Steve Leech from Siemens Industry Automation shows how bringing IO signals from hazardous areas to a distributed control system offers benefits in terms of reduced capital expenditure and increased operational efficiency

Many process industries have to overcome the obstacles presented by hazardous operating areas. Often the manufacture, processing, transport or storage of combustible materials can result in the creation or release of gases, vapors or mist into the environment. Because of this careful consideration must be applied to the safe use of equipment in such problematic areas, for instance distributed automation solutions.

Applications that commonly create the potential for explosion present issues that need to be overcome, particularly with the necessity to bring IO signals from hazardous areas back to a distributed control system. With ATEX legislation governing the rating for components in hazardous areas, a traditional approach to the problem has been commonly adopted.

This has involved the installation of IO housed in a safe zone in conjunction with hazardous area barriers that are hardwired to allow signals to be passed into the affected zone.  This entails significant capital expenditure cost as IO, barriers, components and hard wiring over long distances have an impact on both installation costs, and onward operational efficiency.

An alternative approach

An alternative approach that tackles such issues is the use of technology that can be installed directly into the hazardous area and which negates the need for barriers and hard-wiring at installation phases.  It can also be configured during normal operation, and offers hot swapping and diagnostic and redundancy capabilities.

At the centre of this alternative approach lies the modular based ET200iSP field device system, designed for use under hazardous ambient conditions. The station can be used in different hazardous specified zones as described in directives EN 60079-10 and EN 61241 -10,  either in Zones 2 and 1 in the case of gaseous atmospheres, or in Zones 22 and 21 in the case of dusty atmospheres and the connected sensors and actuators located in Zones 0 and 20.  The open and standardized system uses Profibus DP to link communication on a local level between the field devices and the process control system.  Use of an isolating transformer makes Profibus DP intrinsically safe, which is achieved by isolating the bus and limiting the energy in the safe area.

Running a single Profibus cable connection to locally mounted IO reduces installation hard wiring cost and time, as there is no need for terminal blocks, distribution boards and IS barriers for the IO signals.

Flexible installation

For instances of retrofit where space can often be at a premium, the ability to use a standardized, fully certified control cabinet mounted solution allows a more flexible installation solution in the field. This reduces hardware installation levels and overall system risk. 

Along with the infrastructure benefits that works with space restraint, complies with hazardous zones needs and reduces wiring levels, the intelligent system also provides operational benefits once up and running. 

Downtime can be cut as diagnostic information is generated as internal or external faults occur, allowing informed decisions to be taken or ongoing proactive maintenance programmes adopted. With high system availability a pre-requisite, the independent wiring supports easy, reliable replacement of modules during normal operation, and the ET 200iSP can also accommodate hot swapping of the power supply without arcing, as well as redundancy.   Stations can be added or expanded with modules, or module parameters can be changed during normal operation – again, maximizing operational efficiencies and production control.

Recent examples of the ET 200iSP in action include  its use at a major UK drinks manufacture, where it has driven production efficiencies and flexibility and set it on course for a standardized approach for the future industrial automation technology across its plant.  Gordon Fleming from Solution Partner, Kigtek said: “The ET200iSP panel came pre-glanded and pre-designed and alleviated the need for third party certification processes and ensured that all necessary installation and connection was simple and speedy – again helping drive cost efficiencies. We would estimate that, for example, engineering cost savings equating to 1 to 2 days is achievable per panel and up to 10% of installation costs can be reduced as a result of locating the ET 200iSP IO system closer to the field devices.”

A fine saving

Fine Organics – a manufacturer of fine chemicals for the pharmaceutical, agrochemicals and speciality chemicals markets – has also derived benefits from the implementation of the ET 200iSP.  As part of a recently installed PCS7 distributed control system at its Seal Sands production site, the company is benefiting from device’s  installation, flexibility and unique SIL rated IO advantages.  With chemical process vessels spread across its production site, Fine Organics has been able to locate the iSP close to these vessels, and link them via Profibus  back to the main control system – without worrying about performance and suitability for such potentially hazardous areas and raw materials. The company was faced with a one off installation cost, but then just subsequent short cable runs from the vessel to the safety box in situ. The enhanced diagnostic capability and the cost benefits of quicker and simpler installation has offered Fine Organics ongoing capital expenditure and operational benefits.  

Julian Lightwing from Fine Organics, said:  “We are constantly changing our production schedules and products to meet market demands and having an intrinsically safe field device and standardized control system that can operate in a challenging environment and is straightforward and low cost when we need to modify is a real benefit for us going forward.”

Siemens Industry Automation

T: 0845 770 5070