Intrinsically Safe Fiber Optic Communication Bridges Middle Distances in Profibus DP Networks
30 May 2008
Fiber optic lines are capable of bridging more than ten times the distance provided by copper cables, enabling users to transfer signals with the same bandwidth from Profibus DP field devices via distances of 2km or more. Intrinsically safe ISpac 9186 type isolating repeaters even allow for communication between hazardous and safe areas. If required, the isolating repeaters can also be used to implement ring structures, ensuring high availability through the redundant route. Problems such as insufficient potential equalization, which can occur in Profibus cables with screen grounding, are ruled out on principle. Moreover, the light waves are not affected by electromagnetic interference from devices within and outside of the network. The only restrictions users face are installation requirements, such as maximum bending radius, acceptable strain and compression, and, if required, the necessary explosion protection against light as an ignition source.
The protection type “optical intrinsic safety” (Ex op is) is particularly suited for that purpose – it not only ensures a safe limitation of optical energy per unit area, but also allows for particularly easy installation. ISpac 9186 type isolating repeaters feature Ex i and Ex op is protected data transmission interfaces. Therefore, the electric RS 485 plug and the fiber optic connection can be connected and disconnected at any time under load (without switching off the laser diode).
Additionally, the easy-to-use isolating repeaters feature a unique diagnosis function which constantly analyzes the level of the received optical signal, displaying it via an LED bar at the unit's front side. This allows users to determine the quality of the received signal at one glance, without using measuring equipment. If the receive level reaches a critical area, the isolating repeater reports that status via a potential-free contact. Thereby, impending failures can be displayed for maintenance staff in due time.
Apart from models suitable for zone 1, R. STAHL also provides isolating repeaters for zone 2 and safe areas. The units are designed as system components – as such, they complement R. STAHL's other solutions for connecting field devices. Supporting a large number of fieldbuses (Profibus DP, Modbus, HART RS-485 and R. STAHL ServiceBus), they especially enhance the flexibility and applicability of the IS1 remote I/O system.
