9 Photoelectric Sensor Detection Modes You Should Know | Atonm Sensors

Photoelectric sensors operate in several detection modes: through-beam, retro-reflective, polarized retro-reflective, direct-reflective, wide-beam, focused, fixed-area and adjustable-area types. Note: do not confuse these with capacitive or inductive proximity switches. For fiber optic sensors, using separate fiber forms the through-beam mode; using direct and retro fibers forms proximity detection. Ultrasonic sensors have two modes: through-beam and proximity.

1. Through-beam (opposed mode)

The emitter and receiver are aligned so the emitter beam directly reaches the receiver. When an object blocks the beam, the sensor output changes to indicate detection. This is the earliest photoelectric detection mode.

2. Retro-reflective

In retro-reflective mode the sensor houses both emitter and receiver; light is sent to a reflector and returned to the receiver. When an object interrupts the returned beam, detection occurs. Effective range is measured from sensor to reflector and beam shape may vary depending on proximity and optics.

3. Proximity detection

Proximity mode detects energy reflected back from the object to determine presence. The emitter and receiver are on the same side. These modes include direct-reflective, wide-beam, focused, fixed-area and adjustable-area detection.

4. Direct-reflective

Direct-reflective sensors illuminate the object from multiple angles and rely on the portion of light reflected back to the receiver. Detection distance depends on object reflectivity; white surfaces yield longer ranges than dark surfaces.

5. Focused

Focused sensors add a lens to concentrate emitted light at a near focal point, creating a small high-energy detection zone. They detect small or low-reflectivity objects that wide-beam sensors may miss.

6. Fixed-area

Fixed-area sensors provide a clearly defined detection zone and ignore objects outside that zone, using comparison between two receiver inputs to determine presence.

7. Adjustable-area

Adjustable-area sensors allow the detection distance to be tuned. The receiver outputs two currents I1 and I2; their ratio changes with reflection position, and the switch threshold can be adjusted via a potentiometer.

8. Fiber optic

Fiber is not a single detection mode but enables various modes depending on fiber configuration, including focused lenses for probe heads.

9. Ultrasonic proximity mode

Ultrasonic transducers produce and receive sound waves; reflections are used to detect objects. Ultrasonic sensors are split into electrostatic and piezoelectric types. Electrostatic types support longer ranges (typically 6–7 m) for applications like tank level sensing; piezoelectric types are shorter range (~1 m) but more robustly sealed for harsh environments.