Activation reed switch is the operation or process of causing the reed contacts inside the reed switch to change from an open state to a closed state, thereby completing the circuit. A reed switch, also known as a magnetic reed switch, is an electrical switch controlled by an external magnetic field.
What is the working design of activating a reed switch?
Structural Foundation
Basic Structure: A reed switch typically consists of two ferromagnetic reed blades sealed in a glass tube. The reeds are made of materials like iron and nickel and are in an overlapping state with a small gap in between, usually just a few microns. The contacts of the two reeds are plated with hard metals such as rhodium and ruthenium to improve the service life. The glass tube is filled with high-purity inert gas like nitrogen, and some reed switches are vacuum-sealed to enhance high-voltage performance.
Magnetization Process
External Magnetic Field Introduction: There are two main ways to introduce an external magnetic field. One is by using a permanent magnet. When a permanent magnet approaches the reed switch, the magnetic field of the magnet acts on the reed blades. The other is by using an electromagnetic coil. When the reed switch is placed at the central axis of the coil and current passes through the coil, a magnetic field is generated, and the magnetic field is the strongest at the central axis position.
Magnetization of Reed Blades: Under the action of the external magnetic field, the reed blades are magnetized and become part of the magnetic circuit. The two ends of the reed blades acquire opposite magnetic polarities.
Contact and Conduction
Force Analysis
The magnetic force generated by the magnetization of the reed blades causes an attractive force between them. When the magnetic force is strong enough to overcome the elastic force of the reed blades themselves, the two reed blades attract each other and come into contact.
Circuit Conduction: The contact of the reed blades leads to a change in the circuit state, enabling the circuit to conduct electricity, thus achieving the activation of the reed switch.
Recovery Process
Magnetic Field Removal: When the external magnetic field is removed, such as when the permanent magnet is moved away or the current in the electromagnetic coil is cut off, the magnetic field around the reed blades disappears.
Reset of Reed Blades: Due to the elastic force of the reed blades themselves, they return to their original non-contact state, disconnecting the circuit and completing a working cycle of the reed switch.
What is the principle of activation reed switch？
Magnetic Field Generation
Permanent Magnet: A permanent magnet can be used to approach the reed switch to create a magnetic field. For instance, in a door magnetic sensor, a permanent magnet is installed on the door frame, and the reed switch is installed on the door. When the door is closed, the magnet and the reed switch are close to each other, and the magnetic field of the permanent magnet acts on the reed switch.
Electromagnetic Coil: When an electric current passes through the electromagnetic coil, a magnetic field is generated. The reed switch is placed within the magnetic field range of the coil. The magnetic field generated by the coil is utilized in some electronic devices that require remote control or precise control of the magnetic field, such as in some automatic control systems.
Magnetic Domain Alignment: The reed blades in the reed switch are made of ferromagnetic materials like iron-nickel alloys23. When no external magnetic field is present, the magnetic domains inside the reed blades are randomly arranged, and the overall magnetic effect is not obvious. When an external magnetic field is applied, the magnetic domains inside the reed blades start to align in the direction of the external magnetic field, causing the reed blades to be magnetized.
Pole Generation: As a result of magnetization, opposite magnetic poles are induced at both ends of the reed blades. For example, if one end of a reed blade is magnetized to be the N pole, the other end will be the S pole.
Contact and Conduction of Reed Blades
Magnetic Force Overcoming Elastic Force: Due to the magnetization of the reed blades, an attractive force is generated between the two reed blades. When the magnetic force reaches a certain level that is sufficient to overcome the elastic force of the reed blades themselves, the two reed blades will attract each other and come into contact.
Circuit Conduction: The contact of the reed blades causes the circuit to change from an open state to a closed state, enabling current to pass through and achieving the activation of the reed switch, thus realizing the on-off control of the circuit.
Hysteresis Phenomenon
Maintaining the Closed State: An interesting feature of reed switches is their hysteresis. Even when the magnetic field strength drops below the initial actuation level, the switch remains closed. Only when the magnetic field strength decreases to a certain lower threshold value will the reed blades demagnetize and separate, and the circuit will be disconnected.
Ferrite magnet:
Samarium cobalt magnet: