Instrumentation • Electronics
4 Connecting sensors to a control system by means of a network offers significant time and cost savings over using traditional hard-wiring. Furthermore, as Alistair Rae reports, integrators and end uses can also benefit from a more intelligent control system and improved performance of the overall process.
4 La connexion de capteurs à un système de contrôle par l’intermédiaire d’un réseau offre d’importants avantages en termes de temps et de coûts, par rapport à des liaisons conventionnelles en cuivre. De plus, comme l’indique le rapport d’Alistair Rae, les intégrateurs et les utilisateurs finaux peuvent aussi bénéficier d’un système de contrôle plus intelligent et d’une performance accrue sur l’ensemble du processus.
4 Durch den Anschluss von Sensoren an ein Steuersystem über ein Netzwerk können im Vergleich mit herkömmlicher Verdrahtung signifikante Zeit- und Kostenersparnisse erzielt werden. Wie Alistair Rae herausfand, können Integratoren und Endnutzer außerdem von einem intelligenteren Steuersystem und verbesserter Leistung des gesamten Prozesses profitieren.
Sensor networking provides scope for intelligent control
S
ensor data transmission has come a long way since the days of simple digital (on/off) machine control, hardwired analogue signals, and RS-232, RS-422 and RS-485 serial
protocols. With so many alternative networking technologies from which to choose, engineers seeking the optimum for an application must consider what their requirements are - and whether the sensors they need are available with the necessary networking capability. The actuator/sensor interface (ASI), developed
by a consortium of European automation companies which saw a need for networking the simplest devices at the lowest level, offers the dual advantages of simple configuration and low cost. ASI is designed for small systems employing discrete I/O (input and output) devices; it caters for a maximum of 31 slaves, which can provide for up to four inputs and four outputs each for a total of 248 I/O (Fig. 1).
ASI is typically used to connect proximity
sensors, vision sensors, limit switches, valves and indicators in equipment such as packaging machines and material handling systems. For more complex networking, engineers today
can select from a broad range of fieldbus protocols. In some cases an engineer’s choice of sensor manufacturer will determine the protocol, and there are currently two consortia trying to encourage manufacturers to use their technologies: FDT Group and IO-Link.
Historically, Field Device Tool (FDT) technology was associated with factory automation users and vendors of discrete manufacturing equipment such as ABB, Endress+Hauser, Invensys, Metso and Siemens. Following the publication of an international standard, IEC 62453, Field device tool (FDT) interface specification, FDT is claimed to be platform-independent and supports a multitude of protocols including Hart, Profibus, Foundation Fieldbus, Devicenet, Interbus, AS- Interface and Profinet. FDT standardises the communication and
configuration interface between field devices and host systems. Moreover, it provides a common environment for accessing the devices’ most sophisticated features; any device can be configured, operated, monitored and maintained through the standardised user interface, regardless of the supplier, type or communication protocol.
Point-to-point connections
IO-Link is an intelligent point-to-point connection system at the field level, which is compatible with existing I/O standards and is supported by a consortium of automation product suppliers. These companies have come together to support what has been described as a new concept in all areas of sensor, actuator and control technology. According to the consortium, IO-Link promises
16
www.engineerlive.com Fig. 1. IFM, a co-founder of ASI, continues to develop new products such as this AC5230
active slave module that handles standard analogue (4-20 mA) current inputs and outputs.
simplified installation by replacing parallel wiring and various types of analogue signals with IO-Link. Also included are function modules for automated parameter setting and tool-assisted parameter setting, as well as remote diagnostics down to the field device level, cable break detection and device- specific diagnostics. Additional sensor information can be accessed with minimal effort in terms of hardware and software. To see the benefits of IO-Link, consider a packaging system equipped with a colour sensor. A sensor is normally connected using an industry- standard M12 eight-pin connector; termination is expensive and time-consuming, and connecting cables are rarely available pre-assembled - meaning that in-house cable assembly is required. It is therefore inevitable that mistakes are occasionally made, which have to be identified and remedied. In contrast, with IO-Link a sensor is installed and electrically connected using a standard, readily available M12 three-pin connector. This eliminates
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60