IFM Electronic Efector 200 Installation guide

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Photoelectric sensors
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ifm electronic
Sensors, networking
and control technology for
automation
Training manual
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Photoelectric sensors

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Photoelectric sensors
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Training manual photoelectric sensors (as in March 2003)
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Note on guarantee
Utmost care was taken when writing this manual. Nevertheless, we cannot guarantee that the contents are correct.
Since it is impossible to avoid mistakes despite intensive efforts, we always appreciate indications.
We reserve the right to make technical alterations concerning the products so that deviations from the contents of the
training manual may result.
For further information, data sheets, prices, etc. please go to www.ifm-electronic.com

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Contents
1 Introduction 6
1.1 Photoelectric sensors in industrial applications 6
1.2 Notation 8
1.3 On the contents 8
2 Light 10
2.1 Electromagnetic waves 10
2.1.1 Nature of the light 10
2.1.2 Ranges of wave length 12
2.1.3 Origin of light 15
2.1.4 Radiation spectrum 18
2.2 Radiation and temperature 21
2.2.1 Black emitters 21
2.2.2 Emission 21
2.2.3 Reflection and colour 22
2.3 Laser 24
2.3.1 Meaning 24
2.3.2 Features 25
2.3.3 Terms 27
2.3.4 Laser sensors 28
2.4 Refraction 29
3 Characteristics of photoelectric sensors 32
3.1 Comparison with other types of sensors 32
3.1.1 Definition 32
3.1.2 Immunity to interference of different sensor types 33
3.1.3 Ranges of sensor systems 33
3.2 Through-beam sensors 34
3.2.1 Operating principle 34
3.2.2 Information on the use of through-beam sensors in practice 38
3.3 The retro-reflective sensor 43
3.3.1 Operating principle 43
3.3.2 Use of retro-reflective sensors in practice 48
3.3.2.1 Sensors with polarisation filter 48
3.3.2.2 Laser units and prismatic reflectors 50

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3.3.2.3 Prismatic reflector 51
3.3.2.4 Summary 53
3.4 Diffuse reflection sensors 54
3.4.1 Operating principle 54
3.4.2 Notes on the use of diffuse reflection sensors in practice 56
3.4.2.1 Range 56
3.4.2.2 Setting 58
3.4.2.3 Background suppression 60
3.4.2.4 Summary 64
3.4.3 Units with special features 65
3.5 Fibre optics 67
3.5.1 Typical applications 67
3.5.2 Operating principle 68
3.5.3 Notes on the use of fibre optics in practice 71
3.6 Light-on and dark-on mode 73
3.7 Excess gain 76
3.7.1 Meaning 76
3.7.2 Setting 78
3.8 Switching frequency 80
4 Examples of photoelectric sensors 83
4.1 Technology 83
4.1.1 Circuitry 83
4.1.2 Operational reliability and failure warning 85
4.2 Current and voltage ranges 91
4.2.1 Leakage current, minimum load current and voltage drop 92
4.2.2 Connection 92
4.3 Handling 97
4.3.1 Setting of the sensing range 97
4.3.1.1 OG as through-beam sensor 98
4.3.1.2 OG as retro-reflective sensor 98
4.3.1.3 OG as diffuse reflection sensor 100
4.3.1.4 OGH as diffuse reflection sensor with background suppression 102
4.3.1.5 Displays and other settings 102
4.3.2 Timers 106
4.4 Mechanical properties 112
4.4.1 Designs and ranges 112
4.4.2 Mounting 112
4.4.3 Lens attachment 122
4.5 Overview 122

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4.6 Units with special properties 125
4.6.1 Side or front lens 125
4.6.2 Separate amplifier 125
4.6.3 Contrast sensor 127
4.6.4 Colour sensor 128
5 Infrared sensors 131
5.1 Operating principle 131
5.1.1 Radiation 131
5.1.2 Degree of emission 132
5.1.3 Technology 133
5.2 Information on practical use 135
5.2.1 Angle of aperture 135
5.2.2 Setting instructions for OWI 139
5.2.3 Operating conditions 140
6 Applications 143
6.1 Photoelectric sensors 143
6.1.1 Recommended sensor types 143
6.1.2 Application examples 144
6.2 Infrared sensors 150
Annex 159
Type keys 159
Production code 163
Table degree of emission 164
Table range on prismatic reflectors 166
Glossary of technical terms 170
Index 174

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1Introduction
1.1 Photoelectric sensors in industrial applications
What are they used for? Photoelectric sensors have become indispensable components in almost
all automated production processes.
Photoelectric sensors are used for safe and fast detection, positioning and
counting of parts.
We would like to start with one example of the variety of applications.
Other applications can be found below (see e.g. 6.1.2).
Figure 1: edge and sag monitoring
What is monitored here? The example shows the variety of applications. The sensors monitor
whether the material is transported in a straight line and whether the size
of the sag is sufficient. This sag functions as a buffer so that the material
does not tear if the process is disturbed or in case of a sudden stop. This
application exists in many industries:
•paper production
•paper processing (printing house, packing industry)
•plastic processing (production of carrier bags)
•textile industry etc.
Photoelectric sensors have the largest market share of the binary position
sensors. As a tendency the market will increase. Market increases of
approx. 8 to 9% a year are forecasted.

