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Sensors networks and measurement networks.

Sensors buses

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Automation > Resources > Techniques > Networks > Instruments networks

INSTRUMENTATION NETWORKS

Measurement buses, Vision systems networks.

Specialized Networks Dedicated To Measurement Devices

Instrumentation networks are specialized industrial communication networks allowing automation devices to exchange data with instruments, devices and other systems dedicated to the measurement and to analogical commands.

They can be measures transmitters, commands transmitters, or software applications used to adjust, to calibrate and to diagnose the instruments.


All of these measurement networks are used to communicate with sensors and actuators transducers.

Generally, their main purposes are firstly current data sending and receiving, and secondly setting the configuration, adjusting and calibrating the instruments and their interfaces.

Another important usage is the exchange of data for sensors and actuators maintenance and control.

Measurement Bus And Process Networks

DIN-MeßBus, GPIB - IEEE 488, Hart, LXI, M-Bus, Profibus-PA.

DIN-MESSBUS - The Measurement Bus

DIN-MeßBus features, Technical resources.

Low Cost Network Interface For Measuring And Testing

DIN-MESSBUS is a full duplex low cost network using a master-slave architecture which has been expressively designed for industrial measurement communication usages.

"DIN-MESSBUS" is also named "MEASUREMENT BUS" (the English translation from German language).

One of its particularity is that once the polling has started, a slave node can be disconnected and connected, an eventual interrupted data transfer will restart and continue without any data lose.

Its main characteristics are its simplicity, its robustness, its free topology, and the simplicity of its medium based on the so popular RS 485 standard.

Its message structure allow to transmit measurement values, configuration and diagnostic data.

Due to its flexibility and to its simplicity, "Din Messbus" is also used to carry quality data (for quality management), to process control and manufacturing control.

DIN-MEßBUS Features And Technology  

www.measurement-bus.de

DIN-MEßBUS Technical Papers And Resources  

(Archives)

GPIB (General Purpose Interface Bus), HP-IB and IEEE488

Technology overview.

A Standard Instrumentation Network For General Usages

The "IEEE-488" bus was developed to communicate with smart instruments (that is programmable), and to provide a standardized interface to exchange data between devices from different manufacturers.

The Hewlett-Packard company initiated the development of this versatile interface, and called it HP-IB (Hewlett Packard Instrumentation Bus).

Since HPIB became very popular, the "IEEE 488" commission renamed it GPIB (General Purpose Instrumentation Bus).

The IEEE 488 medium is a 24 twisted pairs (parallel cabling), 8 pairs of them are used by the data lines to transmit the data and the command messages (for a data length of 7 or 8 bits), 5 cables are used for the Bus management, and 3 cables are used for handshaking.

Later, the IEEE 488 has evolved leading the IEEE 488.2 version, with the integration of the SCPI interface (Standard Commands for Programmable Instruments interface), in order to avoid devices manufacturer extensions, and to provide a quite universal GPIB programming interface.

Introduction To The GPIB Technology  

HART - Highway Addressable Remote Transducer Protocol

What is Hart ?, Hart modem, Hart technology, Electronic interface, Educational papers, Quick introduction.

HART As A Communication Protocol For Industrial Instrumentation

HART ("Highway Addressable Remote Transducer") is a popular digital communication protocol designed for industrial process measurement applications, based on the 4-20 mA current loop standard.

The HART protocol has been especially designed to exchange configuration data, calibration data, adjustment data and diagnostic data. It is useful for installation and maintenance jobs.


HART consists in both a hardware protocol and a software protocol.


The HART technology benefits of the low noise characteristics of the 4-20 mA current loop, and do not need any other medium than the measurement transmission line, that leads in a cheap communication system.

Since HART uses rather low frequencies to modulate the signal, the transmission rate is quite low too, but it is not important because the purpose of HART is to exchange non time critical data.


The HART technology has evolved and is now available supporting wireless medium ("Wireless HART") and Ethernet medium ("HART-IP") too.

HART Modem  

A HART modem is used as an interface to enable the exchange of data between a terminal (computer, mobile terminal, programmable logic controller) and instrumentation devices such as a measurement sensors over a 4-20 mA current loop in compliance with the HART protocol.

The "HART modem" modulates and demodulates the signal in order to read and to write the data (which is the definition of a modem, indeed).

Terminal side, the data are carried over a serial communication port (RS232, USB, Bluetooth) which can be either a real port or a virtual serial port.

A HART modem allows an automation engineer to talk with a local sensor or to communicate with a remote sensor over ethernet.

Practically, the basic connection of a HART modem consists simply to insert a load resistor serially with the sensor into the current loop, after what it is enough to connect the modem in parallel of this resistor.

