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The basic idea of explosion protection is to protect man and environment by means of safe components, systems and equipment. The explosion-proof design of motors, controls and switchgears, electrical automationequipment, analytical systems and measuring systems or devices and components for heat technology is of the same importance as the application of explosion-proof installation and connection technology. Especially control, command and signalling devices have to be adjusted to a variety of requirements of individual users in different sectors. Thiscan be achieved by consistent modularisation – from end switches to limit value transmitters, command and indicator devices to control unitsand fieldbus systems. Modularity allows to consistently combine individual control and connection modules in view of the users´ requirements and to generate complete solution systems.
End switch:
Pressure-proof encapsulation of ignition spark
Explosion-proof end switches are used in applications where a safe and reliable signal indication is required. Even if manufacturers of complex machines and systems consider these end switches as components of their solutions, they are not components in terms of explosion protection but devices, fulfilling an essential safety-related and functional task. Devices inthe terms of ATEX RL 94/9/EG have an independent function, that is, they can be applied as stand-alone units – unlike the components that are also described in the guideline, such as block terminals, individualswitching modules and luminous modules, that can be integrated – withappropriate protection – into devices and systems without any furthertest.
Even the miniature micro-switch - smaller than a sugarcube - is a device. This can be seen on the CE labelling attached to the outside, the number of the EC type approval certificate and the temperature class. These switches, whose electric connection is cast intothe rear side, are applied in places where there is hardly any room for an explosion-proof switching element. They are especially suited for being applied in valves, thermostats, pressure switches, final controlling elements, filling level meters and switching devices. This minuscule Ex d micro-switch demonstrates the explosion protection philosophy of all these Bartec devices. The pressure-proof encapsulation (Ex d) directly encapsulates the ignition spark. As the explosion protection becomes effective right at the place where the explosion hazard develops, the encapsulation requires a low volume and therefore a small installation size – suitable for explosion-proof design of compact devices such as position sensors and switches or magnetic switches.
One application example for explosion-proof micro-switches are limitvalue transmitters. They are applied in conjunction with pneumatic actuators on fittings for the signal recording of the status “Open/Closed”. For most of the versions, this final position feedback takes placevia pressure-proof encapsulated end switches with appropriate connection and attachment parts. Limit value transmitters can be applied in explosion-hazardous environments of zones 1 and 2 in accordance with thecertified explosion subcategories IIA, IIB and IIC and temperature classT5/T6 as well as in zones 21 and 22 in accordance with the certified maximal surface temperature.
Command and indicating devices:
flexible as standard
The principle of modular explosion protection is continued in the command and alarm devices of the ComEx series. ComEx adheres to a flexible system concept allowing the realisation of standardised as well as customised on-site command and indicating devices. Three shock and impact proof polyamid standard housings areavailable; up to three different command and alarm devices can be built into them. Up to three housings can be combined with each other – an option which also applies to the robust and corrosion-proof stainless steel housing. The operating and monitoring functions are availableas pre-configured complete devices, e.g. with a signal lamp and two push buttons. Pursuant the idea of modularity, these functions can alsobe arranged in a customised or application-specific way. Almost 50 different actuator elements and installation modules such as push buttons, switches, selector switches, locks, indicator lamps, potentiometersor measuring devices are available in nearly any combination. The systems cover an ambient temperature range from -55 to 55°C. They are applied for operating and monitoring machines, processes, drives, pumps,rolling gates, process engineering systems, etc.
On-site control points:
Standard bus into the explosion-hazardous area
Ifthe operating and monitoring requirements on the system become more complex and if additional control functions should be realised, ComEx is the basis for explosion-proof, decentralised on-site control points.At these control points for the application in explosive areas, command, alarm and indicating devices and bus interface modules are integrated depending on the technical requirements – if required, under inclusion of controls and the complete wiring on series terminals. Depending on the version, they are mounted either on mounting rails or into the front side.
The housings are designed in accordance with the requirements of ignition protection type ‘increased safety’. Depending onthe specification and quantity of the equipment, different housing types and different sizes are available. For on-site control points in explosion-hazardous areas with combustible dusts, the ignition protection type ‘protection by housing’ is applied.
The Modex series comprises these explosion-protected, decentralised on-site control points, furthermore. it is also the trademark of the bus modules applied there. Due to the combination of ignition protection types, they allowto direct standard bus systems continuously from the safe area to theexplosion-hazardous area. This is why not only intrinsically safe components with low power requirement can be integrated into the fieldbusstructure, but also non-intrinsically safe motors, valves or heating systems which require considerably higher performances than could be achieved with intrinsically safe circuits. Therefore Modex bus modules offer a variety of advantages, among others less space required in thecontrol stand, omission of I/O level, Ex separation as well as main distributors and field distributors, avoidance of complicated serial wiring or parallel wiring, and higher flexibility in planning and engineering. Altogether, the variety of different modules – like barriers, relays, contactors, fuses, measuring transducers, power supply units andisolating units – allows to realise flexible solutions for differenttasks and requirements.
‘More Profibus’ in the explosion-hazardous area
Modex does not only take the standard bus, e.g. Profibus, into the explosion-hazardous area – different modules also allow amigration of the existing bus environment. The Profibus DP coupler and the Profibus DP repeater, which are specifically designed for the industrial requirements of the explosion-hazardous area of zone 1, allowto separate or generate new segments. Among other possibilities, thenumber of participants at the bus can be increased and the segments can be cascaded to increase the coverage range. In the end complex, openand flexible star-shaped and tree-shaped structures develop from theRS485 typical linear structure. Moreover, the devices allow a duplication of the signal in order to realise a redundant connection to a master.
If signals in the Profibus have to be transmitted interference-free over large distances at high speeds, copper lines reach their electromagnetic limits even if they are correctly shielded, wired and installed. By means of the LWL ring couplers and PP couplers RS485/Profibus, the Profibus is transposed from copper lines to optical waveguides (LWL), offering considerable advantages with regard to interference resistance, speed and coverage - up to 2,600m are possible. Both the ring coupler and the PP coupler are available for the application in zone1 or, respectively, for zone 2 and non-explosive areas. The electronics for signal conversion gets a pressure-proof encapsulation forzone 1 by the Modex housing. Transmitter and receiver for the opticalwaveguide are activated in an intrinsically safe way for the version in zone 1. This guarantees that the transmitter does not reach inadmissibly high transmitting power values. For the optical waveguide couplers of zone 2 and in safe areas, the transmitting power is also limitedin order to guarantee the compatibility with the devices of zone 1.
Whether components solution or complete solution: the requirementof communication with equipment, machines and systems for operation and monitoring or data transmission does not stop at the explosion-hazardous area. The multiple requirements occurring in practice can best be met, in technical as well as in economic terms, by means of a consistent modularisation.
By Johannes Buhn and Klaus Marth, Bartec Safe.t Academy
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