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In a single control cabinet

Modular electro-pneumatic automation system for hazardous areas
In a single control cabinet

Previously, control cabinets which combined electrical and pneumatic devices could not be used in Zone 1/21 environments. Too high were the risks of corroding electrical parts that could subsequently cause an explosion. The hybrid solution described below brings together electrical and pneumatic devices even in Zone 1/21 environments, achieving several advantages at the same time, such as less wiring, less planning and less documentation.

Werner Bennek

Until some years ago, combining electrical and pneumatic devices in Zone 1/21 environment control cabinets was hazardous due to the wet and oily compressed air, which caused corrosion and short-circuits. Today’s compressed air systems usually work with air qualities with a pressure dew point below -20 °C (residual moisture 0.88 g/m³) and an oil concentration of less than 1 mg/m³. Especially in the pharmaceutical and the food and beverage industries, the compressed air quality has improved by several orders of magnitude as a result. The quality of the exhausted compressed air is in fact so good that it can be channelled into the control cabinet in order to prevent humid, aggressive or dust-containing ambient air from entering. Pressure release with a climate socket or an exhauster is necessary, of course. Whilst working with dry and oil-free air reduces the problem of corrosion and short-circuits, there is still a detonation risk due to the process conditions.
Hybrid solutions combining electrical I/O systems with optional pneumatic outputs are state of the art for installations in safe environments or in Zone 2. Forming nodes, these electro-pneumatic systems connect numerous different electrical signals and pneumatic outputs with higher automation systems via a bus interface. However, mixing electrical and pneumatic devices in a single control cabinet for installation in Zone 1 hazardous areas remains a challenge. Bürkert has developed a hybrid so-lution suitable for installation in Zone 1 that unites its modular pneumatic automation system AirLine Ex 8650 with modules belonging to the Simatic ET 200iSP system from Siemens. This solution represents a complete, Atex certified unit.
Decentralised and standardised
The AirLine Ex 8650 unit is designed for decentralised operation and provides full support for this concept. It can be used in hazardous areas with a gas or dust atmosphere and is most valuable for process control in fine chemicals, pharmaceuticals and cosmetics or any other sector where solvents, alcohol or lacquers are utilised. In all these applications, the system is unique insofar as it allows EExi pneumatic valves to be integrated without additional wiring. By integrating the pneumatic functions, process and production sequences can be completely decentralised in an explosive environment. Standardised interfaces and the highly flexible and modular design guarantee fast and easy system set-up and enable pneumatic, electric and electronic modules with a variety of functions to be combined with one another. The components are connected by screwing and/or latching, thereby establishing both the electrical and the pneumatic connections. The pilot valves integrated in the pneumatic modules allow a wide range of different actuators to be controlled in the field, e.g. process valves or pneumatic cylinders. Explosion protection is guaranteed by limiting the voltage and current electronically. In conjunction with the intrinsically safe Simatic ET 200iSP system, all options for combined electrical and pneumatic so- lutions in Zone 1 hazardous areas, including extensive maintenance and diagnostic functions, are completely achievable and open.
Advantages at a glance
In Zone 1 hazardous areas, pneumatic control of cylinders and pneumatic actuators generally takes place either with single explosion-proof valves directly mounted to the actuator or with explosion-proof valve banks wired to a remote I/O system. In-stalling the pilot valves in the safe area is a further option – although often not pos-sible as the large distances between the valves and the actuators lead to unacceptably long switching times. However, connecting sensors and actuators to bus systems substantially reduces the wiring effort. Engineers and users of explosion-proof I/O systems alike therefore welcome integrated pneumatics and the accompanying advantages:
  • Installation close to the process
  • Reduced wiring
  • Compact design
  • Simplified documentation
  • Proven intrinsic safety
  • Low power consumption and therefore only little waste heat
  • Cost savings
The explosion-proof electro-pneumatic automation system also offers another important benefit – all elements, valves, etc. are harmonised and certified. This means that users are not obliged to demonstrate the safety of the system and Bürkert issues a single certificate for the complete control cabinet. On the contrary, they can be certain that all devices and elements are consistent with EN 60079 Part 0/1/7/11/26 and EN 60529.
Compliance with IP 54
At first sight, IP 54 only means “protected against dust and splashes of water”. However, as a control cabinet is defined as a category 1 device according to EN 60079–0, the test for dust protection has to be conducted at a defined low pressure over a certain period of time, as is normally only the case with IP 6x units. Non-certified components, like bulkhead fittings that are used in the context of the AirLine Ex 8650, have to pass an impact test at 7 J in addition to the IP 54 test.
According to EN 60079–11, all intrinsically safe connecting parts like clamps or plugs have to be explicitly labelled to distinguish them from non-intrinsically safe circuits. They are usually marked in light blue. If strip terminals with parallel intrinsically safe and non-intrinsically safe circuits need to be assembled, it is mandatory for uninsulated live elements of the different circuits to be kept a minimum of 50 mm apart.
Thermal heating
If a cabinet’s built-in components are operated at higher ambient temperatures than those for which they are approved, it is possible they could work for years without any effect on performance, even though they are actually a safety risk with regard to explosion protection. This needs to be considered in the design of the control system by attuning the power loss to the size of the housing surface, the maximum ambient temperature of the weakest component and the maximum ambient temperature of the cabinet location. After the cabinet has been assembled, a temperature measurement close to the weakest component is a must, of course.
Even if an Ex system only contains certified and audited components, the whole system has to undergo final testing to determine potential new sources of danger. What happens to the IP protection of the cabinet housing, for instance, if a tube breaks inside? Can the valves still be operated under vacuum conditions after the user has laid the tube into Zone 0? The above-mentioned examples clearly show the growing importance attached to certified subsystems, which help engineers, contractors and users concentrate on their main business by relieving them of the obligation to design and engineer control cabinets.
Bürkert Fluid Control Systems

