Advantages of using a reed switch sensor on a door

The door closing sensor is a modern device based on the principle of a sealed contact, which is abbreviated as a reed switch. The reed switch can be installed on doors, windows, and used in various types of industry, security systems, relays, and telephony systems. Reed sensors have a lot of advantages and wide functionality, which is why they are in great demand on the product market. Today we will talk about the design of door opening sensors. Read more about installing reed switches on the door in the following article.

Reed switch: what is it

The reed switch consists of two ferromagnetic contacts, which are sealed in a sealed glass flask

To detect the opening of doors, safes, windows, gates, hatches, etc., magnetic contact sensors are used. This device is based on a sealed contact - a reed switch. This is where another name for sensors comes from – reed opening sensors.

The reed switch consists of two ferromagnetic contacts, which are sealed in a sealed glass flask. When a magnetic field occurs, the contacts change their state (close or open). The contacts are in an inert gas or vacuum, so if a spark occurs they burn slightly. This determines the durability of reed switch sensors - the service life of the devices is considered infinite (excluding cases of breakage and the passage of high currents). Compared to classic relays, reed switches have high operating speed and are smaller in size.

In addition, reed sensors belong to the class of inexpensive products, since there is no need to use refractory precious metals for contacts. The disadvantages of the devices under consideration include: fragility (it is not recommended to use reed switches under conditions of shock loads and strong vibrations); the appearance of rattling noise when turned on, which provokes operation in a short period of time; sticking of contacts, leading to the need to replace the reed switch; If the power supply is connected incorrectly, the operating time of the reed switch may be reduced.

Based on the type of contacts, there are three types of sensors: normally closed, normally open, and switching. This leads to the following main characteristics of opening sensors:

• contact closure distance;
• the distance between the reed switch and the magnet at which the detector contacts close;
• contact opening distance;
• the distance between the reed switch and the magnet at which the detector contacts open;
• contact holding distance;
• the distance between the reed switch and the magnet at which the detector contacts remain in their original position.

Installation procedure

Correct installation largely determines how effectively the Xiaomi door sensor will work. The work is performed in the following sequence:

• Preparing the base. The surface is thoroughly cleaned of all available contaminants. If there are differences in height, the base should be leveled. After leveling, the surface is thoroughly cleaned and dried. This will ensure reliable fixation of the elements on the surface of the doorway;
• Selecting a location for the sensor elements. Their spatial position is selected in such a way as to meet the manufacturer’s requirements for the distance between elements;
• The protective film is removed from the back of the main unit and the magnet;

• The sensor is applied and securely fixed to the base. It is preferable to use a door jamb to place it. This will protect the device board from adverse effects during operation;
• A magnet is glued to the prepared area. When placing it, alignment of the corresponding marks on the main block and the magnet is ensured. This will allow you to achieve the correct relative position of the elements. The magnet is attached to the sash.

During the installation process, not only the alignment of the marks is ensured, but also the gap regulated by the manufacturer is controlled. Its size should not exceed 22 mm. Otherwise, when opening/closing the leaf, the device will not send a control signal to the devices paired with it.

Door and accessory opening sensor

To control the time and place of opening doors and units (trailer doors, etc.), “reed switch” sensors on a magnet can be used. The sensor consists of two halves, usually a movable one - a magnet attached to the door and a non-movable one - the reed sensor itself.

The reed opening sensor is connected to the GPS/GSM terminal; if the sensor status is measured (door opening), the tracker sends a message, depending on the settings, in two ways: 1) as an SMS message to a pre-recorded mobile phone; 2) to the server via the mobile Internet. In the second case, the dispatcher sees an alarm message on the computer and the location where the sensor is triggered (door opening).

Among reed sensors there are models with wireless information transmission. The reed switch sensor does not have to be connected directly to the GPS/GSM terminal by wires.

There are also alternative sensors for monitoring the integrity and opening of various mechanisms. Among them:

The limit switches are made in the form of a mechanical button with a spring. When this button is pressed, a message is sent. It is used as a sensor for opening the front panel of a car, opening the hood, opening the doors;

Tank opening sensor (RFID technology). The sensor consists of a tank cap with a built-in radio tag (RFID) and a reader that is attached to the tank neck. If the lid is removed, the sensor signals the opening of the tank. It is almost impossible to deceive such a sensor.

