The **LC-21-R** is a specific model of a photoelectric beam sensor, typically used in security systems, garage doors, and industrial automation for perimeter detection. It functions as a single-beam infrared (IR) sensor set consisting of a transmitter and a receiver. ### 1. Core Electronic Components The device is split into two main physical units: the **Emitter (TX)** and the **Receiver (RX)**. | Component | Description | Function | | :--- | :--- | :--- | | **Infrared LED** | Located in the Transmitter (TX). | Emits a modulated, invisible beam of light at a specific wavelength (usually 940nm). | | **Photodiode/Transistor** | Located in the Receiver (RX). | Detects the incoming IR light from the transmitter. | | **Relay (SPDT)** | Output component in the Receiver. | Provides a Dry Contact output (Common, NO, NC) to trigger alarms or controllers. | | **Modulator/Oscillator** | Integrated Circuit (IC). | Pulses the IR light at a high frequency to prevent interference from sunlight or house lights. | | **Status LEDs** | Indicator lights. | Usually Red (Alarm/Power) and Green (Alignment) to assist in installation. | --- ### 2. Technical Specifications Understanding the electronic limits is crucial for installation and troubleshooting. * **Input Voltage:** 12V to 24V DC/AC (Universal power input). * **Current Consumption:** TX: ~15mA | RX: ~30mA. * **Wavelength:** 940nm (Near-Infrared). * **Output Capacity:** 1A max at 36V (Relay contact). * **Detection Range:** Typically up to 15-20 meters (outdoors) or 30 meters (indoors). --- ### 3. Wiring Diagram Overview The wiring usually involves a 2-wire connection for the Transmitter and a 4-to-5 wire connection for the Receiver. ```text Transmitter (TX): [ V+ ] --- (+) 12-24V [ V- ] --- (-) GND Receiver (RX): [ V+ ] --- (+) 12-24V [ V- ] --- (-) GND [ NC ] --- Alarm Loop (Normally Closed) [COM ] --- Common [ NO ] --- Optional (Normally Open) ``` --- ### 4. Key Electronic Features * **Aspherical Lens:** The optics focus the IR beam into a narrow path to increase the range and sensitivity. * **Anti-Interference Filter:** The receiver includes a filter that blocks visible light spectrums, allowing only the 940nm IR frequency to pass. * **Alignment Adjustment:** The PCB is often mounted on a swivel or has adjustable screw points to physically align the beam without moving the entire housing.