For the speed of reaction of the security, fire-fighting system, emergency warning and control installations, a reed switch is used. The element reveals the state of the object, the appearance of smoke, dust, prevents unauthorized access.
What is a reed switch
The reed switch is an electromechanical device. It can open and close contacts when exposed to a magnetic field created by an electric or permanent magnet.
The interpretation of the term is a sealed contact, which is determined by its design. The device consists of a pair of ferromagnetic plates sealed in a glass capsule. The tank is filled with inert gas, nitrogen, dried air, has two exits. Such a flask prevents external factors and increases the reliability of the device.
To increase the switched voltage, the shell is evacuated.
Construction and appearance
The appearance of the reed switch is a sealed glass flask with magnetic core contacts. There is a gap between them. Elements are fixed by welding from the ends of the shell and are connected to the network by external parts. The sensor itself looks like a float and consists of three parts:
- glass flask;
- changeover contact;
- fixed contact.
Thanks to the rectangular contacts made of ferromagnetic wire, the device can close the network. The type of coating of contact elements depends on the power and dimensions of the product. Manufacturers use gold, rhodium, silver or permalloy wire.
Inert gas sensors or vacuum modifications do not corrode.
Reed switch classification
Reed switches are divided into types according to several criteria.
Normal contact status
Contacts are:
- closed - the circuit is opened by means of a magnetic field;
- switchable / bistable - one contact closes when the field is exposed, the other - if it is not;
- open - reed switch trips at the moment of magnetic field formation.
Switchable models have 3 pins.
Design
There are such sensors:
- sleeve - the glass shell is filled with inert gas or air;
- mercury - to improve switching, reduce resistance and eliminate vibrations, contacts are covered with mercury.
Sleeve reed switches have dry contacts.
Technical specifications
Depending on the technical characteristics there are:
- Reed switch - reed relay with high voltage insulation. It operates in a network under a voltage of 10-100 kV.
- A gas lawn is a modification that remembers the position of contacts after turning off the magnetic field.
- Herksikon - a relay with which an alarm and equipment with a power of up to 3 kW are activated. It features an increased switching current and arcing contacts.
Devices can replace an electromechanical relay.
Principle of operation
The principle of operation of the reed switch is based on the opening or closing of the network where it stands, under the influence of an electromagnetic field. Magnetic flux voltage determines the position of the contacts.The field is generated by a permanent or electric magnet.
The internal contacts of the device are magnetized at the moment of falling under the action of the power line. The attraction of elements is carried out under the action of overcoming the force of elasticity. This is the circuit closure. When the line is connected to a power source, current flows through the device.
This condition lasts until the termination of the influence of the power line. Contacts open without a magnetic field. To re-close, you will need to re-generate the field.
Reed switch is a small-sized switch, operating from the force of the magnetic flux.
Instrument Parameters
The type of equipment to which the magnetic reed switch belongs is relay. Before buying it, consider the following characteristics:
- Response time. It depends on the reaction time to the appearance of a magnetic field and does not exceed 2 μs.
- The strength of the magnetic field. Sensitivity depends on the ferromagnet and dimensions.
- Switching power. The limit of energy transmitted through the reed switch, taking into account the material and the cross section of the contacts.
- Ultimate stress. Determines the amplitude of the shutter speed signal.
- Resistance of closed contacts. With a smaller value, less signal power is lost.
- Permissible operating temperature. It depends on the manufacturer, but most often the element works at temperatures from -60 to +120 degrees.
- Frequency. Operation occurs at a frequency of up to 1 MHz.
- The number of switching cycles. Defines the number of operations.
- Capacity of contacts. Depends on the distance between the pads in the open position.
- Physical dimensions The horizontal balloon may be from 4 mm in length.
The capacity of the contacts is a spurious criterion.
Advantages and disadvantages
The positive factors for the use of reed switches include:
- lack of rattling on modifications with mercury outputs;
- reliability - the sensor will not break when dropped and exceeds the performance of a standard relay by 100 times;
- lack of risk of burning contact located in a vacuum or inert gas;
- small-sized sensor is designed for current, similar to a standard relay;
- the presence of galvanic isolation - devices are connected to the network in series;
- switching weak signals;
- a large number of inclusions without friction;
- operation without reference to a source of electricity.
The low cost of devices due to the lack of precious and refractory metals in the contacts.
The disadvantages of operating reed switches include:
- a lot of weight compared to relays with open contacts;
- the need to generate a magnetic field;
- do not always withstand shock and vibration;
- the need for protection from an external magnetic field;
- the difficulty of withdrawing contacts from a closed state;
- limited response speed.
When exposed to high current, spontaneous opening of the contacts occurs.
Reed sensor connection
The documentation regulating the connection process is supplied with the float sensor. Step by step they work like this:
- The node for creating a magnetic field is mounted on the moving part.
- The reed switch is fixed on the fixed part of the structure.
- Circuit closure. The movable part must adjoin tightly to expose the contacts to the magnetic field of the coil.
- Getting information about the health of the installation.
- Integrity Notification. The coil stops acting on the reed switch.
Sensors can be installed hidden or externally on steel or magnetically passive structures.
Practical use at home
Reed switches are used to protect keyboard synthesizers and industrial plants from explosions, and to increase equipment life.Parts control the mechanisms, and a float level sensor is needed to measure liquid in the tank.
Reed switches are placed in television equipment, displaying the opening or closing of the valves. Devices are compatible with computer or security systems - they inform whether the door or window is closed.
Electronic current meters have reed sensors.
Use in security systems
The peculiarity of the reed switch being introduced into the security complex is its adaptability to the base material. This technique eliminates the influence of the magnetic field of the structure on the magnetic field needed to trigger the device.
The sensor works on the principle of magnetic latch. The switch is installed on the door frame, frame, and then a cable is connected to it. An open mounting method provides the visibility of the device, but increases the magnetic field. For flush mounting, only sensitive modifications that respond to the magnet are suitable. Otherwise, there are risks of hacking.
Strengthening protection against unauthorized entry
As standard, the reed switch is located on the frame, and the magnet is on the door or window sash. The closed position of the structure provides the maximum proximity of the magnet to the sensor. At the time of opening, it is deleted, so attackers can easily find the installation location.
To increase the protection of the device are used:
- Hidden appliance. Closes the signaling circuit at the time of opening the sash. A minus of technology is the opening of the sash with the help of an additional magnet.
- Electric magnet. A feature of an electromagnetic lock with a reed switch is the complexity of counterfeiting due to random signal repeatability. Protection also works when the pulse is delayed.
An electromagnet needs a voltage of a certain duration.
The nuances of using reed switches
Before using or installing a reed switch, consider:
- The device is not compatible with ultrasound sources, as changes electrical parameters.
- The magnetic field affects the features of the switch.
- Upon impact, the inert gas breaks up, the cylinder may burst.
- The switch does not switch a large current due to the low power of the core.
Reed switches are not suitable for connecting powerful equipment.
The miniature reed switch is fast and designed for 4-5 billion operations. The device is compatible with the load of a low-voltage network and operates without reference to a source of electricity.