Setting procedure

To configure the Xiaomi door and window opening sensor, you need to install the Mi Home application on your smartphone. Instead of a smartphone, any other device connected to the Internet can be used. Their main purpose is to provide a connection between the device and the user via wireless communication.

After the application is installed, connect the sensor in the following sequence:

• Check the functionality of the device. Before use, remove the insulating layer of the battery;
• The application starts. In the menu that appears, select the name “Home”. You can go to the page with devices by clicking on the “+” symbol. This takes you to the page used to add devices (“Add Device (Accessory)”). To add a sensor, click on “Door and Window Sensor”. After this, the corresponding icon will begin to blink in the application, indicating that the device has been identified;
• The settings are restarted. For this purpose, a special key-clip is used, inserted into the hole provided for this purpose on the device body.

If the connection does not occur, the procedure is repeated, moving the device closer to the hub. In this case, the level of communication will be much higher. Approaching the hub, the procedure is repeated. To reconnect the product, press the button on the case once. Long press for 3 seconds will reset the settings completely.

If the choice was made correctly, the device will appear in the list of devices that are part of the Smart-home intelligent system. After the device is installed, it begins to be configured. The order of actions depends directly on the goals being pursued. A suitable scenario is selected for this purpose.

The most popular among users using Xiaomi Aqara Window Door are synchronization with:

• devices of the intelligent system. Most often, the sensor is configured to ensure full interaction with the humidifier or air purifier. The work of the latter is relevant only if the windows and doors are completely closed. If a flap opens for some reason, the sensor will send a corresponding signal to the purifier or humidifier control unit. The latter will turn off and turn on only when the sash is closed again. When a window is opened for ventilation, the sensor can be switched to standby mode;

• lighting control system in the hallway. In this case, when the door is opened, the sensor will send a control signal to the smart socket, and the lighting in the room will turn on. For the script to work, it must be configured correctly;
• security system. This is true for those who spend a long time outside the home. As soon as a window or door in the apartment opens, for example, due to unauthorized entry, a corresponding notification will be sent to the user’s phone. The device also allows you to activate the alarm function. To ensure the maximum level of security, Sensors should be installed on every window. This is especially true for owners of private houses and apartments located on the ground floor. In this case, the likelihood of entry into the house in the absence of the owners will be minimized. Especially if the operation of all devices that are part of the intelligent smart home system is optimized. Thus, the “Vigilance” mode allows you not only to send a corresponding notification to your smartphone, but also to start a recording mode of what is happening around you.

You should not think that the selected scenarios will remain unchanged for a long time. If you wish, you can always make a transition from one to another while away from home, and also edit it remotely.

Reed sensors

Reed sensors Reed sensors are common as sensors for opening doors and windows, for protection against unauthorized entry into objects, in security systems.

These magnetic contact sensors are installed on doors, gates, windows and any other massive structures and objects that need to be protected from unwanted opening, movement, or destruction.

The reed switch (sealed contact) is the main element of such a sensor, and makes it a reliable, safe, and durable, at low cost, component of security systems.

The reed switch is a hermetically sealed glass cylinder, in which two permalloy contacts are usually placed, and the medium inside the cylinder is high-pressure nitrogen, which eliminates oxidation processes inside this important electronic component. Its contacts are coated with a special metal, such as molybdenum, titanium, tungsten or gold, this gives them durability and wear resistance (the working life of the reed switch is more than a million operations).

The principle of operation of the reed sensor is quite simple. It consists of two parts: master and executive. A permanent magnet is used as a driving part, and a reed element is used as an actuating part. As a rule, these parts are very similar in appearance, they have the same body. The part containing the magnet is usually placed on a movable structure, for example on a door, and the sensor itself, for example, on a door jamb.

When the door is closed, the elements are next to each other, and the magnet, acting on the reed switch contacts, keeps them in a closed state, in this position the typical security mode is observed. If the door is opened in this mode, the magnet will no longer hold the reed switch contacts closed, and an alarm will occur. The technical documentation for the sensor indicates what the distance between the two components of the sensor must be for it to work reliably.

