Technical Guide for Photoelectric Sensors

1. What is Photoelectric Sensor

  • Photoelectric sensors detect presence of an object without contact, using light reflection.
    They make an output signal according to an amount of received light that is reflected from a detection target.
    They are mainly used to contribute to automation and labor-saving at manufacturing factories.

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2. Main Features

  • Detection without contact
  • Detection in long distance
  • Detection of small objects
  • Detection regardless of materials
  • Fast response time
  • Dirt on lens with liquid or dust

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3. How to select a photoelectric sensor

Purpose and condition To be considered Applicable sensors
Selection by detection Positioning by detection of presence - Positioning accuracy
- Easy installation
- Through-beam
- Laser
Small-object detection - Small spot sizes
- Adjustable sensitivity
- Fiber
- Laser
Detection of fast-moving objects - Short response time - Fiber
Transparent-object detection - High-sensitivity/retro reflective - Transparent-object detection
Detection of surface unevenness - Small hysteresis - Diffuse reflective
- Displacement
Color mark detection - Colors of color mark, background and sensor light
- Short response time
- Color mark detection
- Fiber
Color contrast detection - High resolution - Mark sensor
Detection of less influenced by color differences - High-resolution receiver element - Laser BGS
Selection by installation location Small space - Small sizes - Fiber
- Miniature, Head-on/side-on
Installation on one side - Diffuse reflective, Limited diffuse reflective
Reflection from background - Small hysteresis - BGS
Influence from ambient illuminance Wider resistance against ambient illuminance - Laser
Robustness - Resin filled
- Metal housing
Location with water - High water resistance - IP67, IP69K

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4. Sensor structures

Type Detection method Description Popular models
Through-beam - Each of emitter and receiver units are used in a pair.
- As an amount of received light is comparably larger, it is less influenced from dust in environment.
Retro reflective - A pair of sensor and reflector is used.
- These require less installation space and wiring, compared with through-beam sensors.
Diffuse reflective - A single unit of sensor detects light reflection from a detection object.
- These require less installation space and wiring.
Wide-angle diffuse reflective - A wider aperture angle is equipped to detect a small difference in received light amount. These are suitable to detect an object of transparent and with slit. Z3D-W20N
Back Ground Suppression - A light receiving element of PSD or C-MOS is used to make an output upon detection at a preset distance. Detection of these models are less influenced from colors and materials of an object. BGS-HL05T
Transparent-object detection - A pair of sensor unit with a low hysteresis and reflector detects a small difference in received light amount. These are suitable to detect a transparent object, such as a film and glass. DR-Q400TN
Separate amplifier - A combination of sensor unit and amplifier can be selected according to application requirements.
- Various detection configurations can be set on an amplifier.
Fiber unit - An optical fiber is used to transfer light from and to an amplifier. NF-DB01
Fiber amplifier - A combination of fiber unit and amplifier can be selected according to application requirements.
- Small dimensions of fiber unit makes its installation possible in a small space. Combinations of various models can be made, even for detection of a color, height gap and liquid level.
Color mark detection - High resolution sensors can detect subtle color differences and color contrast. DM-18TN

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5. Glossary of photoelectric sensors

Term Description Term Description
Sensing distance Through-beam
The distance between an emitter and receiver.
Light ON An output turns on, when a received light amount reaches a certain level.
Retro reflective
The distance between a sensor and reflector.
Dark ON An output turns on, when a received light amount is below a certain level.
Diffuse reflective
The distance between a sensor and standard detection object.
Laser off input An external input can be used to stop light emittance of the sensor.
Smallest detection object Smallest sizes of object that can be detected by a sensor.
External input Output of a sensor can be made, according to status of an external input.
Response time Time to turn on or off an output, according to presence of an object.
Teach setting of a sensor can be triggered by an external input.
Hysteresis A distance between a point that a reflective sensor makes an output on a standard detection object and, then, a point that it turns the output off.
Off-delay timer An output is held for a preset time.
The function can be combined with controller programs.
Repeat accuracy A variation range in which a sensor performs detection.

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6. Glossary of fiber sensors

