Photoelectric sensor

01

Choose the sensing mode for the target and mounting

Keyence classifies photoelectric sensors by detection method. Through-beam sensors detect a target crossing the axis between a separate transmitter and receiver, giving long detecting distance, a stable detecting position and detection of opaque objects regardless of shape, colour or material. Retroreflective sensors bounce the beam off a reflector, saving space and wiring on one side and reaching further than diffuse types. Diffuse-reflective sensors need only the sensor unit and no axis alignment, and can detect reflective transparent objects and distinguish colour. Focused-beam, small-spot definite-reflective and fixed-distance types detect minute objects or marks, ignore the background and handle targets of varying reflectance, and luster-recognition types detect transparent targets regardless of colour. [1]

Keyence also distinguishes self-contained sensors, with setup and indicators on the unit, from separate-amplifier types whose smaller heads mount more flexibly, and plastic housings, lighter but weaker, from metal housings such as stainless steel that are more robust and longer-lived. [2]

Give the supplier the target (material, colour, transparency, size, speed), mounting distance and whether a reflector or separate receiver can be fitted, background behind the target, required response time, output (PNP/NPN, IO-Link) and supply voltage, connection (cable or M8/M12 connector), housing size and material, IP rating and washdown, operating temperature, and quantity.

02

Size the range, response time and housing

Banner's photoelectric selection table shows how range changes with mode. Its QS18 series is rated 20 m opposed, 6.5 m non-polarized and 3.5 m polarized retroreflective, 10 m laser polarized retroreflective, 600 mm diffuse, 150 mm fixed-field and 350 mm adjustable-field, with 600–800 µs response, IP67 and −20 to +70 °C. Its QS30 reaches 60 m opposed and 1,400 mm diffuse at 2,000–5,000 µs; its T18-2 offers IP67, IP68 and IP69K with −40 to +70 °C; and its metal-housed laser Q3X responds in 250 µs with 300 mm diffuse range and IP69K. Some series offer IO-Link and clear-object detection. [3]

Editorial calculation: in the QS18 series the 20 m opposed range is about 6 times the 3.5 m polarized retroreflective range and about 33 times the 0.6 m diffuse range. A target on a conveyor moving at 1 m/s travels 0.6–0.8 mm during the QS18's 600–800 µs response and 2–5 mm during the QS30's 2,000–5,000 µs, which matters when detecting small gaps or edges. [3]

03

Check the product standard and its photoelectric switch types

IEC 60947-5-2, Low-voltage switchgear and controlgear – Part 5-2: Proximity switches, covers inductive, capacitive, ultrasonic, photoelectric and non-mechanical magnetic proximity switches; photoelectric proximity switches are those that sense the presence of objects. The 2007 third edition described them as self-contained devices with semiconductor switching elements for circuits whose rated voltage does not exceed 250 V 50/60 Hz AC or 300 V DC, and did not cover switches with analogue outputs. The fourth edition of 2019 replaced the 2007 edition and its 2012 amendment; its listed changes include new definitions and test procedures for photoelectric proximity switches of type D with background suppression, updated construction requirements including artificial optical radiation, changes to the sensing range and operating distance specifications, and updated EMC requirements. [4] [5]

The background-suppression mode and the range tables described above by Keyence and Banner sit under this standard; ask which edition the sensor is tested to, since background-suppression requirements were added in 2019. [1] [3] [2]

Editorial calculation: a 24 V DC sensor is well inside the 300 V DC limit of the 2007 scope; a 240 V AC self-contained sensor is within 250 V AC, but anything above that falls outside this part.

Ask the supplier for the declaration of conformity naming IEC/EN 60947-5-2 and its edition, the sensing-range test conditions and, for background-suppression sensors, whether they were tested as type D under the 2019 edition.

04

Compare what suppliers offer

Suppliers linked to this page list photoelectric sensors; each card links to the page reviewed.

Listings include cylindrical M18 and rectangular photoelectric sensors, slot types, background-suppression and colour-mark sensors, high-temperature types and infrared emitter and receiver components; ask each for the range by mode on a standard target, response time, output type and IP rating.

05

Trace the sensor construction

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your sensor

A photoelectric sensor quotation needs values for your application. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the target, mounting and environment together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Target: [material; colour; transparency; size; speed]
Mounting: [distance; reflector or receiver possible; background]
Performance: [response time; repeatability]
Electrical: [supply; PNP/NPN; IO-Link]
Connection: [cable or M8/M12]
Environment: [IP; washdown; temperature]
Quantity: [units]

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