The reed switch (sealed contact) is the main element of such a sensor, and makes it a reliable, safe, and durable, at low cost, component of security systems

There are different types of sensors for different conditions:

• For surface mounting on magnetically passive structures.
• For surface mounting on steel structures.
• For hidden installation on magnetically passive structures.
• For concealed installation on steel structures.

The differences here are quite justified, since a massive steel door, for example, requires the installation of a more powerful magnet, since part of the magnetic field is absorbed by the steel, and in addition, the installation gaps during installation must be increased, this is due to the installation features of such a door itself.

At the same time, installation on a wooden or PVC door or window does not require any special conventions, and the sensor for them is quite simple; it can be screwed or simply glued.

Hidden installation, in turn, allows the equipment to fit into the interior; the elements of such a sensor are inserted into the holes and securely held there with fastening latches for fixation. As you can see, flush-mount sensors look different than surface-mount sensors.

To protect against illegal entry by attempting to deceive the sensor with an external magnet, when installing the sensor, you should use simple protective measures, the main ones of which are two.

The first is to place two sensors so that the magnetic fields of their magnets are directed in opposite directions, and the sensors themselves are located at a short distance from each other. Then the attacker, trying to deceive the sensor, will use his magnet to open one of the reed switches, and thereby turn on the alarm.

The second method is to place a steel plate with a thickness of 0.5 mm between the part of the sensor containing the reed switch and the intended place of influence by an external magnet, then the plate will serve as a magnetic shield. The plate size should be 60 by 20 mm for open sensors, and 20 by 30 mm for hidden ones. The plate must be located at a distance of at least 15 mm from the reed switch.

Kit contents

The sensor can be part of an intelligent smart home system or purchased separately to expand its capabilities. In the latter case, the product is supplied in a small cardboard box, packed in a tight bag to properly protect the contents during transportation.

The product size is relatively small. It measures 40.8×20.8×11 mm. This allows you to immediately determine the possibility of using this product to equip a specific window or doorway. Considering that the width is only 2 cm, it can be installed even in a window opening with a thin sash.

In addition to the product itself, the package includes:

• double-sided tape, with which the product will need to be fixed to the wall surface. Its quantity is sufficient so that, if necessary, the user can move the sensor to another place. At the same time, the adhesive tape allows you to form a high-quality connection without damaging the base material;
• round batteries CR2032, from which the device can operate for a long period of time. The duration of use of the product largely depends on the intensity of use. On average, one nutrient is enough for the user to use the sensor for 2–5 years.

Any tools that may be required during the assembly or installation of the product are not included in the package. The user can assemble and install it without using any fixtures or tools.

The company claims that the product can be used over a fairly wide temperature range. It remains operational at temperatures from −10 °C to +50 °C. When operating outside the specified range, you may encounter not entirely correct operation of the device. It will either stop working completely or start issuing incorrect commands. At the same time, it is the best option for a private home.

Operating principles of reed switches

The word “reed switch” comes from the phrase “sealed contact”. This device is a sealed switch with special spring contacts made of ferromagnetic material, which are in contact against the influence of a magnetic field and current. According to the principle of operation and mode of operation, reed switches are divided into the following types:

• closing;
• opening;
• with switching type contacts.

Externally, the reed switch is a glass cylinder (flask). If you bring a magnet near, two plates made of permalloy wire are attracted, and the contact instantly closes. If you remove the magnet, the reed switch contacts open (opening occurs). The distance between the contact parts ranges from hundredths to tenths of a millimeter.

According to their design, magnetically controlled reed switches are divided into:

• “dry” with regular contacts;
• “wet”, in which the contact surface is moistened with a drop of mercury, which prevents chatter.

Magnetic gas reed switches are characterized by a breakdown voltage of up to 500 V, sometimes up to 800 V. In vacuum devices, the voltage reaches up to 5000 V. The response time is 0.5/2 milliseconds, and the release time is from 0.1 to 0.7 milliseconds.

Note. Normal is an open contact, which is open in the absence of a control action, in this case a magnetic field. Accordingly, it is normal - a closed contact is closed in the absence of a magnetic field.

