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| Central and decentral expansion
>> Networking easy800 over distances of 1000 m >> by Ronny Happ General >> Almost all contemporary automation solutions currently available require a communication bus or a information network in order to guarantee cost-effective decentralization. This is useful not only for complex control tasks, but also for smaller applications from a technical and economic point of view. In order to optimally use the advantages of decentralization, it is essential that the decentral nodes and stations also posess a certain amount of intelligence. The load on the communication network used can be thus reduced and the fieldbus which is applied is guaranteed a good deterministic behaviour.
The Moeller easy600 and easy800 control relay family are predestined for these tasks. The easy800 family offers the optimum requirements for control tasks in building engineering, mechanical engineering and device engineering fields with its logical and arithmetical functions as well as its diverse timer, counting and switching functions. With its integral NET network, the easy800 offers the control relay a comfortable, simple and cost-effective method for decentral networking of up to 8 network users. Furthermore, the easyLink interface which is well-known from the easy600 family provides the control relay with the option of locally expanding the number of inputs and outputs as well as a coupling module to the most popular fieldbus systems. |
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| Networking via the easy-Link interface >>
The easy800 control relay offers – as does the smaller easy600 family – an easy-Link interface for local expansion of the device. The expansion devices are simply connected directly to the basic unit via the supplied plug connector (Fig. 1).
 Figure 1 With the aid of the easy200-easy coupling module from Moeller, relatively inexpensive decentral I/O expansions up to 100 m (30 m are guaranteed by Moeller) can be implemented.  Figure 2 In addition, this interface offers the possibility of connection to common fieldbus systems such as CANopen, DeviceNet, ASi and Profibus DP via a diverse range of communication modules. With these modules, it is ultimately possible to integrate the control relay in complex automation solutions. By selecting one of the fieldbus systems on offer here, the easy control relay can be used as an intelligent node in a communication network with master or button based control. 
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Figure 4
When examined from the point of view of the ISO/OSI reference model, the physical and data security layers of the NET network protocol correspond exactly with the CAN protocol. For this reason, the considerations with regard to data transmission speeds and the associated maximum bus expansion apply. 
Figure 5
The commonly available CAN physical transmission media can be used for the hardware-based implementation as well as for the engineering of an NET - communication bus. However, special demands are placed on the copper cables with a bus length of a possible 1000m. Additionally, the transmission speed must be drastically reduced (see AWA and manual for easy800). A technical alternative to copper cables is offered however by fiber-optic cables. A much greater expansion of the bus can be achieved with the aid of two copper/fiber-optic cable converters (CU-FO) and the respective fiber-optic conductor between the repeaters. A CU-FO converter of this type is offered by IXXAT.  Costs of networking >> Of course every automation solution has its price. The design engineer who is involved in planning a system is also responsible for this price. It is therefore essential that a critical examination of the costs and benefits is undertaken to justify use of the network selected. The prices listed in the following are only intended to provide a rough guideline of the implementation of a communication fieldbus based on copper cables or on an alternative fiber-optic system. |
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