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Classification methods & Classification - Photoelectric Sensors

Introduction &
Features

Classification
methods &
Classification

Precautions for
prorer use

Principles of
particular optical
sensing systems

Functions

Classification methods & Classification

Classification methods

There are various types of photoelectric sensors. Four different methods of classification, depending on the objective considered, are explained here.

(1) Classification by structure

This classification is based on the manner in which the circuit configuration elements are built-in or separated. This classification is useful to select sensors in view of the mounting space, power supply and noise immunity.

Refer to Classification by structure

Photoelectric sensor	Amplifier built-in
	Power supply built-in
	Amplifier-separated
	Fiber type

(2) Classification by sensing mode

This classification is based on how the light is emitted and received and on the sensor shape. This classification is useful to select sensors in view of the sensing object size and the surrounding conditions.

Refer to Classification by sensing mode

Photoelectric sensor	Thru-beam type	General purpose
		U-shaped
		Area
	Retroreflective type	General purpose
		With polarizing filters
		Transparent object detection
	Reflective type	Diffuse reflective
		Narrow-view reflective
		Convergent reflective
		Adjustable range
		Mark sensing

(3) Classification by beam source

This classification is based on the type of beam source used.
This classification is useful to select sensors in view of the sensing distance and the color differences of objects. LED is used on the emitting element. However, we also have the laser sensor uses semi-conductor laser.

Refer to Classification by beam source

Photoelectric sensor	Infrared beam
	Red beam
	Green beam
	Blue beam
	Three color beam (Red, Green, Blue)

(4) Classification by output circuit

This classification is based on the type of output circuit and the output voltage.
This classification is useful to select sensors according to the input conditions of the device or equipment connected to the sensor output.

Refer to Classification by output circuit

Photoelectric sensor	ON / OFF output	NPN open-collector transistor
		PNP open-collector transistor
		DC 2-wire
		NPN transistor universal
		Relay contact
	Analog output	Analog voltage

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Classification

(1) Classification by structure

Type	Outline and Features
Amplifier built-in		Since the amplifier is built-in, just connecting the DC electric power supply can provide a Non-contact output.
Power supply built-in		Since all necessary functions of a photoelectric sensor are incorporated, just connecting the electric power supply (100 V / 200 V AC) can provide a relay contact output.
Amplifier-separated		As the sensor head contains only the emitting and the receiving elements, its size can be made small. Further, the sensitivity adjustment can be done from a remote place.
Fiber		It has supreme environmental resistance, since the sensing portion (fiber) contains absolutely no electrical parts.

Feature comparison table

Feature	Sensor head size	Noise immunity	Lifetime	Ease of use
Amplifier built-in	○	○	◎	○
Power supply built-in	△	○	△	◎
Amplifier-separated	◎	△	◎	○
Fiber	◎	◎	◎	◎

◎	:	Excellent
○	:	Good
△	:	Fair

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(2) Classification by sensing mode

Thru-beam

Type	Outline and Features
General purpose	Detects an object that interrupts the light beam traveling from the emitter to the receiver. Long sensing range Precise detection Small object detectable Not affected by shape, color or material of sensing objects (opaque) Resistant to dirt and dust on the lens
U-shaped	The emitter and the receiver are in one enclosure. No beam alignment needed Precise detection Small object detectable Not affected by shape, color or material of sensing objects (opaque) Resistant to dirt and dust on the lens
Area	Light curtain or area sensor is made up of arrayed emitting and receiving elements. Object is detectable as long as it is anywhere in the defined sensing area Not affected by shape, color or material of sensing objects (opaque) Resistant to dirt and dust on the lenses Thin objects, such as postcards, can be detected (Cross-beam scanning type only. Refer to "Principles of particular optical sensing systems")

Retroreflective

Type	Outline and Features
General purpose	Detects an object that has a reflectivity smaller than the reflector and interrupts the light beam traveling between the sensor and the reflector. Easy beam alignment Wiring only on one side Space saving compared to thru-beam type sensors Not affected by shape, color or material of sensing objects (opaque)
With polarizing filters	It enables detection of even a specular object by attachment of polarizing filters to the emitting and the receiving parts. (Refer to "Principles of particular optical sensing systems") Specular object detection Easy beam alignment Wiring only on one side Space saving compared to thru-beam type sensors Not affected by shape, color or material of sensing objects (opaque)
Transparent object detection	The specially devised optical system enables detection of even a transparent object. Transparent object detection Easy beam alignment Wiring only on one side Space saving compared to thru-beam type sensors Not affected by shape, color or material of sensing objects

