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Lead Contents

Photomicro Sensors

These Optical Sensors provide a compact, low-cost method to detect workpieces. Many models are available, including Slot-type Sensors (through-beam) for non-modulated or modulated light, Reflective Sensors, and Sensors with separate emitters and receivers.

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Primary Contents

Operating Principles

(1) Properties of Light

Rectilinear Propagation

When light travels through air or water, it always travels in a straight line. The slit on the outside of a Through-beam Sensor that is used to detect small objects is an example of how this principle is applied to practical use.


Refraction is the phenomenon of light being deflected as it passes obliquely through the boundary between two media with different refractive indices.

Reflection (Regular Reflection, Retroreflection, and Diffuse Reflection)

A flat surface, such as glass or a mirror, reflects light at an angle equal to the incident angle of the light. This kind of reflection is called regular reflection. Retroreflectors (also called a corner cube) take advantage of this principle by arranging three flat surfaces perpendicular to each ther. "Retro" means "to return toward the source." The light reflected off the reflectors travels back towards the emitter, thus the term retroreflective".
Matte surfaces, such as white paper, reflect light in all directions. This scattering of light is called diffuse reflection. This principle is the sensing method used by Diffuse-reflective Sensors.

(2) Light Sources

Light Generation

<Non-modulated Light>

Non-modulated light facilitates high-speed response by continuously radiating a constant amount of light. There is the drawback, however, of susceptibility to external light interference.

<Modulated Light>

Modulated light is not affected by sunlight, light from incandescent bulbs, and other external light interference. An LED emitter is pulselighted, and the received signal is processed to remove the DC component.