The **31PD-R** is a specific model of a **Photoelectric Retro-reflective Sensor**, typically used in industrial automation for object detection. It belongs to a class of sensors that combine a transmitter and a receiver in a single housing, requiring a reflector to operate. --- ### 1. Technical Specifications Below are the typical electronic characteristics and parameters for the 31PD-R series: | Feature | Specification | | :--- | :--- | | **Sensing Type** | Retro-reflective (requires a corner-cube reflector) | | **Operating Voltage** | 12–240V DC / 24–240V AC (Multi-voltage) | | **Sensing Distance** | Typically 0.1 to 4 meters (varies by reflector size) | | **Output Type** | Relay Output (SPDT - Single Pole Double Throw) | | **Response Time** | < 20ms | | **Current Consumption** | < 2W | | **Light Source** | Infrared LED (non-visible) or Red LED | --- ### 2. Key Internal Components The 31PD-R is composed of several critical electronic sub-assemblies: * **Emitter (IR LED):** Pulses a beam of light toward a remote reflector. * **Receiver (Phototransistor):** Detects the light bouncing back from the reflector. If an object breaks this beam, the sensor triggers. * **Relay Module:** Unlike NPN/PNP sensors, the "R" in the suffix usually denotes a **Relay output**, allowing it to switch higher AC/DC loads directly. * **Potentiometer:** An adjustable screw used to calibrate the sensitivity (sensing distance). * **Status Indicators:** Usually features a Green LED (Power) and a Yellow/Red LED (Output state). --- ### 3. Wiring Diagram Logic Because the 31PD-R is a multi-voltage relay sensor, the wiring typically involves 5 wires: | Wire Color | Function | Description | | :--- | :--- | :--- | | **Brown** | Power (L/+) | Connection to Power Source | | **Blue** | Power (N/-) | Connection to Power Source | | **White** | Common (COM) | Relay common terminal | | **Black** | Normally Open (NO) | Closes when an object is detected | | **Gray** | Normally Closed (NC) | Opens when an object is detected | --- ### 4. Operational Principles 1. **Alignment:** The sensor and reflector must be aligned. The sensor emits light; the reflector sends it back to the receiver. 2. **Detection:** When an opaque object passes between the sensor and the reflector, the light path is broken. 3. **Output Switching:** The internal logic circuit de-energizes (or energizes) the relay, toggling the NO/NC contacts to signal a PLC or motor starter. ---