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Examples
Type Accessories Market segment
OF --- packing industry
OBF fibre optics packing industry and automation
OG angle brackets packing industry; food industry
OL angle brackets with
protective cover
materials handling
OJ mounting components food industry
Modern photoelectric sensors offer a precise lens and intelligent
electronics as a standard. Both components are integrated in robust
housings made of resistant plastic or metal. The technical problems of
earlier sensor generations such as interference by extraneous light or
short cleaning and maintenance intervals have almost been solved today.
Three fundamental physical principles with several subgroups provide a
solution to many different problems in different applications. The correct
selection of the fundamental principle and of the type is very important
for safe functioning. The sensing range is one main criterion for the
selection of the correct sensor (see 3.1).
The present and the future
Easy handling and reliability There is a current trend towards more intelligence in the sensor (e. g. see
3.4.2). In future there will hardly be a photoelectric sensor without
microprocessor. This will lead to easier use, especially setting, as well as
increased operational reliability.
Mechanics Another trend that also applies to other sensor types is that useful
accessories can increase the user's benefit. In this case angle brackets
that protect the sensor against mechanical damage in rugged
applications and mounting accessories that make alignment and
adjustment easier are offered. This becomes more and more important
since the sensors are increasingly compact by the use of microprocessors
and the development of other components. Sensors with comparable or
improved characteristics have only a fraction of the volume of the units
developed in the past.
Special applications Robust angle brackets enable the use of sensors such as OL in conveyor
systems. Other sensors have special optical features for special
applications, e.g. colour sensors, contrast sensors or laser units. For a
better understanding of the functioning and the characteristics, the
chapter about the fundamental principles of optical sensing was
extended considerably.

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1.2 Notation
The notation is explained here to make it easier to read the text and to
find information.
Headwords Headwords are indicated at the left margin. They give information on the
topic in the following paragraph.
What does FAQ mean? It means Frequently Asked Questions. This term is often used for modern
electronic media. Almost every beginner of a new topic has the same
questions. Sometimes they can be found at the beginning of a paragraph
instead of a headword. They are written in italics to distinguish them
from simple headwords.
( 4) A number in round brackets at the left margin indicates a formula that is
referred to later in the text, e.g. see ( 4). Of course these formulas need
not be learned by heart. They are to facilitate the understanding of the
matter because like a figure a formula describes the context in a shorter
and clearer way than many words.
1.3 On the contents
This manual describes the principles of the photoelectric sensors.
Important terms and correlations are explained, state-of-the-art
technology is described and technical data of the units are given. This
results in the following structure.
1. Introduction This introduction is followed by the chapter:
2. Light This chapter contains a short description of the physical principles which
are useful for a better understanding of the functioning and the
characteristics especially of laser and infrared units. Some basic terms and
their correlation are described.
3. Characteristics of the photoelectric sensors
Characteristics of binary sensors are discussed. Other more complex
systems that are also used in practice are mentioned. A general overview
of the different sensor systems follows. Among others, this is to facilitate
a correct classification of photoelectric sensors as well as the decision
where they can be used and where not. Afterwards the three sensor
versions and their specific features are presented. The knowledge of
these features, the advantages and disadvantages, is a prerequisite for a
useful discussion with users.
4. Examples of units In this chapter the data of sensors are given and explained. The
mechanical structure, the optical and electrical characteristics, the use
and the setting of the range are described here. In addition some
applications are presented.

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Annex This manual is also meant for your own studies. Terms that are less
frequently used are explained in a short technical glossary. The points
that are essential for the photoelectric sensor are explained in details in
the preceding chapters. The index helps to look up a topic. The glossary
contains another short explanation of important terms. The type key and
the code for the production date are also presented briefly.
Much success! On the basis of this manual everyone should be able to make use of the
opportunity provided by photoelectric sensors and successfully implement
them.

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2Light
Is it necessary to know this? In this chapter the physical principles are described briefly. If you know
this or remember what you have once learnt about it, the understanding
of the operating principle and the overview of the sensor types and their
use is easier. Knowledge of the principles is important especially to
understand how a laser unit works. Of course, you can also use such a
unit without knowing what a laser is. But basic knowledge is necessary to
be a competent partner in discussions. The following information allows
a better understanding of the special features of the infrared sensors.
This presentation shall however not be too extensive or theoretical. We
try to concentrate on essential information. This requires shortening and
simplification.
2.1 Electromagnetic waves
2.1.1 Nature of the light
What is light? For a long time experts argued about the question what light really is.
Some people, such as Newton, were of the opinion that light consists of
small particles, the photons. This is how today we image electrons for
example.
Wave? The other opinion was that light is a wave that has characteristics similar
to a water wave. Many experiments the results of which can only be
explained by interference have strengthened this opinion. Interference
results from a superposition of waves (see Figure 2). If the crest of a wave
meets the hollow of a wave, the light intensity is 0. If however a crest
meets a crest or a hollow meets a hollow, the wave is intensified. (please
also see the term "granular" in 2.3.2).
Duality Modern physics, quantum physics, among others based on Einstein's
ideas, found a solution worthy of a Solomon at the beginning of the 20th
century. The question: "wave or particle?" is answered by: "it depends"
or "both". This concept that is called duality cannot be explained in more
detail here. It is only mentioned to explain that it is no contradiction to
use the one or the other aspect as an explanation of a phenomenon.
Interpretation A short comment on this: physics is a so-called "exact" science. This is
often interpreted as a rigid system of everlasting truths expressed by
formulas that are difficult to understand. This has a deterrent effect on
many people. It is not considered that in physics there are also heated
discussions about "interpretations" that we normally know from
theology. This shows that it can also be exciting to deal with such
principles.