Photo Prox
Detects the presence of an object by a change in received light. Through-beam, retro-reflective and diffuse-reflective arrangements use different emitter, receiver and target geometries; the rated distance belongs to the chosen model and sensing method.
A modulated (typically 5–50 kHz) LED produces a bright IR or red emission; a photodiode at the detector synchronously demodulates received light to reject ambient/sunlight bias. A peak detector and Schmitt comparator with hysteresis output a digital ON/OFF when received light crosses a threshold. AGC and a teach-in button calibrate sensitivity to the application's specific reflectivity at install.
In plain terms
Like the laser tripwires in a heist movie — invisible until something crosses them, and the alarm fires the moment the beam path changes.
Why designers use it
- Detecting object presence without mechanical contact.
- Choosing an optical arrangement suited to the target, mounting and required distance.
- Using a rated sensing distance that includes the manufacturer's defined target and operating conditions.
Best for
- Conveyor sensing
- Counting
- Garage doors
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- Through reflective or transparent targets — glass and clear plastic don't trigger diffuse sensors; pull a transparent-target-rated colour or laser sensor.
- In dusty, oily, or splashing environments — the lens fouls and sensitivity drops; pull capacitive or inductive sensors.
Common mistakes
- Forgetting that bright sun-lit retro-reflective tape becomes the brightest 'object' in view — the chip stops triggering on actual objects.
- Routing the cable in a flexible carrier without a ferrite — high-frequency switching modulates pickup and the comparator chatters.
Where you will find it
- An illustrative through-beam arrangement places an emitter and receiver on opposite sides of an object's path; interrupting the beam changes the detected state.
- Omron distinguishes rated sensing distances and test objects for different optical arrangements. A generic sensor example does not establish a garage-door safety system's response time or certification.
A short history
A photoelectric sensor detects objects using an emitter and a light receiver. Depending on its arrangement, it senses an interrupted beam or light returned from a target. This is useful for contactless detection on machinery, but target reflectivity and transparency affect which sensing arrangement will work.