Term Description Term Description
Array Fiber cores are aligned in a line to emit light in a flat beam.
It is suitable to detect objects with unstable reflection, due to not fixed passages or uneven shapes.
There are also Screen types of fiber unit in a similar structure.
Limited diffuse reflective This fiber unit is used to make detection within a limited distance.
Light axises of emitter and receiver are set at angles to make detection within their crossing area.
Liquid level detection The fiber units are used for liquid level control.
There are contact types that detect a level by contact and pipe-installed types to be installed on a transparent pipe to make detection.
Fine fiber Fiber cores with diameters of less than 0.5mm are called as a fine fiber.
A thin light axis through fine fiber makes detection of a small object easy, but in a short detection distance.
Flexible A fiber unit that does not get broken, even when it is bent in a small radius.
The R1 fiber units can be bent to r1mm, R2 to r2mm. Although, in general, bending a fiber unit shortens its detection distance, the distances of flexible fibers are not influenced by bending.
* To install a fiber unit on a moving part that repeatedly bends the fiber, bending-resistant fiber units are recommended.
Core A part of fiber that transfers light is a core.
The drawing below shows a diffuse fiber unit consists of an emitter core of φ0.5 and 9 receiver cores of φ0.25.
Retro reflective A fiber unit and reflector are installed on both sides to detect an object in between. Side-on and side-view A fiber unit that its detection direction is to a side of the unit with an optical system installed on the side.
With the Square units, it is called Side-On, and with the Sleeve units Side-View.
Aperture angle It is an angle of emitted and receiving light from a fiber unit.
Generally fiber units come with an aperture angle of 60˚, while narrow-view fiber units with 2~5˚.
Screen This comes with a lens to emit light in a flat beam.
This is suitable to detect objects with unstable reflection, due to not fixed passages or uneven shapes.
There is a similar type, Array. The Screen fiber units equipped with lenses come with narrower aperture angles for detection in long distances.
Narrow-view This is a fiber unit that comes with a built-in lens on its head unit for a narrow aperture angle of 2~5˚.
In addition to long-distance detection, as these do not get influence from light reflection from a reflective object beside the light axis, these are suitable for use of wafer mapping.
Sleeve A fiber unit has a thin tube, sleeve, on its head unit.
The Sleeve models are suitable to detect a small object in a narrow area.
There are fiber units with bendable sleeves and not-bendable sleeves available.
Bending resistance This is suitable to be installed on a moving part that repeatedly bend a fiber.
Their bending radius are r2 and r4 that are larger than those of Flexible fibers.
Free cut A fiber part can be cut by an included fiber cutter.
When a fiber unit is too long for an installation distance, an unnecessary part of the fiber can be cut off for easy installation.
Coaxial This is a kind of diffuse reflective fiber units that comes with multiple light-receiving cores installed around an emitter core, and is suitable to make detection in higher accuracy.
There are fiber units, which lenses for small object detection can be attached on.
Head-on and head-view These are fiber units that detects in a straight direction with optical systems on the top of fiber heads.
With the Square units, it is called Head-On, and with the thread and cylindrical units Head-View.
Through-beam Emitter and receiver units are installed on both side, facing each other, and detect an object in between.
This makes detection in a long distance possible.
Bending radius This is a smallest radius that a fiber unit can be bent.
Bending a fiber in a smaller radius may break fiber cores and result in a shorter detection distance or malfunction.
Thread A fiber head is structured with a screw nut for simple installation.
Water detection This is equipped with a LED with infrared light of 1.45μm wave length.
Special amplifiers, D3IF models, and fiber units, NF-TW01 and NF-DW01, for water detection are available. Detection of transparent liquid in a transparent glass bottle that was difficult with the conventional sensors can be made.
Diffuse reflective This is a fiber unit that comes with fibers of light emitter and receiver bundled in a single fiber and detect light reflection from an object.
While its detection distance is shorter, a single unit requires less installation work and space.
Lens A lens unit is attached on a fiber head.
These units are used for long-distance detection and space-saving with through-beam fiber units and small object detection with diffuse reflective units.
There are through-beam fiber units that come with built-in lenses.
Flat-on This has detection direction on its side with an optical systems on the large face on a head unit.
Thin dimensions to the detection direction of this type make it useful to be installed in a small space in its depth.
Liquid leakage detection This fiber head is installed on a leakage pan.
With capillary action, this can detect a small amount of liquid or viscous liquid.

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7. Control output

There are 2 polarities of transistor output, NPN and PNP.
A current flows from the Collector to Emitter on a NPN transistor.
On a PNP transistor, a current flows from the Emitter to Collector.

  • A load to NPN output can be connected to a power supply to the sensor or a separate power supply.

  • A power supply to load of PNP output must be the same with one to the sensor.
    Therefore, a separate power supply with a different voltage from one for the sensor cannot be used.

Voltage output of a transistor

With a NPN transistor, a voltage output flows through a pull-up resistor between a Collector and +V.
Unlike the open collector output, it does not require to connect an external resistor to have a voltage output.

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8. Connection

  • Generally , there are 3 types of connections for sensors, a cable, connector and terminal block, used.
    The standard cable length is 2 meters.
    For connector connection, M8 4-pin connectors are mainly used, as some sensors has M12 connectors and M12 pigtail cables.

  • M8 4-pin connector cables

    Straight L-shaped
    Cable length: 2m M84CN-2S M84CN-2L
    Cable length: 5m M84CN-5S M84CN-5L
    Cable length: 10m M84CN-10S M84CN-10L

    M12 connector cables

    Cable length:2m YF2A14-020VB3XLEAX
    (4 pin)
    (5 pin)

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