Reflective

Type	Outline and Features
Diffuse reflective	Emits a beam onto the object and detects the object by receiving the beam reflected from the object surface. No beam alignment needed Space saving Wiring only on one side Object with fluctuating position detectable Wide sensing area
Convergent reflective	Detects an object in the area where the emitting and the receiving envelopes overlap. A spot-beam type sensor detects an object at just the point where these envelopes cross over. Less affected by background and surroundings Precise detection No beam alignment needed Space saving Wiring only on one side
Adjustable range reflective	Detects an object in the area where the emitting and the receiving envelopes overlap. A spot-beam type sensor detects an object at just the point where these envelopes cross over. Less affected by background and surroundings Precise detection No beam alignment needed Space saving Wiring only on one side
Adjustable range reflective	Emits a spot beam onto an object and senses the difference in the reflected beam angle. (Refer to "Principles of particular optical sensing systems") Virtually not affected by shape, color or material of sensing objects. Hardly affected by background and surroundings Small object detectable with high accuracy No beam alignment needed Space saving Wiring only on one side
Mark sensing	Projects a spot-beam on the target color, and identifies the color by sensing the amount of reflected beam and the relative ratio among color components. [FZ-10 series and LX-100 series (when the color mode is set)] Or projects a spot-beam on an object, and identifies the color by the proportion of the amount of light received (contrast), not by the difference in the amount of the reflected beam. [LX-100 series (when the mark mode is set)] Color identifiable Hardly affected by background and surroundings Small object detectable with high accuracy No beam alignment needed Space saving (FZ-10 series) Wiring only on one side

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(3) Classification by beam source

Type	Features
Infrared beam	Intense beam offers long sensing range Unable to expose films
Red beam	Suitable for color mark sensing Visible We also have laser sensors that used semiconductor lasers instead of LEDs.
Green beam	Suitable for color mark sensing Suitable for minute detection because of a high beam damping ratio. Visible
Blue beam	Suitable for color mark sensing Suitable for minute detection because of a high beam damping ratio. Visible
Three color beam (Red, Green, Blue)	Color detected by resolving it into three color components Fine color discrimination possible

Color combinations that can be discerned during mark sensing

Mark color	White	Yellow	Orange	Red	Green	Blue	Black
Background color	White	Yellow	Orange	Red	Green	Blue	Black
White	-	(B)	(B)	(G)(B)	(R)(G)(B)	(R)(G)(B)	(R)(G)(B)
Yellow	(B)	-	(G)	(G)	(R)(G)(B)	(R)(G)(B)	(R)(G)(B)
Orange	(B)	(G)	-	(G)(B)	(R)(G)(B)	(R)(G)(B)	(R)(G)(B)
Red	(G)(B)	(G)	(G)(B)	-	(R)	(R)(B)	(R)(B)
Green	(R)(G)(B)	(R)(G)(B)	(R)(G)(B)	(R)	-	(B)	(B)
Blue	(R)(G)(B)	(R)(G)(B)	(R)(G)(B)	(R)(B)	(B)	-	(B)
Black	(R)(G)(B)	(R)(G)(B)	(R)(G)(B)	(R)(B)	(B)	(B)	-

(R)	:	Red LED type
(G)	:	Green LED type
(B)	:	Blue LED type

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(4) Classification by output circuit

ON / OFF output

Type

Outline and Features

NPN open-collector transistor

Able to drive a relay, PLC, TTL, logic circuit, etc.
A separate power supply can be used for the load.
Long life
High-speed response
Commonly used in North America or Japan

Symbols

D	:	Reverse supply polarity protection diode
ZD	:	Surge absorption zener diode (Its position differs with the model.)
Tr	:	NPN output transistor

PNP open-collector transistor

Commonly used output circuit in Europe
Power supply is not required for the load.
Long life
High-speed response

Symbols

D	:	Reverse supply polarity protection diode (Its position differs with model.)
ZD	:	Surge absorption zener diode (Its position differs with the model.)
Tr	:	PNP output transistor

DC 2-wire

Wire saving
Low current consumption
Long life
High-speed response
Limitation on connectable load

Symbols

ZD	:	Surge absorption zener diode
Tr	:	PNP output transistor

NPN transistor universal

Able to drive a relay, PLC and logic circuit
Long life
A separate power supply can be used for the load.
(However, its voltage must be higher than the sensor power supply.)
High-speed response

Symbols

D1	:	Reverse supply polarity protection diode (Its position differs with the model.)
D2	:	Reverse current prevention diode (Its position differs with the model.)
ZD	:	Surge absorption zener diode
Tr	:	NPN output transistor