Further to my previous article on calculating an Intrinsically Safe loop approval (http://www.instrumentation.co.za/7571a ), we consider the impact of Exic and how to handle long cable runs in IS loops.
Archive for Technical Papers
As wireless devices such as mobile phones and laptop computers become more reliable and cost effective, there is growing interest amongst the process industry as to the benefits to be found from enabling such devices to be used in hazardous areas. However, unlike most industries this is not a simple task. Installing wireless networks in hazardous areas requires careful, expert planning and execucution. John Hartley, Managing Director of Extronics, explains the hazards posed by radio frequency sources and the issues involved when installing wireless networks in hazardous areas, and how to minimise the potential risk.
For an explosion, all three of gas/dust, oxygen and source of ignition (spark or heat) need to be present. Intrinsic Safety works on the principle of removing the source of ignition. This can be achieved by using a Zener Barrier or Galvanic Isolator.
The protection of electrical apparatus for use in flammable atmospheres is embracing a new technique: Ex ic. As a logical extension of the existing intrinsic safety concept, it formalises the application of intrinsic safety in Zone 2 hazardous areas, but users and manufacturers alike are wrestling with the details. The discussion centres as much on the withdrawal of the Ex nL technique, as on the application of Ex ic which replaces it. The paper deals primarily with the impact on countries that follow IEC and ATEX practice, but there are parallels with the ‘non- incendive’ technique that is adopted in North America.