security sensors, a magnetic contact detector is the most reliable, cheap, simple and durable device.
The switched contacts are located in a sealed glass capsule in an inert gas environment, so they can be used in explosive and chemically active areas.
The contacts are coated with a layer of gold or rhodium, which ensures high wear resistance and reliability. They can operate within the range from -50 to +50 degrees Celsius. The control and switched circuits are galvanically isolated.
The disadvantage is contact bounce, but this can be overcome by turning on filters. The sensors react to strong external magnetic fields; the problem is solved by shielding them.
They are afraid of strong vibrations.”
Sensor design
Magnetic contact detectors are available with normally open, normally closed and switching contacts. Reed switches can be dry or wet. In the first case, they are in an inert gas; in the second, the contacts are moistened with mercury to prevent chatter. Nitrogen is usually used as a gas. For some reed switches, the bulb is evacuated to increase the switching voltage level.
The sensor consists of two parts, one contains a permanent magnet, sometimes an electromagnet, the other contains a reed switch with contact leads. Electromagnets are not found in security sensors. The contact system is a glass cylinder with an inert gas and two springs. Their ends overlap. If the reed switch is reversible, then there are three plates.
The distance between the contact pads is only 300-500 microns. Under the influence of a magnetic field, the contacts close. The bend of the spring is so small that it does not weaken and can be switched more than 10 billion times.
The inert environment protects the contacts from corrosion and sparks. Sensors come in overhead and mortise types. To protect against intruders, magnetically impenetrable screens are used. They are needed in order to exclude the influence of an external magnet on the reed switch. The materials of doors and windows are magnetically passive and magnetically active. Sensors are divided into two categories based on their ability to work on such objects.
The former have smaller dimensions and weaker magnets. They are placed on wood, aluminum and other products made of non-magnetic materials. Second – bigger size, With powerful magnet installed on metal doors. Wireless systems use only addressable magnetic contact detectors with a radio module.
The sensor's master element (a block with a magnet) is located in the moving part of the protected object (in the door), and the executive module is located in the stationary part (in the door jamb). For normal operation sensor, its parts should be located opposite each other.
Principle of operation
The principle of operation of a magnetic contact sensor is based on the use of the property of a magnet to attract iron and other metals from its group.
When the contacts approach the magnet at a certain distance, they close or open with each other under the influence of magnetic force. This depends on the design of the sensor. If the magnet is removed at some distance, the reverse process occurs.
Structurally, the contacts are located in a glass flask and are simultaneously a current conductor, a spring and a magnetic conductor. Since the energy of the magnetic field decreases exponentially with increasing distance, removing the magnet from the reed switch by 1-2 cm (opening the door slightly), it drops so much that it does not hold the spring-loaded contacts, and they open.
TOP 5 popular magnetic contact sensor models
- The security point magnetic contact detector IO 102-20 is used to monitor the condition of hangar gates, containers and other building structures for opening/closing and movement with notification to the control panel. The device can also be used as a limit switch. IO 102-20 A2P IB detectors marked OExiaIIBT6X are used in explosive areas and are connected via a special intrinsically safe line.
- The IO102-11M (SMK-3M) magnetic contact security detector is used to monitor windows and doors, create “trap” type devices with an alarm signal sent to the security panel. The contacts close when the gap between the sensor parts is no more than 6 mm and open when the gap is 25 mm or more. Switches voltage up to 100 V and current up to 0.5 A.
- The point magnetic contact detector IO-102-55 “Kenar” is used to detect the opening of a door or window made of wood, aluminum and similar materials, and has protection against sabotage. At a distance between the sensor parts of 12 mm it closes, at 45 mm it opens. Switching voltage 50 V, current 50 mA. Contacts are normally closed.
- To control the position of individual objects, metal doors, a magnetic reed switch model IO 102 2 push-button is often used. The reed switch and magnet are located in one housing, which simplifies installation.