Of course, a magnetic field is always present, for example the Earth's magnetic field. And it seems impossible to say that there is no magnetic field at all. But the Earth’s magnetic field is not enough to trigger the reed switch, so it can be neglected and we can say that there is no magnetic field, in this case external.

Types of reed switches

Just like regular contacts, reed switches can be making (1 normally open contact), switching (1 changeover contact) or opening (1 normally closed contact). This is a division based on functional characteristics.

Based on their structural and technological characteristics, reed switches are divided into two large groups: with dry contacts and with mercury contacts. The first type is called dry reed switches, and the second is called mercury reed switches. Actually, there is nothing special in the operation of dry reed switches, compared to conventional contacts.

In mercury reed switches, inside a sealed glass case, in addition to the contacts, there is also a drop of mercury. The purpose of this mercury droplet is to wet the contacts during operation to improve the quality of the contact by reducing the contact resistance, and also to get rid of contact bounce.

Bouncing is the vibration of contacts when closing and opening, which, with a single operation, leads to repeated switching of the transmitted signal, and in addition to a significant increase in the response time. Imagine that such a bounce would be present in an audio amplifier when switching the input signal! In the case when such a rattling contact works in conjunction with digital microcircuits, it is necessary to take measures to suppress the chatter in the form of RC chains or RS triggers.

Various contacts, including reed contacts, are also used in modern microcontroller circuits, but in them contact bounce is suppressed by software. This also reduces the performance of the system as a whole.

Advantages of a reed switch and its application

The following advantages of the reed switch are distinguished:

• installation in conditions of high humidity, dust and extreme temperatures (60/150 degrees Celsius);
• high performance (0.5-1.5 milliseconds);
• huge service life (up to ten million switchings);
• isolation of control circuits and loads is entirely galvanic;
• withstand high mechanical loads.

Reed switches are used in:

• industrial sensors;
• relays of all types;
• automotive specialized sensors;
• security alarm sensors and detectors;
• telephony and communication systems.

The SAFETY Hypermarket online store offers a large selection of magnetic contact elements. Buy a sensor for opening doors, gates, windows and other structures. The quality of goods, favorable price offers and fast delivery set our company apart from others. For you - installation of a reed switch unit of the required type, which will last for a long time.

Device Features

Using this Xiaomi Mi Smart device has many advantages. The choice in its favor is made due to:

• presentable appearance. The device fits harmoniously into the interior of any room. Considering that most windows are white, the sensor becomes almost invisible;
• the ability to ensure a sufficient level of security for your home or office. While away from home, you can know exactly the situation with windows or doors. In the event of an emergency situation and the settings are correctly performed, it will be possible not only to obtain information, but also to see how the situation is developing;

• the possibility of using a ZigBee wireless connection that expands the functionality of the device. It can be connected to other elements of the intelligent “smart home” system;
• lighting settings in the hallway. This is convenient when guests come to the house. When you press the bell or open the door in the hallway, the light will turn on;
• the presence of a regime away from home. The system will automatically notify the user as soon as a stranger is inside the house, or someone simply rings the doorbell. If the intelligent system includes video cameras, the user will see the current video;
• ease of installation. The sensor can be placed in any window or doorway. The ease of fixation on the surface greatly simplifies the installation process; just clean the base, remove the protective film and attach the device to the base;
• Possibility of operation in a wide temperature range and at different humidity levels. The value of the latter can vary in the range of 0–95%.

High-quality plastic is used to manufacture the device. Thanks to this, the product is of high quality and durable. It does not deteriorate after repeated long-term use. A well-thought-out interface and ease of operation allow even an inexperienced user to understand the principle of operation and installation procedure of the device.

Basic rules for installing opening sensors

Wired door opening sensors are installed on the part of the structure to be opened, either directly on the vertical solution line, or at a distance of no more than 200 from it. Since a reed switch is included in the electrical circuit of the signaling loop, it is installed on the stationary part, and the magnet on the moving part.

Installation of a wireless door sensor is simpler because it does not require wiring. However, it is also recommended to install the reed switch on a stationary part of the structure to avoid impact impacts.