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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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.

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Danger ! To understand the danger of radiation for human beings the following
two aspects have to be taken into account. There may be two different
types of danger.
•Intensity
If you focus for example the light of the sun in a burning glass, contact
with the skin can result in burns. If laser light is focussed (the human eye
also has a lens!) this can also lead to damage (see 2.3.2). The complete
quantity of energy per surface is decisive here. Other characteristics such
as the wave length are not important here.
•Wave length
This depends on the energy of the light particles. The shorter the wave
length, the higher the energy. For this reason ultraviolet radiation is
dangerous for us. Figure 11 shows that the sun emits most of the light in
the visible range. Nevertheless the share of the ultraviolet range is
enough to cause a sunburn.
Wave length and frequency Let us go into waves first. Waves are characterised by wave length and
frequency. In view of the correlation between the two quantities, it is
mostly enough to consider only one of these quantities. In the following
text only the wave length will be considered. The correlation is very
simple in a vacuum. In other media, such as glass, it can be more
complicated (dispersion). For applications with photoelectric sensors this
is however only important in rare cases. Since air has almost the same
effect on light as vacuum, this simple correlation can be used:
( 1) c = λ*f
c = 3 *109m/s: light velocity
λ[m]: wave length
f [1/s]: frequency
For visible light the typical wave length is for example:
500 *10-9 m (see 2.1.2).
The frequency results from ( 1):
0.6 *1016 Hz.
This is so high above the MegaHz (109Hz) and even the GigaHz range
(1012 Hz) that interference of photoelectric sensors by such waves of
comparably low frequency, such as by radio, can be excluded. The only
source of interference is extraneous light (see table "Influence of
interfering factors on different sensor types" in 3.1.2). The aspect that
these are electromagnetic waves need not be considered here. Strictly
speaking this applies to the area in front of the sensor. The electronics
can be influenced just like that of other types of sensors. The topic of
EMC is discussed in the training manual CE marking.
What does the wave look like? With regard to photoelectric sensors it is important that these waves are
transverse waves. This means that the oscillation (here of the electric and
magnetic fields) is vertical to the direction of propagation. A plane that is
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can be imagined as a straight line. The statement "vertical to the
direction of propagation" is thus ambiguous. There are two possibilities,
e.g. "upwards" or "to the side".
Polarisation Normally light has no preferred direction of oscillation. If the direction is
however limited to one single direction by a filter, this is called polarised
light. The plane defined by the direction of oscillation and the direction of
propagation is called polarisation plane (see 3.3.2, Figure 46 and Figure
47). Polarised light is especially used for one type of retro-reflective
sensor (see 3.3).
A classification into different ranges of wave length is called spectrum.
2.1.2 Ranges of wave length
Electromagnetic waves exist within a wide range. The only difference
between radio waves, visible light, X-rays etc. is their wave length.
Wave length Figure 2 shows the wave length that is called in most cases.
λ
Figure 2: wave length
The light which photocells require for the detection of an object consists
of wave lengths within the range of electromagnetic radiation between
approx. 1 mm and 10 nm. Within this range a distinction is made
between UV light (ultraviolet), light visible for the human eye and IR light
(infrared).