cpp: It has been a number of years now since Bürkert first launched its AirLine Ex type 8650 electro-pneumatic system. What is the experience of users to date?
Bennek: In 2006, at the time of the market launch, there was still some way to go in terms of software. Back then, just EDD and GSD were available for start-up. These only allowed limited use of the many different functions of the ET 200iSP within STEP7 and PCS7. However, this shortcoming was quickly identified, and, working in partnership with Siemens, updates were soon made available to users. As the year 2008 draws to a close, the experience of users can be summed up in a single word: good. We have received positive feedback on configuration and start-up, these being the very areas where the seamless system offers big advantages. Where complete control cabinets were supplied, approvals and documentation have scored highly, with a single certificate instead of hours spent generating intrinsic safety documentation.
cpp: What solution does Bürkert offer for safe control cabinet integration of electrical and pneumatic components in potentially explosive environments?
Bennek: We need to differentiate here between the various kinds of potentially explosive environment. For applications in Zone 2/22 we have for a number of years also offered integrated solutions, consisting of our AirLine type 8644 system and the I/O systems from Siemens (ET 200S) and Wago (type 750). As an alternative to the above, I/O systems from other manufacturers have already been combined with a wide range of valve types in the form of a single valve or valve block. The safety of such superstructures is documented exclusively on the basis of temperature measurement within the control cabinet and corresponding verification of the maximum ambient temperatures of the internals. In the end, the user only receives a single manufacturer’s declaration with the corresponding Ex information, such as temperature classification, ambient temperature range, type of protection etc. Since the start of 2008, we have had the relevant certificates for our control cabinets, allowing us to offer systems for Zone 1 as well. All the above-mentioned control cabinet solutions can be used for applications in temperature classes T1 to T4.
cpp: Can we expect any further developments in electro-pneumatic automation solutions in 2009?
Bennek: We are currently working on extending our range to applications for Zone 21 as well. At the moment, there are no other further developments planned in this field.
cpp: What products will Bürkert be focusing on at Achema 2009?
Bennek: In contrast to the HMI, we will obviously be trying to meet visitor expectations at Achema with new solutions for the process industry. We are in a position to offer significantly more products and solutions for the pharmaceutical process industry this time round than we were three years ago.
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