SENSORS AND ACTUATORS NETWORKS

The sensors and actuators networks are low level networks well adapted to the automation of workshops, of production lines or of machines. The main purposes of these networks are to reduce the cost of the connections, to make easier the installation, the adjustments, the operations and the maintenance of the industrial automation devices linked to the network. Some network interfaces specify the network infrastructure, the hardware protocols and the software protocols all together while some other interfaces - such as IO-Link - specify only the exchanges of data. Many of these systems encapsulate their own protocol into other ones too, allowing them to adopt various topologies and media.

The « AS-I bus » is a low cost sensors and actuators network based on a master / slave architecture and supports the most current topologies.

• Its first specificity is that it needs only one line ( two wires ) to transport both the 24 VDC electrical power and the data.
• Its second specificity is simply resumed by using the « snap and go » modules, in order to add a new slave device quickly and easily.

The data are transmitted through hardware methods, firstly by encoding them ( Manchester encoding ), secondly by modulating the power line with alternate pulse for data transfer ( ATM technology ). The time critical data ( the inputs and the outputs of the slaves ) are transmitted by cyclic polling, when the other types of data ( such as configuration parameters ) are transmitted asynchronously.

This communication system can provide safety features when necessary.

The « AS-Interface » association provides a whole of technical information by e-learning in its virtual academy.

• You will find there all the fundamental knowledge to get about the technology : the full description of the system, the description of many devices plus the presentation of the master-slaves nodes.
• You will also read there a list of many problems which can occur while designing or installing a network, with practical examples illustrating how to implement them correctly.
• The AS-interface association offers a knowledge data base including the most frequently asked questions ( FAQ ), installing advices as well as applications examples.

www.as-interface.net

« DeviceNet » is an industrial communication system part of the CIP network system family. It has been designed to operate communications at the lowest level of an automated plant, in order to exchange data between programmable controllers and field devices.

The system is technically based on CAN bus concerning the physical layers and on the CIP protocol concerning the upper layers. Actually, its protocol is an adaptation of the CIP protocol to the CAN standard, which its designer have added some useful additional features to, such as hot plugging, diagnostic capabilities, redundancy capabilities and more.

This communication process uses both the producer-consumer model and the client-server model in order to manage the data flow between the different installed devices. It exchanges the data from point to point, choosing either a master-slave architecture or a distributed architecture, according to the desired configuration.

• Introduction To Devicenet.

  This page, well illustrated with a video, introduces to this digital communication network, and shows what are the relationships between the network system, the CAN bus standard and the CIP protocol.

  • It explains the CIP objects used to operate the communication, especially what are the application objects and the vendor specific objects.
  • It describes how messages are managed according different point of view ( master-slave model, distributed model, I/O connections and more ).
  • Finally, you will read considerations related to addressing, error states, master devices ( network scanner ), slave devices, physical media, EDS ( Electronic Data Sheet ) and more, before a presentation of some typical Devicenet devices.

  www.rtaautomation.com

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• DeviceNet tutorial. ( )

  This very comprehensive 41 pages document describes the open architecture in use, the basics of both DeviceNet and CAN bus, plus details on the physical media. Then it teaches you how to build a system and what are its main characteristics.

  Richard Burch

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• DeviceNet Technical Overview. ( )

  This document is the image of the page above from « rtaautomation », with a few differences. Particularly, it details how the OSI layers are implemented in the communication system.

  www.rtaautomation.com

This guide focuses on the media and how to design and to install such a communication system. You will learn here how to set up a network, what are the available topologies and what are the different available media. Then, you will read a description about the cable system and its components, the connections, how to compute the power requirements, how to diagnose network problems and how to prevent them.

www.odva.org

« Interbus » is a sensors and actuators deterministic bus originally designed by the Phoenix contact company. Nowadays, the whole of this technology is embedded into the Profinet IO network system provided by the Siemens company ( Profinet IO is compliant with the previous versions of « Interbus », by using a dedicated proxy as a gateway ). « Interbus-Safety » is a specific version of « Interbus », which is dedicated to safety networking applications.

Main specificities.

• Addresses depend on the physical location of the devices in the network.
• IO data transfer optimization is operated by using a single frame for all the devices.

  This frame is generated once the network configuration has been, validated.

• Possibility to hot-plug the devices in and out, with the objective to make the maintenance operations easier.

Since its hardware specifications suggest using a single-line-only through all the devices with the objective to send the requests and the answers together, the network topology has evolved towards a ring topology with branches looking like a tree topology.

