## Overview of the OMRON E3JK-R2M1/R2M2 The **E3JK-R2** is a popular industrial **Retro-reflective Photoelectric Sensor** manufactured by OMRON. It is widely used in automation for object detection because it combines the emitter and receiver into a single housing, requiring a reflector on the opposite side to function. --- ### 1. Key Technical Specifications | Feature | Specification | |:---|:---| | **Sensing Method** | Retro-reflective (requires a reflector) | | **Sensing Distance** | Typically 2.5 meters to 5 meters (depending on reflector used) | | **Supply Voltage** | 24 to 240 VAC or 12 to 240 VDC (Universal Voltage) | | **Output Type** | Relay Output (SPDT) - 3A at 250 VAC | | **Response Time** | 30 ms maximum | | **Light Source** | Infrared LED (950 nm) or Red LED (depending on specific sub-model) | | **Operation Mode** | Light-ON / Dark-ON (selectable by wiring/switch) | --- ### 2. Internal Electronic Components The E3JK-R2 is known for its "built-in power supply" design, meaning it contains several internal stages to handle high-voltage AC or DC: 1. **Power Supply Circuit:** Uses a switching regulator or a capacitive dropper circuit to step down the 240V input to low-voltage DC (typically 12V or 5V) to power the internal logic. 2. **Oscillator/Emitter:** Drives the LED (Infrared or Red) to pulse light at a specific frequency to avoid interference from ambient sunlight. 3. **Photodetector & Amplifier:** A photodiode or phototransistor receives the reflected light. The signal is then filtered (to match the emitter's frequency) and amplified. 4. **Comparator/Logic:** A logic circuit determines if the beam is broken. If the light intensity drops below a certain threshold, it triggers the output. 5. **Mechanical Relay:** Unlike NPN/PNP sensors that use transistors, the E3JK-R2 uses a physical **Electromagnetic Relay**. This allows it to switch high-current AC loads directly. --- ### 3. Wiring Configuration The sensor typically uses a 5-wire cable system. Below is the standard pinout for the relay output version: | Wire Color | Function | Description | |:---:|:---|:---| | **Brown** | Power (L/+) | 24 - 240 V AC/DC | | **Blue** | Power (N/-) | 24 - 240 V AC/DC | | **White** | Relay Common (COM) | The "Pole" of the switch | | **Black** | Normally Open (NO) | Closes when object is detected (in Dark-ON) | | **Gray** | Normally Closed (NC) | Opens when object is detected (in Dark-ON) | --- ### 4. Advantages and Limitations * **Pros:** * **Universal Voltage:** Can be used in almost any electrical environment globally. * **High Load Capacity:** The relay output can drive small motors or contactors without an external interface. * **Easy Alignment:** Only one side needs wiring; the other side is just a plastic reflector. * **Cons:** * **Relay Wear:** Mechanical relays have a finite lifespan (approx. 100,000 operations under load). * **Slow Speed:** 30ms response is much slower than solid-state (transistor) sensors, making it unsuitable for high-speed counting. ---