HART Communication Technologies  

Consultant in industrial control and communication, Romilly BOWDEN provides a whole of informations in relation with the HART technology.

You will learn what is HART in a short introduction, the revision history of the protocol, what were the main changes and a lot of other technical informations.


More, the author delivers H-SIM, a useful utility software which help you by computing the available cable length according to the desired strength of the signal you need for a specific installation of a HART network.

Romilly BOWDEN - www.romilly.co.uk

The Electronic Components Related To The HART Protocol  

This huge folder presents the available techniques in use to implement HART communications into hardware, and concentrates on the electric and electronic point of view.

In addition, the HART data exchanges process is explained clearly in a very detailed manner.

www.analogservices.com

HART Technical Papers  
HART Technology Overview  

The "HART Communication Foundation" provides short overviews about HART communication protocol, Wireless HART communication protocol, HART-IP Ethernet protocol, and presents the history of the protocols, what they are, and how they work.


In the technical articles section, you can download the "application guide", a 194 pages document quite well illustrated which presents quickly all the concepts in use and some industrial applications.

http://en.hartcomm.org

LXI - Network-based Extensions For Instrumentation

What is LXI ?, LXI basics, specifications and resources.

A Fast And Open Network For Instrumentation And Tests

LXI (Lan eXtension for Instruments) is an instrumentation network standard system particularly used for test instrumentation in research and development departments.


LXI is an evolution of the VXI / PXI systems which is based on the Ethernet standards, and which integrates the GPIB measurement capabilities.

LXI is GPIB compliant by networking through a dedicated gateway. In many ways, LXI is the successor of the GPIB bus.

Since it uses Ethernet, LXI benefits of the internet capabilities too, by embedding a web server into the instruments, interfacing and controlling them with a web application running on a cheap personal computer for instance.

Consequently, the devices do not need any front command panel any more, and the usage of popular and widespread technologies contribute to minimize the costs.

In order to provide an efficient synchronisation process, LXI uses the IEEE 1588 standard.


The inheritance of the VXI / PXI capabilities, of the Ethernet and internet features, of the GPIB measurement performances and of the IEEE 1588 services leads LXI to be a very powerful, fast, flexible, reliable and compact test equipment network system.


(*)  VXI (VME eXtension for Instrumentation) is a compact instrumentation network system which integrates the best features of both VME (Versa Module Eurocard) and GPIB buses.

(**) PXI (PCI eXtension for Instrumentation) is a more recent instrumentation bus system, which incorporates the leading characteristics of the PCI (Peripheral Component Interface) and of the GPIB buses altogether.

LXI Specifications And Technical Resources  

The LXI consortium promotes the LXI technology and is only too happy to offer many informations.

The "About LXI" section introduces to the technology (what is LXI ?, what are its benefits, what are its main features).

The "resources" section provides good introductions to LXI standard and some other guides. You can also download there some LXI technical papers and watch some videos. A few tools are available too.

Last but not least, you can download all the specifications freely, including the current version and older versions.

www.lxistandard.org

M-BUS / EN 13757 - The Meter Bus For Power Distribution

What is M-Bus ? , Meter-bus overview, Meter Bus technical documentation.

A Standard Network Interface For The Industry Of The Energy

"M-BUS" ("Meter Bus") is a specialized network dedicated to quite smart measurement devices, especially whose operating in the industry of energy and in the power distribution areas.

METER-BUS is particularly used to read consumption measurements at low cost.


There are several current available implementations, the last one supports wireless communications.

"M-bus" is a rather versatile network since it uses linear topology, star topology, tree topology or wireless network architecture, using a single master / slave structure and a client / server communication process.


One of its specificity is (or was) that the data telegram are not specified, letting the manufacturers free to define and to specify it.


In its wired versions, another "meter bus" specificity is that the master and the slaves modulate the signals over the power line in order to communicate.

METER-BUS Technical Overview  

This good overview about the wired system presents the "meter bus" data transmission system, the topologies, the "Meter-bus" trunk, applications and some related software.

www.baer-gmbh.com

Initial M-BUS Technical Documentation  

The "M-Bus" organization provides the complete M-bus V 4.8 technical documentation ( ), an old version in which you can learn the fundamental principles of the meter bus system.

www.m-bus.com

PROFIBUS-PA - Profibus For Process Automation

Profibus Alliance, Miscellaneous.

The Siemens Network For Automated Process  

www.profibus.org

Profibus-PA Technical Description  

This tutorial introduces the fundamental knowledge about Profibus in general, and the basic technology of "Profibus-PA".

