IFM Electronic Efector 200 Guida all'installazione

Photoelectric sensors

Training manual

ifm electronic

Sensors, networking

and control technology for

automation

Training manual

Photoelectric sensors

Training manual

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

Photoelectric sensors

Training manual

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

Photoelectric sensors

Training manual

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

Photoelectric sensors

Training manual

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

Photoelectric sensors

Training manual

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.

Photoelectric sensors

Training manual

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.

Photoelectric sensors

Training manual

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.

Photoelectric sensors

Training manual

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.

Photoelectric sensors

Training manual

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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