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cosmic rays
gamma rays
X rays mm waves frequencies of sound
long electr. waves
10
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l
[mm]
extreme extr. farfar farnear violet middlenearblue green yellow orange red
10
6
[nm]
l
4X10
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6X10 1,5X10
770622597577492455900020010
ultraviolet visible light infrared
radio waves
Figure 3: electromagnetic radiation spectrum
The upper part of Figure 3 shows the range that is of interest here. The
following table defines the range in more details.
Wave length range Radiation designation
100 nm - 280 nm
280 nm - 315 nm
315 nm - 380 nm
380 nm - 440 nm
440 nm - 495 nm
495 nm - 558 nm
558 nm - 640 nm
640 nm - 750 nm
750 nm - 1400 nm
1.4 µm - 3,0 µm
3.0 µm - 1000 µm
UV - C
UV - B
UV - A
light - violet
light - blue
light - green
light - yellow
light - red
IR - A
IR - B
IR -C
classification of the radiation spectrum to DIN 5031
The transitions between the individual ranges and the individual colours
of the visible light are continuous (cf. rainbow). The topic "colour" that is
important for one special sensor will be discussed in detail in 2.2.3.
λMost units use infrared light with the wave length λ= 880 nm as
transmitted light. But in some particular cases red light with a wave
length of λ= 660 nm and infrared light with λ= 950 nm are used. The
laser diode emits red light with a wave length of λ= 675 nm (cf. Figure
14). Moreover, there is a current trend towards red light, see below.
Infrared light The infrared light has several positive characteristics. It is among others
used to make units as resistant to external interference as possible.
•The receiver transistor in use (a diode for types OI and OP) has its
maximum sensitivity in the infrared range, see Figure 14.
•The transmitter diodes for infrared light have a higher efficiency that
is they emit more radiation when the same current is applied.
•This utilises the effect that light with a wave length longer than the
diameter of very small dust particles passes such particles almost

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without any problems at all (diffraction). This is why radiation at very
long wave lengths (IR and not UV) is used to provide protection
against soiling and dust, see Figure 4 and Figure 5.
•The units are less susceptible to extraneous light sources of the visible
range by the use of infrared light.
•The light spot is not visible which makes installation and adjustment
more difficult.
Diffraction The correlation between the size of the object, the wave length and the
term diffraction is explained briefly. We know from the so-called
geometrical optics that parallel light that strikes the object casts a
shadow, the edge of which is parallel to the direction of the light (Figure
4).
Figure 4: cast shadow
When the receiver is behind the object, no light can strike it. If the object
is smaller than the receiver, it is partly covered. If many small objects (dust
particles) are in front of the receiver, this can lead to the receiver
signalling "light beam interrupted". In this case this is a failure.
Malfunctioning due to soiling by dust is a typical problem for
photoelectric sensors (also see excess gain in 3.7).
If the object has almost the same size as the wave length (approx. 800
nm, see above), the phenomenon of diffraction can be observed. The
light can "go around the object".
light object shadow
Figure 5: diffraction
This means that the receiver can no longer be covered so easily.
light object shadow

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Most objects which are normally used are much bigger than the wave
length so that the principles of geometrical optics can be applied. But for
fine dust or mist a longer wave length is advantageous to reduce failures
caused by dust.
Is this diffuse? This must not be confused with a diffuse shadow we often see e.g. in
case of sunlight. This is due to the fact that it is no point source of light.
This is for example also the case for several light sources. In this context
this effect is however not important.
Red light In view of the advantages of the infrared light listed above this light is
used for most sensors. It must however be expected that the continuing
development and improvement of red light diodes will lead to an
increasing use of these diodes which are easier to install and adjust. In
addition there are other reasons to use red light. Summary:
•polarisation filters (see 3.3.2) for red light are better and less expensive.
•the attenuation in fibre optics (see 3.5) is smaller for red light.
•the light spot is visible, which makes installation and adjustment easier
2.1.3 Origin of light
Where do the small light waves come from?
The term "wave length" that characterises light was explained above.
Now the origin of light is to be explained. This topic is important to
understand the functioning of a laser. In this context the particle
character of the light is important.
Bohr atom First of all some fundamental principles will be mentioned. As we all
know matter consists of atoms or molecules. They consist of nuclei
surrounded by electrons. This is called electron sheath.
e
Figure 6: Bohr atom
In this atom model developed by the Danish physicist Nils Bohr the
electrons revolve around the atom nuclei like the planets revolve around
the sun (Figure 6).
Quantum It was a surprising discovery of modern physics that an atom or molecule
cannot emit any amount of energy but only defined "portions". These
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characterised by waves. Depending on the context light can also be
imagined as particles. The energy (e.g. by heating) can only be absorbed
in defined amounts. More precisely, the energy quantum is absorbed by
the electron sheath.
According to the Bohr atom model (Figure 6), the electrons cannot move
along random paths since the distance between the electron and the
nucleus depends on the energy. Only defined distances are "permitted".
These distances are only part of the model. In general we speak of energy
levels.
What does the material cause to emit light?
Excitation It must be excited to do so. If for example a suitable amount of energy is
supplied to an atom, an electron is "lifted" to a higher energy level. We
say that it is excited. In Figure 7 the vertical y-axis shows some of these
energy levels. No special atom is shown, the distances between the
energy levels were selected at random. In principle the figure is similar for
each atom or molecule. There is the lowest stable basic level. The gaps
between the energy levels become smaller the higher you get. Only an
exact amount of energy is important, that is the amount of energy should
exactly correspond to the distance between two possible energy levels.
Figure 7: excitation
There are different ways of excitation, not only by a light quantum as in
Figure 7. If a material, e.g. iron, is heated, it starts to glow. On atom level
this means that the atoms move faster and faster. They collide with more
and more energy until the energy exactly corresponds to the distance to
the next free energy level. In this case the electron is excited. In this
context the term "temperature" is important (see 2.2). The energy can
also be supplied in electrical form, e.g. for an LED, the filament of a light
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Emission This state is not stable. Sooner or later the electron "falls" down to its
basic level and emits its energy in form of radiation (Figure 8).
Figure 8: radiation
It cannot be foreseen when this will happen, sometimes sooner,
sometimes later. This is called spontaneous emission.
What is coherent? When several atoms are excited, they will not all emit radiation at the
same time. The light waves will not have the same rhythm. We say that
they are incoherent (Figure 9 and Figure 10).
Figure 9: coherent waves

