Digital input devices for Programmable Logic Controllers (PLCs) are essential components in industrial automation and control systems. These devices provide binary (on/off) signals to the PLC, which can be used to monitor the state of various processes and equipment. Here is a list of common digital input devices used with PLCs:
1. **Push Buttons**: Manually operated switches that can start or stop a process.
2. **Limit Switches**: Mechanically operated switches used to detect the presence or position of an object.
3. **Proximity Sensors**:
- **Inductive Proximity Sensors**: Detect metal objects without physical contact.
- **Capacitive Proximity Sensors**: Detect both metallic and non-metallic objects.
- **Ultrasonic Sensors**: Use sound waves to detect objects and measure distances.
4. **Photoelectric Sensors**: Use light beams to detect the presence or absence of objects.
- **Through-Beam Sensors**: Consist of a separate emitter and receiver.
- **Retro-Reflective Sensors**: Use a reflector to bounce light back to the receiver.
- **Diffuse Reflective Sensors**: The emitter and receiver are housed together, and the sensor detects light reflected off the object.
5. **Encoders**: Provide position or speed feedback by generating a series of electrical pulses.
- **Rotary Encoders**: Measure rotation, angle, or position.
- **Linear Encoders**: Measure linear displacement.
6. **Toggle Switches**: Manually operated switches that maintain their position until changed.
7. **Selector Switches**: Allow the selection of different circuit paths or functions.
8. **Reed Switches**: Magnetically operated switches used for position sensing.
9. **Float Switches**: Used to detect the level of liquid in a tank or vessel.
10. **Pressure Switches**: Detect pressure levels in gases or liquids and provide an on/off signal.
11. **Temperature Switches**: Provide signals based on temperature thresholds.
12. **Foot Switches**: Pedal-operated switches commonly used in machine tools.
13. **Magnetic Sensors**: Detect magnetic fields and are used for position or proximity sensing.
14. **Safety Light Curtains**: Provide a protective barrier by detecting objects in the path of a light beam array.
15. **Barcode Readers/Scanners**: Read and decode barcodes, often used in inventory management and logistics.
These devices convert various types of physical phenomena (e.g., position, presence, level, pressure) into electrical signals that the PLC can interpret and act upon, facilitating automated control and monitoring in industrial environments.