- The EWD1 Eldes magnetic contact addressable wireless security detector works like regular opening/closing sensors. Only alarm and status signals are sent via radio. To set the address, you need to send an SMS message. In addition to everything there is alarm button on the device body. Operating frequency 866-869 MHz. It works offline for up to one and a half years. The radio signal transmission range indoors is up to 30 m, outdoors up to 150 m. Compatible with ELDES Wireless systems.
The choice of detector model depends on the customer’s wishes and safety requirements.
So that the sensors do not spoil appearance they can be hidden inside the door and jamb. For this purpose, cylindrical mortise detectors are available.
If the security system is large and complex, it is better to use overhead sensors with status indication.
In case of requirements for non-intervention in the interior or temporary installation, then the best option There will be the use of wireless detectors.
Depending on the characteristics of the protected object, a different number of sensors is installed.
If the locked door or hatch can be bent, then the detectors must be installed at intervals of 20 cm or together with vibration sensors.
When mounting on metal surfaces, it is necessary to provide a gap between the magnet and the surrounding metal to reduce magnetic field leakage.
Statistics of offenses related to the penetration of intruders into protected premises indicate that the most “popular” and simplest is breaking the glass of shop windows, windows, as well as breaking locks or doors. The probability of such a scenario developing, according to experts, is 66.5% today. Only breaking a wall can compete a little with beating window openings and breaking doors (16.9%), other options (picking keys, breaking the ceiling, entering through technological openings) barely exceed 5%.
Who is he, the guardian of doors and windows
In order to reliably protect doors, windows, gates, technological openings and other structures from the threat of damage or break-in by intruders, adequate technical security equipment. Magnetic contact detectors became such means, among which the most prominent position is occupied by the magnetic contact point security detector - a sensor that is reliable in operation and easy to install. Experts give it a high rating in terms of the probability of detecting an attempt to enter the territory of an object protected by this device: it is 0.99, that is, in 99% of cases the criminal will be detected by the sensor and the corresponding signal will go to the remote control of the security guard on duty.
With the help of such sensors it is possible not only to supply an electrical signal to turn on sound alarm, but also the inclusion of devices that block doors (gates), windows for opening, and objects for movement.
Protected structures can be made of both magnetic (iron) and non-magnetic materials (wood, aluminum, fiberglass, polyvinyl chloride). This does not affect the operation of the magnetic contact detector.
Construction principle and device of the detector
It is in the principle of constructing the sensor that its high reliability is based. It uses the interaction of a sealed magnetically controlled contact (abbreviated as a reed switch), which serves as an actuator, and a magnet, which serves as a control element.
The actuator (reed switch) has a very simple design: it immediately combines contact and magnetic systems, which are hermetically sealed in a glass container. This design of the reed switch made it possible to obtain characteristics superior to known contacts: speed, stable parameters, high wear resistance and reliability.
The 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 sudden “sticking” of contacts and failure of the detector.
Since there are no intermediate links in the detector reed switch, and the contacts switch small electricity, then the actuator has almost zero wear. This is also facilitated by the fact that the cylinder contains nitrogen under high pressure, which eliminates contact oxidation.
The control (setting) element can be made in several versions: or 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, and containers.
This standard introduces four risk classes for these sensors: 1 - low risk, 2 - risk intermediate between classes 1 and 3, 3 - medium risk, 4 - high risk.
The above classification determines the critical and non-critical parameters of the detector for each class. For example, response and recovery distances, protection against damage to the alarm loop and complete loss of supply voltage should be mandatory parameters for all four classes.
IN Russian Federation Detectors of class 1 or 2 of the international standard IEC 62642-2-6 are used, that is, they do not require indication of detection of damage to the protected structure, protection from foreign magnetic influences, or low supply voltage.
Requirements for the functionality of magnetic contact detectors
Magnetic contact detectors must meet certain requirements for their functionality, namely:
- the triggering distance excludes an attempt by an intruder to penetrate a controlled structure or move a protected item, as well as replace parts of the detector without sending an alarm signal;
- the recovery distance must exclude false alarms of the detector. - relative displacement of the detector blocks (alignment) should not lead to the termination of its operation;
The functionality of magnetic contact detectors depends on the type of sensor, its size, installation location, and the material of the protected structure.
