The **PLC-RSP-24UC/21** (manufactured by Phoenix Contact) is a narrow, 6.2 mm wide relay module designed for industrial automation. It is a "PLC-Interface" relay, meaning it acts as an intermediary between a controller (like a PLC) and high-power field devices. --- ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Input Voltage ($U_N$)** | 24 V AC/DC | | **Contact Type** | 1 PDT (Single Pole, Double Throw / Changeover) | | **Contact Material** | AgSnO (Silver Tin Oxide) | | **Max Switching Voltage** | 250 V AC/DC | | **Limiting Continuous Current** | 6 A | | **Housing Width** | 6.2 mm | | **Connection Method** | Spring-cage connection (RSP) | --- ### 2. Internal Electronic Components The module consists of two main parts: the **Relay Base** and the **Pluggable Miniature Relay**. #### A. Input Circuit (Coil Side) * **Bridge Rectifier:** Because the device is rated for "UC" (Universal Current), it contains internal rectification. This allows the relay to operate on either 24V AC or 24V DC without polarity concerns. * **LED Indicator:** A yellow LED is integrated into the base to provide a visual status of the switching state. * **Damping/Suppression Diode:** Protects the PLC output from inductive voltage spikes (back-EMF) when the relay coil is de-energized. #### B. Output Circuit (Contact Side) * **Mechanical Contacts:** Uses a Single Pole Double Throw (SPDT) configuration. When the coil is energized, the common terminal (11) moves from the Normally Closed (NC, 12) to the Normally Open (NO, 14) position. * **AgSnO Contacts:** This material is used for its high resistance to welding and erosion, making it suitable for switching inductive loads. --- ### 3. Wiring Diagram Representation The following block represents the logical flow of the electronic path: ```text Input (A1, A2) --> Rectifier/Protection --> Coil (Inductive) | [Mechanical Linkage] | Output (11, 12, 14) <------------------- Changeover Contact ``` --- ### 4. Advantages of the RSP Series 1. **Space Efficiency:** The 6.2mm width allows for high-density mounting on DIN rails. 2. **Spring-Cage Connection (RSP):** Provides vibration-resistant wiring, ensuring the electronic connection remains stable in harsh environments compared to traditional screw terminals. 3. **Isolation:** Provides galvanic isolation between the low-voltage control logic (PLC) and the high-voltage load.