The **21055-R** typically refers to a high-performance **Magnetic Proximity Sensor** or a **Reed Switch** assembly, often manufactured by companies like Littelfuse (Hamlin) or specific industrial sensor providers. These components are designed to detect the presence of a magnetic field to open or close an electrical circuit. --- ### 1. Key Technical Specifications The "R" suffix usually denotes "RoHS Compliance," meaning the part is manufactured without hazardous materials like lead. | Feature | Typical Specification | | :--- | :--- | | **Contact Form** | Form A (Normally Open) or Form C (Changeover) | | **Switching Voltage** | Up to 200V DC | | **Switching Current** | 0.5A to 1.0A | | **Power Rating** | 10W - 20W | | **Operating Temp** | -40°C to +105°C | | **Housing Material** | Glass-reinforced Plastic or Stainless Steel | --- ### 2. Internal Electronic Components The 21055-R series is a passive electronic device, meaning it does not require a power source to operate its internal mechanism. * **Hermetically Sealed Reed Switch:** The core component consists of two ferromagnetic blades (reeds) encased in a glass envelope filled with inert gas. This prevents oxidation and allows for millions of switching cycles. * **Contact Plating:** The tips of the internal reeds are usually plated with **Rhodium** or **Ruthenium**. These precious metals ensure low contact resistance and prevent "sticking" under electrical loads. * **Encapsulation:** The internal glass switch is potted in an epoxy resin within the outer shell to protect it from mechanical shock, vibration, and moisture. --- ### 3. Operational Logic The part operates based on **magnetic induction**: 1. **Resting State:** The reeds are physically separated; the circuit is "Open." 2. **Actuation:** As a permanent magnet approaches the 21055-R, the reeds become polarized and attract each other. 3. **Connection:** The reeds touch, closing the circuit and allowing current to flow. --- ### 4. Common Applications Due to its contactless nature, the 21055-R is used in environments where dirt, dust, or liquids would ruin a standard mechanical switch: * **Security Systems:** Door and window position sensing. * **Industrial Automation:** Limiting switch for hydraulic cylinders or robotic arms. * **Automotive:** Seatbelt buckle detection and fluid level sensing. * **Appliances:** Detecting if a lid is closed (e.g., washing machines).