It explains the physical layer, the data addressing, the safety layer, the topologies, the connections, the user interface and the device description interface (GSD files and EDD files).

www.samson.de

Vision Systems Networks

Cameralink, DCAM - IEEE 1394, GigE Vision.

Transferring Many Data In A Minimum Of Time

The specialized networks dedicated to vision computing offer structures providing high performances and data exchange interfaces well adapted to machine vision.


Images acquisition and images computing are greedy for bandwidth. They need to exchange a huge amount of data (the images) while vouching for very short responses time, depending of the applications requirements.

Whether images treatment is embedded in the vision sensor, the main constraint is the big amount of data to be exchanged, according to the amount of images the user wishes view inside a defined period, according to the frequency of archiving, and according to the amount of cameras in the network.

Whether images computing is external to images acquisition, it is necessary to transfer all the frames from the sensor down to the computing system in a moderate space of time, in a way warranting the delay from the time the acquisition has been done up to the time the devices are commanded.


National Instruments publishes an interesting article with considerations about the choice of the right camera bus.

CAMERALINK

"Camera link" basics, "Camera link" specification.

High Transfer Rate Camera Network Interface

"Camera link" is a hardware only specification designed by camera manufacturers to access cameras implemented in a network, in order to quickly read the frames and to control these cameras.

It is based on the "National Semiconductors" (nowadays "Texas Instruments") Channel Link interface.

The data transfer rate is typically about 2 Gbit/s in the basic configuration, and around 5.5 Gbit/s in the medium and full configuration.

The current "Camera link" specifications are provided by the AIA (www.visiononline.org), which maintains them.

CameraLink Technical Papers  
Camera Link Specifications  

Even these specifications could not be up to date, you will find all the informations you want about the Camera Link technology : the signals, the port assignments, the bit assignments according each available configuration and the description of the connections.

http://measure.feld.cvut.cz

DCAM, Firewire, IEEE 1394 - A Digital Camera Protocol

What is IEEE 1394 Firewire ? , Specifications and resources, Factory automation usage, IEEE 1394 basics, Hardware designers guide.

A Popular Bus For Digital Video Applications

The "IEEE 1394" standard protocol is also known as "DCAM" (Digital CAMera protocol), "IIDC" (Instrumentation and Industrial Digital Camera), "Firewire", "iLink" or "I-Link".

Firewire is a high speed serial bus designed for digital audio and video consumer usages.

It has been originally developed by the Apple company, and is quite the concurrent of the USB technology.

The "Firewire" bus operates both isochronous and asynchronous data transfers, what leads to real time capabilities.

However, its features are compliant with industrial usages in order to operate machine vision installations at low cost, according to its performances.

IEEE 1394 Specifications And Useful Resources  

Damien DOUXCHAMPS is an engineer particularly involved in the world of the digital cameras and in the world of the "IEEE 1394" standard.

He provides a lot of informations and some useful utilities related to the digital video devices.


Damien DOUXCHAMPS - http://damien.douxchamps.net

Using Firewire In Industrial Automation  

These slides show how compliant can be "IEEE 1394" for industrial applications such as imaging, industrial fieldbus, motion control and remote sensors access.

This document compares some features of the IEEE 1394 and GigeVision standards (the topology, the performances, the usability, the hardware requirements), and why the IEEE 1394 is reliable for automation networking, especially concerning the "IEEE 1394b" version of the standard.

(Archives)

IEEE 1394 Fundamental Knowledge  
IEEE 1394 Hardware Designer Guide  

This document presents many considerations related to the system design, the cable power, the link selection, the firmware layers and more.

(Archives)

GIGE VISION - Gigabit Ethernet For Vision Systems

What is Gige Vision? , Gige Vision Overview.

"Gige Vision" As A High Performing Data Exchange Interface

"GIGE VISION" (Gigabit Ethernet Vision) is a high performing specialized network system dedicated to machine vision and more generally to image transfer, intended to interface cameras from different manufacturers with any other devices and with any user applications.


The Gige Vision standard is based on the Gigabit Ethernet specifications, and later probably on the 10 Gigabit Ethernet specifications.

"Gige Vision" networks work using UDP (User Datagram Protocol), rather than using TCP (Transport Control Protocol).


The Gige Vision protocol is divided in four parts.


Introduction to "Gige Vision"  

This comprehensive "Gige Vision" overview presents what is Gige Vision and why Gige Vision exists.

Then it describes how "Gige Vision" is structured according to the OSI layer standard, it resumes how to connect a Gige Vision Camera to a personal computer and how do multi-camera applications work.

Finally, it compares the Gige Vision Camera features and costs with cameras using different interfaces according to various configurations.

www.i2s-vision.fr

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