Reed Magnet Detection Switch

Reed Magnet Detection Switch (SPST-NO) is a simple yet incredibly reliable electromechanical component that utilizes a magnetic field to perform switching operations. This fundamental technology involves two ferromagnetic reeds hermetically sealed within a glass envelope, which protects the contacts from external contaminants like dust and moisture. When you bring a permanent magnet near the sensor, the magnetic field causes the two reeds to pull together, thereby closing the circuit and switching the device ON. Therefore, the reed switch is a non-contact sensor that offers ultra-low power consumption and an exceptionally long operational life, making it a critical sensor in countless industrial and consumer products. Furthermore, its simple two-pin design and passive operation allow easy integration into complex electronic systems, enhancing both safety and functionality.

Key Features:

• Hermetically Sealed Contacts: The contacts are encased in a glass tube filled with an inert gas, which completely protects them from dust, moisture, and corrosive environments, ensuring high reliability.
• Zero Standby Power: The switch requires zero operating power for contact closure, as the permanent magnet provides the actuation force.
• High Reliability and Longevity: Since the contacts operate without mechanical wear, they feature an extremely long lifespan, often reaching billions of operations under low-load conditions.
• Low Contact Resistance: When closed, the switch offers very low internal resistance (typically less than 150 mΩ), ensuring minimal signal loss.
• Versatile Voltage Handling: You can use the switch with both DC and low-current AC circuits, accommodating a wide range of control voltages.

Technical Specifications (Typical):

• Contact Form: SPST-NO (Single Pole, Single Throw, Normally Open)
• Max. Switching Voltage: Up to 200 VDC / 140 VAC
• Max. Switching Current: Up to 0.5 A
• Max. Switching Power: 10 W / 10 VA max (VDC x Amps ≤ 10)
• Initial Contact Resistance: ≤ 150 mΩ
• Insulation Resistance: ≥ 10⁹ Ω (Typically 10¹¹ to 10¹² Ω)
• Actuation Sensitivity (Pull-In): 10 to 60 AT (Ampere-Turns) typically, depending on model
• Operating Temperature Range: −40°C to +125°C

Mechanical Specifications:

• Housing Material: Hermetically sealed glass envelope
• Contact Material: Rhodium or Ruthenium plated ferromagnetic reeds (NiFe alloy)
• Package Style: Axial Leads (Through-Hole)
• Environmental Sealing: Excellent resistance to dust, moisture, and corrosion (IP67 when mounted in an enclosure)

Dimensions (Typical Miniature Reed):

• Glass Length: ≈ 10.0 mm to 14.0 mm
• Glass Diameter: ≈ 1.8 mm to 2.2 mm
• Lead Material: Tin-plated Nickel Iron
• Total Overall Length: Varies significantly based on lead length (≈ 40 mm to 60 mm total)

Pinout and Wiring:

• Pin 1 (Lead 1): Connect to one side of the signal or power line.
• Pin 2 (Lead 2): Connect to the other side of the load or microcontroller input pin.
• Wiring Note (Normally Open – NO): The switch functions as a simple mechanical contact. You should wire it in series with the load and power source. When a magnet is present, the contacts close, and the circuit becomes complete. Consequently, you must use a current-limiting component (like a series resistor) or drive a small load (like a transistor gate) to protect the contacts from high inrush currents.

Datasheet Reference:

• Download Littelfuse MITI-7L Reed Switch Datasheet (Representative)

Commonly Used in:

• Proximity Sensors: Core component in proximity and position sensing modules.
• Security Systems: Used extensively in door and window alarms (magnetic contacts).
• Reed Relays: The switch element within a reed relay, which an electromagnetic coil actuates.

Applications:

• Level Sensing: Detects the level of fluids using a magnet floating on the liquid surface.
• Limit Switching: Indicates the end-of-travel or home position in pneumatic cylinders and small actuators.
• Flow Metering: Counts rotations in water or gas meters by sensing a rotating magnet.
• Appliance Safety: Detects the closing of appliance doors (e.g., refrigerators, washing machines) to initiate or stop operation.

Equivalent Models:

• MDRR Series: Many manufacturers produce the MDRR series, offering similar specifications and performance in a standard package.
• MITI Series (Littelfuse): A wide family of miniature reed switches that share the core switching principle.
• MATE Series: Another common designation for axial-leaded, magnetically actuated switches.

Package Includes:

• 1 x Reed Magnet Detection Switch (SPST-NO)