According to the communication process, the protocol is based on a single-master / slaves model, and exchanges the data through two channels : one for the process data ( the inputs and the outputs ) and the other for the services data ( configuration, diagnostic and more ). In its late versions, « Interbus » integrates the TCP/IP protocol in a separated channel.

To operate the configuration, the monitoring and the diagnostic of Interbus, it is enough to use the CMD software which is a single tool available for all the control systems.

The « Interbus » association provides some documentation about its networking technologies that you can download freely.

• Concepts and basics about Interbus sensors and actuators network.

  Introduction to the network, knowledge base, data transmission, industrial automation, maintenance, control, standardization.

• Technical guides such as data transmission cable features and optical fibre features.
• Interfaces to exchange data with other industrial data protocols and automated systems.

   ( Drivecom profiles, incremental coders, process controllers, robots controllers, M12 plugs specifications, optical fibre plug specifications and a little more. )

www.interbus.de

• Interbus basics. ( )

  This document presents the main characteristics and features of this sensor/actuator network. Particularly, it shows a good overview of the data transmission process and a good overview of the maintenance features.

  www.interbus.de

This system is a communication interface intended for the lowest field devices such as sensors, actuators or instruments.

Here you will discover that strictly speaking, this communication system does not consist in a network, but it rather consists in a data exchange interface extension for field bus systems, increasing their potential.

This data transmission technique has the objective to make a device stock uniform, proposing supplementary appropriate and useful functions in the same time ( diagnostic, adjustment ) for installation, maintenance and operation.

The bus specifications have evolved with the Ethernet TCP/IP integration. By the time now, the transmission process encapsulates the original messages ( RS485 ) into the Ethernet frames, resulting in a well adapted distributed network serving automated industrial plants.

• Basic concepts.

  General introduction, definitions, usages.

• Main characteristics.

  List of some of them about cabling, memory, error management, performances, compatibility with other systems etc.

• Architecture.

  Introduction to the basic components, to the master module, to the direct connections and to the distributed architecture.

• Data exchange process.

  Introducing the protocols, the switched mode, the serial communication mode, plus the process, service and event data.

• Operating the devices.

  Presentation of the configuration files.

• Resources.

  Links to technical specifications and to some other technical papers.

www.bh-automation.com

« P-Net » is a process fieldbus, registered as an international standard under IEC 61158 reference. This process dedicated communication bus has been designed by the « Proces Data » company in Denmark which continue to maintain it.

This industrial digital communication system has been expressively designed to exchange data with sensors, actuators and measurement devices and to provide device configuration as well as device diagnostic services.

The multi-master / slaves model is used to process the communication, using the token communication technique to manage the master accesses ( implemented as a virtual token ).

This network supports multiple topologies ( ring, tree, star ), with some other capabilities like segmentation ( multi networks technique ), hot plugging, redundancy, while being rather media independent. One of its specificities consists in the possibility to modify the address of any device while the bus is operating.

By the time being, P-Net supports Ethernet TCP/IP, since it embeds the early RS 485 messages in the Ethernet frames, leading in a full factory automation distributed network system.

The International « P-NET User Organization » ( IPUO ) promotes this standard and provides some technical informations.

• P-Net technology basics ( available in .pdf file format in english, in german and in russian ).

  This folder presents the technical principles of this digital network, its history, its architecture, and develops some specific characteristics such as the « virtual token passing ».

www.p-net.dk / www.proces-data.com

Here, the « Proces Data » company - the designer of the « P-Net » digital communication system - presents the technology developed by its team and how to use it as its best.

• The first section presents all the currently available topologies to operate the network : ring, bus ( trunk or linear ), wireless topologies, and how to operate redundancy.
• The second section explains how to integrate the process network into an IP network systems and how to install such configurations : P-Net over Ethernet IP, over wireless IP networks and over Internet.
• The last section carries on wiring considerations.

www.proces-data.com

• Profibus-DP : Profibus for factory automation.

  www.profibus.org

The « Profinet-IO » network ( a Profinet bus specialized as a network talking with sensors and actuators ) seems not to be a topical question yet.

The solution used by the Siemens company to answer this need is the Interbus network, following a strategic deal with the Phoenix Contact company by merging their solutions. Nevertheless, to satisfy your curiosity, or whether you need it, you will take advantages by reading the introduction to Profinet IO provided by www.rtaautomation.com.