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Explosion-proof contacts

System solutions using bus and interface components
Explosion-proof contacts

Wiring systems for process engineering in-volves a considerable amount of time and effort because of the large number of sensors and actuators. The installation of explosion-proof and non-explosion-proof components is simplified by the use of advanced bus and interface components.

Paul Maluck

Nowadays, economic efficiency constitutes an absolute must in designing the signal transmissions in process-engineering systems. Compactness and clarity in the layout ensure low initial costs and less space is required. In addition this, the vol-ume of planning and documentation needed is reduced, fault diagnostics are simplified and the system’s availability is increased. Innovative products for routing, signal adaptation and serial signal transmission in the field are needed, both for extending existing facilities and for building new installations.
Combined routing and signal isolation
Routing systems in process engineering always involve a considerable amount of time and work for designers, builders and users alike. In view of the large number of sensors and actuators in process engineering systems, the routing level takes up a considerable amount of the space in the switching or maintenance room. If the units installed in the field are located in a section of the plant designated as explosion-proof, then „intrinsically safe“ is the class required for explo-sion protection. Barriers, buffer stages and/or isolating amplifiers that meet the requirements for the EEx i type of protection (intrinsically safe) must be installed in addition. The expenditure for planning and installation increases as a result. Modular isolators, multiple-channel motherboards or multiple-channel 190 plug-in cards are usually suitable for explosion-proof isola-tion. They are installed in separate switching cabinets and isolated from the routing. The amount of space needed at the routing level and at the interface or isolation level are often quite different. The connections for the field signals hence require less space at the routing level than is the case at the interface and isolation level.
Savings in conventional parallel wiring are possible by optimising the routing and interface level as well as by compactness in the design of the switching cabinet. The narrow process-interface isolation terminal – just 12.4 mm wide – shown in Figure 1 and a series of plug-in, electronic, isolation modules have been developed to meet user demands for clarity, flexibility and easy maintenance. The space required by the process interface component is equivalent to that needed by two single terminals each with a cross-section of 2.5 mm².
The process interface components have a basic terminal with an integrated isolating blade as well as test sockets before and after the blade isolation, as the basis for estab-lishing the connection. The blade isolation allows the signal path to be interrupted quickly and unambiguously for maintenance purposes. Measuring equipment can be connected into the current loop at any time at the test sockets. Jumper plugs transfer the power safely and reliably from one module to the next. The process interface components also fulfil all the criteria demanded of convenient terminals with regard to standard inscription materials, bridging and testing possibilities etc.
The basic terminal can be mounted directly on a standard DIN rail. The self-coding plug-in electronics are subsequently connected to this basic terminal. They ensure both electrical isolation and signal conversion between explosion-proof and non-explosion-proof areas. Following signal conditioning, the user can determine the size of the routing level and the additional components needed for routing. Necessary reserves can be planned as early as the installation stage for the basic terminal on the DIN rail in the switching cabinet. If necessary, a suitable isolating module can be subsequently mounted on the basic terminal, in which case the isolating module is coded at the same time (Fig. 2).
Integration saves space and costs
On the one hand, integrating the plug-in process-interface isolating terminal in the routing cabinet ensures an optimum ratio be-tween the field and interface isolating levels, while on the other hand the switching cabinet where the signal conditioning equipment is normally accommodated is no longer needed. This eliminates additional terminal points and saves both space and money. The range of plug-in, explosion-proof electronic products consists of smart-compatible feed isolators, Namur switching amplifiers, valve control modules, isolating amplifiers and temperature measurement converters for thermocouples/resistance thermometers. The explosion-proof modules with the „intrinsically safe“ type of protection are certified according to the latest European Atex directives.
Freely configurable input and output isolators are available for non-explosion-proof applications. These universal modules re-‚duce the inventory and module diversity for different signal combinations to a minimum. The user can set the signal combination required in each case with the DIP switch integrated in the side of the housing. A variety of interfaces and solutions are available for conventional wiring to the control system, to the PLC or to other control systems.
Serial processing of field signals
Interbus is the serial signal transmission system for explosion-proof and non-explosion-proof areas in the process engineering industry. Some 150 000 applications are currently installed. New developments and system extensions that are adapted to the particular requirements of each application are evolving in close collaboration with designers, plant builders, operators and end customers.
One of these developments is Interbus Process I/O. This is a modular system that is simply connected into the Interbus topology as a bus device, making the I/O level avail-able for connecting both intrinsically safe signals from the explosion-proof area and non-explosion-proof signals. The modular system comprises a basic module carrier with plug-in Interbus head-end, four or eight-channel, plug-in, analogue and digital input and output modules as well as various interchangeable terminal blocks for each input and output module.
Interbus Process I/O is suitable for applica-tions in both explosion-proof areas (Zone 2) and non-explosion-proof areas. The system can be installed in a wide range of industrial environments on account of its very robust modular construction as well as its re-sistance to vibrations, shocks and aggressive atmospheres (Fig. 3).
Interbus is already used today for many applications in explosion-proof areas (Zone 1), whereby both powerful field devices (solenoid valves, etc.) with increased safety (Ex e) and intrinsically safe sensor and actuator systems can be directly connected to Interbus Modex modules in Zone 1. Interbus thus allows new, extended and converted systems to continue using all the proven field devices previously in service. The demands by the process engineering industry to incorporate the PLC and lower-level systems in the existing process control systems and visualisation concepts are also fulfilled by Interbus, thanks to the flexibility of its direct connections and the option of linking up to Ethernet systems based on TCP/IP.
Gateways to the standard interfaces of the Modbus process control systems and Ethernet TCP/IP, the de facto standard, are available for using Interbus in process engineering plants. The first applications with Freelance 2000 from EB Hartmann & Braun are currently being installed. Customers value the straightforward handling principle of Interbus’s integration in the process engineering. ABB, Honeywell, Philips, Siemens, Proleit and many earlier control systems have al-ready been linked in for several years using Modbus gateways.
Phoenix Contact
Fax: ++49/5235/341200
Further information about the process
interface in cpp-277
Further information about the Interbus
Process I/O in cpp-278
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