JUMO digital interfaces and bus systems for communication jun 2005 ISBN 3935742037 pdf

Digital Interfaces and Bus Systems for Communication Practical fundamentals Frank Blasinger Manfred Schleicher Preface Digital communication confronts us every day in modern process engineering: - it is used for configuring and setting the parameters for microprocessor instruments - serial bus systems, with minimum wiring requirements, are able to acquire a large amount of decentralized information and distribute it to the process equipment Intelligent field and automation devices can communicate directly with one another via a digital bus This book is intended as a step-by-step introduction to the subject of digital communications, for practical engineers and those new to this field The emphasis is on clarifying generalized topics, as well as including some JUMO-specific applications In this revised edition, the material on bus systems has been extensively updated The method of operation of bus systems for which JUMO has field devices available is explained in a practical manner Special thanks are due to all our colleagues, who helped us to prepare this book with their cooperation and professional input Fulda, March 2001 Manfred Schleicher English translation of the 3rd edition (revised) M.K JUCHHEIM GmbH & Co, Fulda Copying permitted with source reference! Part No 00392023 Book No FAS 603 Printed: 03.01 ISBN 3-935742-03-7 Frank Blasinger Contents Basic principles of digital interfaces and networks 1.1 Analog/digital signals 1.2 Data encoding 1.3 1.3.1 1.3.2 Types of data transmission 13 Operating modes of a transmission medium 17 Speed of data transmission 18 1.4 1.4.1 1.4.2 Media for data transmission 20 Transmission quality and cable terminating resistance 22 Modem 23 1.5 Properties of various interfaces 25 1.6 1.6.1 1.6.2 1.6.3 1.6.4 1.6.5 Networks and bus operation in automation Communication networks and levels Fieldbus topologies Centralized and distributed arrangement of automation devices Access methods Bus communication 1.7 OSI reference model 57 1.8 1.8.1 1.8.2 1.8.3 1.8.4 Network management Functions of MAC and MAP The data structure Error checking Connection of networks via repeater, bridge, router and gateway 61 61 64 66 68 1.9 1.9.1 1.9.2 1.9.3 Operation through application programs Configuration software (setup program) Project design software Measurement display and operation using visualization/evaluation software 72 73 75 76 Important fieldbus systems 81 2.1 HART communication 83 2.2 ASI bus 85 2.3 Bitbus 86 2.4 CAN bus 88 2.5 FIP bus 93 2.6 Interbus 94 2.7 LON bus 96 2.8 Modbus 97 2.9 P-Net 98 2.10 PROFIBUS 100 2.11 FOUNDATION fieldbus 105 2.12 Ethernet 107 38 40 44 48 49 54 Contents 2.13 Summary of the fieldbus systems 111 Organization of the data system for JUMO 113 3.1 3.1.1 3.1.2 The various communications options 114 Physical interfaces 114 Transmission protocols and fieldbus systems 114 3.2 JUMO instruments with HART 116 3.3 JUMO instruments with CANopen 118 3.4 3.4.1 3.4.2 3.4.3 3.4.4 JUMO instruments with LON The JUMO mTRON concept Network structure Hardware architecture of a LON device Communication procedure 120 120 122 123 124 3.5 3.5.1 3.5.2 3.5.3 3.5.4 3.5.5 JUMO instruments with Modbus/Jbus Physical interface and data flow Master/slave principle Transmission mode Format of the data blocks Connection via an interface converter 126 126 127 128 129 130 3.6 JUMO instruments with PROFIBUS 132 3.7 Checklist for fault-finding in serial interfaces 134 Outlook 137 4.1 4.1.1 4.1.2 4.1.3 Standards and technologies in automation engineering NOAH (Network Oriented Application Harmonization) OPC (OLE for Process Control) for communication Ethernet fieldbus equals system bus 4.2 Long-distance data transmission 143 4.3 Distributed systems 145 137 137 138 141 Index 147 Basic principles of digital interfaces and networks This chapter deals first of all with some basic principles The aim here is to achieve this without over-complex theoretical or mathematical treatment Amongst other things, the basic facts about data encoding, types of data transmission, properties of different interfaces, construction of networks etc are explained for practical engineers, who are increasingly faced with the subjects of digital communication and bus systems in modern automation engineering 1.1 Analog/digital signals In today’s automation engineering, more and more devices operate digitaIly This is in contrast with the more familiar analog measurement technology and data transmission This means that digital process instruments are increasingly replacing analog type instruments in modern process control, part because of the technological advances and the advantages offered Nowadays, digital transmission is even superseding the use of familiar standard signals such as — 20mA, — 10V, etc for the transfer of analog measurements The main features of different data transmission technologies are explained in more detail below Analog signals A measurement, a temperature for example, is converted into a signal corresponding to this temperature by a measuring device The signal could be, for instance, a — 20mA current Every temperature value corresponds clearly to a value of electrical current If the temperature changes continuously, the analog signal also changes continuously In other words, a characteristic feature of analog transmission is that the amplitude of the selected signal varies continuously over time (see Fig 1) Fig 1: JUMO, FAS 603, Edition 07.02 Analog signal with continuously changing amplitude Basic principles of digital interfaces and networks In automation engineering, such standard signals (4 — 20mA) are transmitted in pure analog form as a normalized current signal A temperature value is measured by a Pt100 resistance thermometer, then converted into a current proportional to the measurement by a transmitter, and subsequently transmitted to a controller, indicator and recorder (see Fig 2) By means of the current, every change in measurement value is immediately recorded by each instrument connected in the circuit Fig 2: Analog signal transmission In measurement engineering, the information content of an analog signal is very limited in comparison with acoustic (sound) or optical (light) data transmission Apart from the advantages of an unambiguous, continuously reproduced measurement, with simultaneous supply of power to the measurement recorder (e.g two-wire transmitter), the information content of the analog signal consists only of the magnitude of the measurement, and whether or not the signal is available at the connected device Digital signals The term “digital” is derived from the word “digit” and comes originally from the Latin “digitus = finger” Digital means sudden or step changes, i.e a digital signal does not vary continuously In the example of temperature measurement, this means that the analog measurement is divided into specific value bands, within which no intermediate values are possible The values are read at fixed time intervals, the sampling time The task of conversion is carried out by an analog to digital converter (or ADC) Here, the accuracy or resolution of the signal depends on the number of value bands and the sampling frequency In the example shown in Fig 3, samples are taken every 20msec, with a subdivision into 10 value bands JUMO, FAS 603, Edition 07.02 ... Digital Interfaces and Bus Systems for Communication Practical fundamentals Frank Blasinger Manfred Schleicher Preface Digital communication confronts us every... The various communications options 114 Physical interfaces 114 Transmission protocols and fieldbus systems 114 3.2 JUMO instruments with HART 116 3.3 JUMO instruments... properties of different interfaces, construction of networks etc are explained for practical engineers, who are increasingly faced with the subjects of digital communication and bus systems in modern