Industrial sensors are fundamental to every automation system. They provide the real-world data that PLCs need to make decisions, control processes, and ensure safety. Choosing the right sensor for an application requires understanding the different technologies available and their respective strengths and limitations.
Proximity Sensors
Proximity sensors detect the presence or absence of an object without physical contact. They are the most commonly used sensors in factory automation.
Inductive Proximity Sensors:
- Detect metallic objects only
- Typical sensing range of 2-30 mm
- Extremely reliable with no moving parts
- Ideal for position detection, counting, and end-of-travel sensing
Capacitive Proximity Sensors:
- Detect both metallic and non-metallic objects including liquids, powders, and plastics
- Useful for level detection through non-metallic container walls
- Slightly less reliable than inductive sensors in dusty environments
Photoelectric Sensors:
- Use light beams (visible or infrared) for detection
- Available in through-beam, retro-reflective, and diffuse configurations
- Much longer sensing ranges (up to several metres)
- Can detect transparent objects with specialised models
Temperature Sensors
Temperature measurement is critical in process industries:
- Thermocouples (TC): Wide temperature range (-200C to 1800C), robust, inexpensive. Types J, K, and T are most common in industrial applications
- Resistance Temperature Detectors (RTD): Higher accuracy than thermocouples, excellent stability. PT100 and PT1000 are industry standards
- Infrared sensors: Non-contact temperature measurement for moving objects or hazardous environments
Pressure Sensors
Industrial pressure sensors convert pressure into an electrical signal:
- Gauge pressure transmitters: Measure pressure relative to atmospheric pressure
- Absolute pressure transmitters: Measure pressure relative to perfect vacuum
- Differential pressure transmitters: Measure the difference between two pressure points, commonly used for flow measurement
Flow Sensors
Flow measurement technologies include:
- Electromagnetic flow meters: For conductive liquids, no moving parts, low maintenance
- Coriolis flow meters: Highest accuracy, measure mass flow directly
- Ultrasonic flow meters: Non-invasive, clamp-on options available
- Vortex flow meters: Good for steam and gas measurement
Sensor Selection Criteria
When selecting a sensor for your application, consider:
- Environmental conditions: Temperature, humidity, dust, chemical exposure
- Accuracy requirements: Repeatability, resolution, and total error
- Electrical interface: 4-20 mA, 0-10 V, digital (IO-Link, PROFINET)
- Protection rating: IP65 for general industrial, IP67/IP69K for washdown environments
- Certifications: ATEX/IECEx for hazardous areas, SIL ratings for safety applications
At EDWartens UK, our industrial automation courses include practical sensor selection and configuration exercises using real industrial sensors and PLC hardware.