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Figure 10: incoherent waves
What is the direction of the beam? The direction of the beam is not defined either. Normally light is radiated
evenly in all directions or is non-directional.
The radiation, the light quantum, has a defined energy and thus a
defined wave length. In the area of the visible light, its colour is also
defined (see 2.2.3).
2.1.4 Radiation spectrum
What does this light look like? For an LED a defined step between energy levels is preferred. This is why
the light is monochrome. Since the emission of the many electrons
involved is not simultaneous, the light waves do not have the same
rhythm, they are incoherent.
For other materials, such as the metal of a filament, many steps between
different energy levels are possible. This is why the light is not
monochrome here.
In some wave length ranges (in the visible range: colours) radiation is
higher, in others it is lower. A graph with the amount of energy on the y-
axis and the wave length on the x-axes shows the spectral distribution or
the spectrum of radiation. To enable a better comparison of the different
emitters, the curves are standardised, the maximum is always defined as
the value 1. Below please find some examples.

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200 300 400 500 600 700 800 900 1000 1100 1200 1300
0,5
1,0
1
l (nm)
Figure 11: spectrum of solar radiation
200 300 400 500 600 700 800 900 1000 1100 1200 1300
0,5
1,0
456
l (nm)
4: GaAsP
5: GaAlAsP
6: GaAs
Figure 12: Spectrum of LEDs
Figure 12 shows that the light of the LEDs is emitted in a very small wave
length range, it is almost monochrome. Curve 4 is in the red range of the
visible light, 5 and 6 are infrared.

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200 300 400 500 600 700 800 900 1000 1100 1200 1300
0,5
1,0
l (nm)
7
Figure 13: spectrum of the laser diode made of InGaAlP
The spectrum of the laser diode is almost a line at 675 nm. This light is
completely monochrome. This is explained below (2.3). The laser diode
used in the current units consists of InGaAlP.
For a better overview the spectres were shown separately. The following
Figure 14 shows all spectres.
2345678910111213
0,5
1
123
456
l (nm)
uv radiation visible light infrared radiationnear
1: sun light
2: sensitivity of the human eye
3: spectral sensitivity of the Si receiver
4, 5, 6: LED GaAsP, GaAlAsP, GaAs
7: laser diode made of InGaAlP
Figure 14: spectral curves
What are the consequences in practice? You can see that the sensitivity of the human eye is perfectly suited for
solar radiation. Curves 3 and 5 confirm the statement of 2.1.2 that the
sensitivity of the receiver is well suited for the LED with a wave length of