Intrinsic safety is the simplest and most cost-effective approach to ensure the safety of Hazardous Areas, industrial environments where a risk of explosion exists due to the presence of flammable and combustible materials and potential ignition sources.
Rules about equipment and protective systems intended for use in these areas are set out by ATEX Directive 2014/34/EU, which in 2016 replaced Directive 94/9/EC with minor changes. Intrinsic safety devices are the only kind of products ATEX standards admit into 0 Zones (classified at greater risk).
There are 2 main types of intrinsically safe barriers:
- Zener barriers;
- Galvanically Isolated Barriers (or Galvanic isolators).
What are the differences between them? How can you choose the best barrier for a particular plant? Here are some characteristics and parameters to consider.
How do intrinsically safe barriers work?
Intrinsic safety’s basic principle consists in limiting the levels of energy present in the circuits, so as to avoid the ignition of the potentially explosive mixture, even in case of failure. The two types of barrier perform this task in different ways: Zener barriers divert excess energy to earth through the fuse and Zener diodes, while Galvanic isolators provide isolation between the circuits in the hazardous area and those in the safe area, using relays, transformers and optoisolators.
Installation, cost and size
Zener barriers are simpler and cheaper systems compared to Galvanic isolators. They are also normally smaller in size.
Zener barriers need a good dedicated and redundant ground connection, which must have a resistance of less than 1 ohm. Furthermore, the apparatus in the hazardous area must be isolated from the ground to ensure safety. If the fuse burns, it must be replaced. Galvanic isolators, instead, don’t need ground connection nor maintenance, and by their nature the field apparatus can be grounded.
Which is the best solution?
There’s no need to say that the choice of the type of intrinsically safe barrier must be based on single plant’s characteristics. However, the general market trend in the market is to abandon Zener diode barriers (more traditional solutions) and to prefer Galvanic isolators, which among other advantages ensure lower installation costs, greater precision, the possibility to use sensors connected to the structural ground of the system, full voltage available to field devices and high rejection to common mode disorders.