Reed Switch: Advantages and Disadvantages

This page explores the advantages and disadvantages of reed switches, outlining their benefits and drawbacks.

What is a Reed Switch? Introduction

• A reed switch is a magnetically activated mechanical switch.
• It consists of two metallic contacts enclosed in a small enclosure, typically a glass capsule.
• The contacts are magnetic and move in response to a magnetic field. A permanent magnet is needed to activate the switch.
• There are two main types of reed switches: SPST (Single Pole Single Throw) and SPDT (Single Pole Double Throw). The most common type is SPST, which can be either normally open or normally closed.

• A common everyday application of reed switches is in alarm systems. In this application, the reed switch and a magnet are mounted very close to each other on a door or window. Normally, the switch is closed. When the door or window opens, the switch opens, breaking the circuit and triggering the alarm.
• The figure above depicts the construction of a reed switch and its symbol.
• The physical size of the reed switch depends on its current switching capability.

Benefits or Advantages of Reed Switches

The following are the benefits and advantages of using reed switches:

• Simple Operation: Additional components are not needed for operation, except for a magnet.
• AC/DC Compatibility: It can switch both AC and DC.
• Voltage Switching Capability: It can switch voltages up to 200V in certain cases. Some variants can switch up to 500mA.
• Zero Power Consumption: It can be used by a magnet in an open or closed state indefinitely without any power consumption.
• Environmental Resistance: Its performance is not affected by dust or dirt, unlike optical switches.
• Activation Through Materials: It can be activated through non-magnetic materials such as plastic or paper.

Drawbacks or Disadvantages of Reed Switches

The following are the drawbacks and disadvantages of using reed switches:

• External Magnet Required: It requires a separate magnet for operation. Furthermore, it does not work satisfactorily when the magnet is more than a few millimeters away from the switch.
• Size Limitations: Reed switches cannot be miniaturized to the same extent as other surface mount chips.
• Fragility: The glass envelope can be easily damaged.
• Arcing: Arcing may occur between the contacts.
• Limited Sensing Material: Only ferrous objects can be used for sensing an object that comes between the switch and the magnet.
• Susceptibility to Magnetic Fields: It can be accidentally activated by other magnetic fields.
• Debouncing Required: It must be debounced when connected to a controller or logic chip.