Sensor markings
The magnetic contact sensor has a standardized name - security point magnetic contact detector IO. This is followed by a digital code characterizing the detection zones and the operating principle of the detector.
For example, a magnetic contact detector IO 102 (SMK) is marked IO 102, indicating that this equipment belongs to the type of detector (letter I), is used in security systems (letter O), has a point detection zone (number 1) and has a magnetic contact principle actions (numbers 0 and 2).
Detector selection
The choice of equipment such as an IO magnetic contact security detector is an important step. First of all, it must correspond to the installation location, the material of the protected structure, the conditions of detention, as well as your requirements.
If it is necessary to protect a separate object, then this task will be performed by the security magnetic contact detector IO 102-2 (push-button).
IO 102-20/A2 is perfect for blocking doors, windows and other room elements. He is also able to protect himself from sabotage ("trap"). That is, the noise immunity of the sensor is an important aspect in matters of its selection.
The conditions under which the detector is kept must also be taken into account, and if the environment is explosive, then the IO 102-26/V sensor is suitable for it.
The sensor is designed for air temperatures from minus 40 to plus 50 degrees Celsius.
Attention is also drawn to the characteristics of the reed switch: they must meet your conditions.
Installation of detector blocks
The magnetic contact 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 mounted, as a rule, on a moving part of the structure (door, window, cover), and the control unit with an alarm loop is mounted on a stationary part ( doorjamb, frame, body).
The method of attaching the detector depends on the surface on which it is mounted: on wood - with screws, on metal - with screws, on glass - with “Contact” glue. A dielectric gasket must be installed between the detector blocks and the mounting surface.
The installation method described applies to open type, but in some cases there is a need for hidden installation sensor For this purpose, there are cylindrical detectors. The very shape of the sensor allows it to be installed hidden from prying eyes and not disturb the interior of the room. But this type of installation has a certain drawback: it is fundamentally important to maintain the alignment of the ends of the actuating and control elements of the detector (within 2-3 mm).
Sabotage of sensors and how to deal with it
According to amateurs, magnetic contact detectors are easily bypassed, 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 if we're talking about o In this case, sabotage of the sensors is practically impossible, since the steel will close the action of the external magnet and it will not reach the actuator.
In cases with a non-metallic structure, everything is also not simple: a certain orientation of the external magnet is required, otherwise its effect on the actuator can cause the reed switch to open and trigger the alarm.
If these arguments are unconvincing, then there are simple ways protection against sabotage of detectors:
- the use of two sets of magnetic contact sensors with multidirectional magnets located about 15 mm from each other and connected in series;
- the use of an additional screen in the form of a steel plate with a thickness of 0.5 mm or more;
Briefly about the disadvantages
The magnetic contact detector SMK has certain features of the actuator that limit its use:
- dependence of contact pressing on the magnet strength of the control element and control current;
- dependence of the switching capacity on the volume of the reed switch cylinder;
the length of the contacts contributes to their significant rattling during vibration and shock;
Conclusion
The IO magnetic contact detector is deservedly considered the simplest and most reliable means of protecting objects and structures from intruders. A significant advantage of the sensor is its low cost. Security systems containing this type of detector are often preferred. Today there are many security systems created according to innovative technologies, but magnetic contact detectors remain in demand to this day.
Magnetic contact sensors (detectors) are installed, as a rule, one for each blocked element, hidden or open method. If there is justification in the project (or inspection report) for blocking door openings, two sensors can be installed for each blocked element, and installation options with protection against sabotage can be used.
The number of magnetic contact sensors (detectors), the method of their installation, and the need for protection against sabotage are established in the design specifications.
