asg 6 data acquisition detection

130

6

chapitre

Acquisition de

données : détection

Présentation :

• Fonctions et des technologies de détection 6• Tableau de choix

chapter

Data acquisition:

detection

Presentation:

• Detection features and technologies

• Selection table

6 - Data acquisition: Summary

detection

6.1 Introduction 132

6.2 Electromechanical limit switches 133

6.3 Inductive proximity detectors 134

6.4 Capacitive proximity detectors 136

6.5 Photoelectric detectors 138

6.6 Ultrasonic detectors 140

6.7 RFID -Radio Frequency IDentification-detection 142

6.8 Vision 145

6.9 Optical encoders 149

6.10 Pressure switches and vacuum switches 154

6.11 Conclusion 157

6.12 Technology selection guide 158

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6 - Data acquisition: 6.1 Introduction

detection

The field of data capture is divided into two families.The first, called detection,

comprises products that can detect a threshold or limit or estimate a physical

measurement.The second – measurement or instrumentation – measures a physical

measurement to a given level of accuracy.

In this section, we shall only describe sensors and detection devices for machines

and their related automation systems.

Sensors designed for machine safety are dealt with in appropriate section.

For those who are interested, there are many works on machine safety describing

all the devices available on the market.

These products have three essential functions as shown in the figure 1.

The diversity of these functions requires manufacturers to produce a great number

of product variants to cover all the requirements. Recent innovations in product

modulation enable Schneider Electric to offer smaller ranges with more versatile

applications.

6.1 Introduction

b Detection: an essential function

The “detection” function is essential because it is the first link in the data

chain (C Fig. 2) of an industrial process.

In an automatic system, detectors ensure that data is captured:

- on all the events needed for operation that are used by the control

systems according to a preset program;

- on the progress of all the process phases when the program is running.

b Detection functions

There is a wide range of detection needs.

The basic ones are:

- controlling the presence, absence or position of an object,

- checking the movement, flow or obstruction of objects,

- counting.

These are usually dealt with by “discrete” devices, as in typical parts

detection applications in manufacturing chains or handling operations and

in the detection of persons or vehicles.

There are other more specific needs such as detection of:

- presence (or level) of a gas or fluid,

- shape,

- position (angular, linear, etc.),

- a label, with reading and writing of encoded data.

There are many additional requirements, especially with regard to the

environment, where, depending on their situation, detectors must be able

to resist:

- humidity or submersion (e.g.: higher water-tightness),

- corrosion (chemical industries or agricultural installations, etc.),

- wide temperature variations (e.g. tropical regions),

- soiling of any kind (in the open air or in the machines),

- and even vandalism, etc.

To meet all these requirements, manufacturers have developed all kinds of

detectors using different technologies.

b Detector technologies

Detector manufacturers use a range of physical measurements, the main

ones being:

- mechanical (pressure, force) for electromechanical limit switches,

- electromagnetic (field, force) for magnetic sensors, inductive proximity

detectors,

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A Fig. 1 Sensors functions

A Fig. 2 Data chain in an industrial process