The **FCR-D2-R** is an electronic logic and relay output module typically used in Building Management Systems (BMS), specifically for controlling fan coil units (FCUs). It acts as an interface between a controller (like a thermostat or PLC) and the mechanical components of an HVAC system. --- ### 1. Technical Specifications The following table outlines the primary electronic characteristics of the FCR-D2-R: | Feature | Specification | | :--- | :--- | | **Input Voltage** | 24V AC/DC (±10%) | | **Output Type** | Relay Contacts (Volt-free/Dry contacts) | | **Relay Rating** | 5A / 230V AC (Resistive) | | **Control Inputs** | 0-10V DC or Binary/Step Logic | | **Mounting** | DIN Rail (35mm) | | **Function** | 3-Speed Fan Control + 2-Point Valve Control | --- ### 2. Core Electronic Components #### A. Relay Logic Board The unit contains high-quality miniature relays. These are electromagnetically operated switches that allow a low-power signal (24V) to control high-power loads (230V fan motors). * **Interlock Mechanism:** The internal circuitry usually includes electrical interlocking to ensure that "Low," "Medium," and "High" speeds cannot be energized simultaneously, preventing motor burnout. #### B. Signal Conversion (DAC) If the FCR-D2-R is used in 0-10V mode, it contains an **Analog-to-Digital Converter** or a comparator circuit. It interprets the voltage level and triggers the corresponding relay: * **0-2V:** All Off * **2-5V:** Low Speed * **5-8V:** Medium Speed * **8-10V:** High Speed #### C. Terminal Interface The module uses screw terminals for secure electronic connections: * **Power Terminals:** G and G0 for the 24V supply. * **Input Terminals:** For the control signal (Y). * **Output Terminals:** Common (C) and normally open (NO) contacts for Fan speeds and Valve actuators. --- ### 3. Application Wiring Logic The FCR-D2-R is designed to bridge the gap between a modern electronic controller and older mechanical fan motors. ```mermaid graph LR A[Controller 0-10V] --> B(FCR-D2-R Module) B --> C[Fan Speed 1] B --> D[Fan Speed 2] B --> E[Fan Speed 3] B --> F[Heating/Cooling Valve] ``` --- ### 4. Safety and Protection * **Galvanic Isolation:** The module provides isolation between the control electronics (BMS side) and the power electronics (Motor side), protecting the controller from voltage spikes. * **Housing:** Usually made of self-extinguishing polycarbonate (UL94-V0) for fire safety in electrical cabinets.