Reed switches, as magnetic sensors widely used in electronic devices and control systems, come in various types to meet different application requirements. Selecting the appropriate reed switch correctly is crucial for ensuring the performance and reliability of the system.
I. Types of Reed Switch
(I) Classification by Contact Form
♦Normally Open (NO) Type
The normally open reed switch has its contacts in an open state when there is no magnetic field. When an external magnetic field approaches and reaches a certain intensity, the contacts close and the circuit conducts. For example, in some door and window sensors, when the door or window is closed, the magnet approaches the normally open reed switch, causing it to close and triggering the alarm system or other related devices to inform the user of the change in the door or window status.
♦Normally Closed (NC) Type
The normally closed reed switch is the opposite. When there is no magnetic field, the contacts are closed and the circuit is conducting. Once a magnetic field approaches, the contacts open and the circuit is disconnected. This type of reed switch is often used in liquid level sensors. When the liquid level rises and the magnetic float brings the magnetic field close to the normally closed reed switch, the switch opens to stop further liquid injection and achieve liquid level control.
♦hangeover (CO) Type
The changeover reed switch has a common contact and two normally closed and normally open contacts. When there is no magnetic field, the common contact is connected to the normally closed contact; when a magnetic field acts, the common contact switches to connect to the normally open contact. It can realize different circuit connection methods depending on the presence or absence of a magnetic field and is more commonly used in some circuits that require multiple control logics. For example, in some complex automated control systems, different circuit functions can be switched according to different magnetic field signals.
(II) Classification by Packaging Form
♦Glass Encapsulated Type
The glass encapsulated reed switch is a common type. It seals the reed inside a glass tube, and the glass tube plays a role in protecting the reed and providing a stable working environment. The advantage of this packaging form is its good insulation and sealing performance, which can effectively prevent the influence of the external environment on the reed, such as dust and moisture. At the same time, the glass encapsulated reed switch is usually small in size and suitable for electronic devices with high space requirements, such as small sensors and magnetic field detection function modules in mobile devices like mobile phones.
♦Plastic Encapsulated Type
The plastic encapsulated reed switch encapsulates the reed in a plastic housing. This packaging method can improve the mechanical strength of the reed switch to some extent, making it more resistant to shock and vibration. The plastic encapsulated reed switch may have better resistance to environmental stress compared to the glass encapsulated type and is suitable for use in some harsher environments. For example, in industrial control equipment that may be subject to a certain degree of mechanical impact or vibration, but where the insulation performance requirements are not particularly high.
(III) Classification by Reed Material
♦Nickel-Iron Alloy Reed Type
Nickel-iron alloy is one of the commonly used reed materials in reed switches. This material has good magnetic and mechanical properties, can respond sensitively under the action of a magnetic field, and has a certain degree of elasticity and strength to ensure the reliable closing and opening of the contacts. The nickel-iron alloy reed type reed switch is suitable for general magnetic field detection and control applications, such as simple position sensors and proximity switches, and is widely used in consumer electronics and home appliances.
♦Other Special Material Reed Types
In addition to nickel-iron alloy, some reed switches use reeds made of special materials to meet special requirements. For example, for some applications that need to work in a high-temperature environment, a high-temperature resistant alloy material may be used as the reed to ensure that it can still maintain good magnetic and mechanical properties under high-temperature conditions. In some applications with extremely high requirements for magnetic field sensitivity, such as weak magnetic field detection in medical equipment and high-precision magnetic field measuring instruments, reeds made of materials with higher magnetic permeability should be preferentially considered to ensure accurate detection of weak magnetic field changes and meet the high-precision requirements of the equipment.
II. Selection Method of Reed Switch
(I) Selecting the Contact Form According to the Application Scenario
1.Signal Detection and Triggering Scenario
If the application scenario is mainly to detect the position and motion state of an object and needs to trigger a signal when the object reaches a specific position or state changes, the normally open or normally closed reed switch may be more appropriate. For example, in the material position detection on an automated production line, when the material reaches the specified position, the normally open reed switch closes and sends a signal to the control system to start the next processing operation.
2.For some complex scenarios that need to switch different circuit functions according to the presence or absence of a magnetic field, such as the intelligent lighting system that controls the on/off and brightness adjustment of the lights according to the signals of the light sensor and the human proximity sensor, the changeover reed switch can better meet the requirements.
Safety Protection and Control Scenario
3.In terms of safety protection, such as in a fireproof door monitoring system, the normally closed reed switch is often used to monitor the closed state of the door. When the door is normally closed, the switch is closed and the circuit is conducting, indicating a safe state; once the door is opened and the magnetic field moves away from the normally closed reed switch, the switch opens and triggers an alarm signal to remind relevant personnel of potential safety hazards.
(II) Considering the Working Environment to Select the Packaging Form
a.Application in Ordinary Environments
In general indoor environments, such as smart home devices and office electronic devices, the requirements for the mechanical strength and environmental adaptability of the reed switch are not particularly high, and the glass encapsulated reed switch usually can meet the requirements. Its good insulation performance and small size can adapt to the compact design and normal working environment of these devices.
b.Application in Harsh Environments
For industrial environments, especially those with more dust, moisture, vibration, or impact, such as automated equipment in factory workshops and outdoor electronic monitoring equipment, the plastic encapsulated reed switch may be a better choice. Its stronger mechanical strength and relatively good resistance to environmental stress can ensure stable operation under harsh conditions.
(III) Selecting the Reed Material According to the Performance Requirements
Conventional Performance Requirements
If the application has relatively conventional performance requirements for the reed switch, such as the magnetic field detection function in most consumer electronics and home appliances, the nickel-iron alloy reed type reed switch is sufficient to meet the requirements. It can provide reliable performance and has a relatively reasonable cost, which can control the production cost while ensuring the product function.
Special Performance Requirements
When the application needs to work stably for a long time in a high-temperature environment, such as sensors in the engine compartment of a car and detection equipment near industrial furnaces, a reed switch with a reed made of a special high-temperature resistant material should be selected. In applications with extremely high requirements for magnetic field sensitivity, such as weak magnetic field detection in medical equipment and high-precision magnetic field measuring instruments, the reed switch with a reed made of a material with high magnetic permeability should be given priority to ensure accurate detection of weak magnetic field changes and meet the high-precision requirements of the equipment.
Selecting the appropriate reed switch requires comprehensive consideration of various factors such as the application scenario, working environment, and performance requirements. Only by selecting the correct type of reed switch according to specific needs can its role in electronic devices and control systems be fully exerted and the efficient, stable, and reliable operation of the system be ensured.