Sensors are installed, as a rule, in the upper part of the blocked element from the side of the protected premises at a distance of up to 200 mm from the vertical or horizontal line of the blocked element. Depending on the release distance of the magnetic contact sensor (detector) and the design of the blocked element (thickness and material of the door leaf, window), in cases justified in the project (or inspection report) it is permissible to install the sensor (detector) at a greater distance (closer to the axis), provided the sensor (detector) issues an alarm notification when you try to open a door (window) before a gap forms between door leaf(window) and door frame(window frame).
If it is impossible to install magnetic contact sensors (detectors) in the upper part of the blocked element (due to structural or architectural features windows and doors) it is allowed to install them on the side parts (opposite the hinges) of frames and doors. It is allowed to install such sensors (detectors) on the lower parts of window frames. In this case, it is preferable to install the reed switch (magnetically controlled contact) of the sensor (detector) on a stationary part of the structure (plinth, door frame), and the permanent magnet assembly on a moving part (door, window frame). In order to meet the requirements of technical aesthetics when blocking similar types building structures magnetic contact sensors (detectors) must be installed at equal distances from the solution line of the blocked element. The distance and permissible misalignment between them must comply with the technical documentation of the manufacturers.
When installing magnetic contact sensors (detectors) on metal surfaces, if necessary, to increase the reliability of the sensor (detector) between the magnetocontaining unit of the detector and metal surface Gaskets made of non-magnetic material (wood, textolite, ebonite or getinax) with a thickness of up to 25-30 mm are installed.
During installation, it is not allowed to subject the sensor units (detectors) to impacts, and also to bend the leads of the magnetically controlled contact unit.
When using magnetic contact sensors (detectors) as traps on internal (transition) doors, they must be installed on one side (internal or external) of the door, and, if necessary, on both sides. In these cases, it is allowed to install sensors at a distance exceeding 200 mm from the vertical line of the door opening.
When installed in an open manner, the reed switch and magnet are attached directly to the surface of the element being locked.
Their fastening to the surface is done:
- with screws - on wood;
- screws - on metal;
- glue - on glass (glass doors).
The contact pins are connected to the alarm loop using mounting junction boxes or to the loop wire by twisting, followed by soldering the connection points with solder.
The soldering points and leads of the magnetically controlled contact to the junction box are insulated with polyvinyl chloride tubes.
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Today it is no longer enough to simply install a good and reliable metal armored door. Modern thieves find approaches and use intelligent solutions to open any lock systems.
In order to feel completely safe, door structure equipped with additional protective systems - these can be simple alarms with a minimum set of functions or powerful and serious security systems. Both the simple system and the complex one have one common part - this is the door opening sensor. These devices are time-tested and can serve their owner for a very long time. This affordable way protecting your apartment or house from burglary and uninvited guests.
Today, the security systems market offers many similar devices. These are traditional wired solutions or wireless. GSM devices are also popular today. Let's talk about how to choose a suitable sensor, how they work, and find out their installation features.
Reed switch for safety
The reed switch sensor is perhaps the most popular among all those that can be installed on front door. These solutions are widespread in almost many industries, but they are also used in security systems. The advantage of a reed switch is that it is an affordable, easy-to-install and very effective sensor that responds to the opening of doors, gates, hatches, windows - any moving structures.
Previously, electromagnetic relays were used for these purposes, but these devices could not cope with the assigned tasks - their switching speed was too low. In addition, rubbing parts accelerated wear of the contacts, which led to relay failures. But after the creation of reed switches, the relays were forgotten.
Application
A magnetic contact-type door opening sensor or a reed switch can respond to the closing or opening of moving parts that provide access to the room. These broadcasters are located inside buildings, they are invisible to the eye, their operation is almost trouble-free - using miniature sensors, they are ensured reliable protection remote objects.
With the help of such sensors, it becomes possible to serious investments means to organize an effective security system in an apartment or cottage. You can install such a door opening sensor anywhere - on safes, store windows, inside apartments on steel doors.
Principle of operation
The reed switch is a sealed switch. Its contacts are made of a special ferromagnetic alloy.
The principle of operation is based on the use of interaction forces that act on two ferromagnetic bodies in a magnetic field. These forces force spring contacts deform and move before they connect - this is how the door close sensor works. When a magnetic field of a certain strength is created, the ends of the springs are attracted and closed. When the strength of the magnetic field decreases (the two parts of the sensor are separated), the springs are released and the contact is broken, resulting in an alarm.
A constant electrical signal is passed through the security alarm circuit - it passes through the door opening sensor. A constant magnetic field can also be used. According to the standard, the reed switch response threshold can be adjusted from 30 to 50 mm. If you open the door at a distance of 30 mm, the alarm panel will receive a signal that the contacts of the magnetic sensor are broken.
Structurally, these detectors are designed in minimum sizes. The sensor consists of two magnetic relay blocks in a plastic case. The door opening sensor is covered with a double layer of insulation - this helps eliminate false alarms.
Popular sensors for security systems
Among those involved in the installation of security equipment, a reed switch is understood as a sealed contact. SMK is the name given to magnetic contact alarms.
The most commonly used IO 102-20 is standard solution, where the distance between the contacts in the closed state is 24 mm, and in the open state 70. This magnetic opening sensor is equipped with a cable 350 mm long and 3.5 mm thick. One part of it is installed on the door.
There are other types of similar sensors - the differences among them are purely design. Yes, they may differ. different types housing protection, response threshold.
Advantages and disadvantages of reed sensors
One way or another, reed relays form the basis of any modern door security systems. They have some disadvantages and advantages.
So, the compact design is considered an advantage, which allows you to install this element anywhere. Also among the advantages is high tightness - this is especially important if the room high humidity. In addition, it is noted high speed relay operation, its durability.
There are also disadvantages. The most significant is strength. With mechanical impact, the device will simply fail. In addition, the door closing sensor reacts to magnetic fields that are located next to it. When a high current is applied to the reed switch, the circuit may inadvertently open.
Wireless solutions
Many people today are trying to use wireless technologies. This trend has also been noticed in security systems. Convenience wireless alarms lies in the absence of wires. All elements of the system are connected via a special protocol to the system console.
The wireless door opening sensor is the same reed switch. The design consists of a communication module, which houses a reed relay with open contacts. The second part is a magnet that closes the relay contacts.
It is recommended to mount the radio transmitting module on the door frame, and the magnet directly on the door so that when the door is closed it is opposite the radio transmitting part and can close the contacts of the magnetic relay. The operating principle of this door closing sensor is based on a reed relay. When the doors open, the circuit is broken, the contacts open - an alarm signal is sent to the main module or the central GSM unit. An alarm can also be indicated by a light indicator. It will also inform you that it is time to replace the device’s batteries.
The gap at which this device will operate starts from 10 mm and can be up to 20 mm. The device operates at a frequency of 433 MHz, and its range is up to 150 m in line-of-sight mode in open space. This wireless door sensor is powered by a 12 V battery. This battery will last the device for two years of continuous operation.
This is a typical door open sensor. All devices have approximately the same specifications. They should be selected based on the specific situation.
GSM door alarm
There are also such devices on the market. They are seriously different from full-fledged wireless security alarms. This device extremely simple, but at the same time can reliably protect property.
The devices are GSM sensor door opening is a special controller equipped with a GSM module. If the sensor is triggered, the controller will send an SMS to the home owner. This simple device can be installed almost anywhere there are two doors. The operation is based on the same reed relay.
To control this security device, manufacturers offer several SMS commands that allow you to turn the system off or on, set the object to security, and enter a number for sending SMS. Some models may have a mode for listening to what is happening, for example, in an apartment - this mode can also be launched using SMS commands.
In order to secure the alarm, the manufacturer has provided a special Velcro. This simplifies repeated installation/disassembly of the device. During installation, you need to carefully set the distance from the controller to the magnetic sensor - the alarm threshold is 10 mm.
As you can see, with the help of such door opening sensors you can reliably protect the front door and apartment, private cottage or any other object.
