The Fieldbus System for explosive Areas
Various fieldbus systems are used in different sectors of industry. This is because each sector has special requirements that are not fulfilled by each system. The field intrinsically safe concept (abbreviated as FISCO) exists for the sector where there is a high risk of an explosion, namely chemistry or physics.
This concept shall ensure that nothing happens in these very hazardous sectors of industry. If there was uniform system, it is possible that certain safety gaps might not be recognized and it might not be possible to guarantee of safety standards for each industrial execution. This is different with the field intrinsically safe concept. This concept conforms to the DIN standard: DIN EN 60079-27 (VDE 0170-27):2008-12 as such, it is officially recognized.
The History of the Field Intrinsically Safe Concept
The concept was developed in the middle of the 90s by different parties. On the one hand, the Physikalisch Technische Bundesanstalt participated in the development and on the other hand, it was joined by ABB and the chemical industry. Furthermore, the Profibus organization for technological support has been a part of the development of the Field Intrinsically Safe Concept. Over the years, the concept has changed again and again. Since 2001, the Fieldbus foundation has also been part of the development group.
Advantages of the FISCO System Application
This system offers the user certain advantages when using the Field Intrinsically Safe Concept in a highly explosive area. One of the most important items is the fact that the plug & play solution can be used in hazardous situations or areas so that quick action is possible very easily. Furthermore, the concept does not require any system certification at all, as such, the work progresses faster. Most alternative systems are complicated in installation and setup.
The Field Intrinsically Safe Concept is a simple expansion of the system, which can be used quickly and easily. The max. number of devices that can be connected is very high, so that the costs are reduced very much. This is something which is very important in the industry and in science, as the budget in most cases is very limited. The last advantage of the Field Intrinsically Safe Concept is the fact that no new calculations are required when devices are replaced. This is very work-intensive and requires time and money.
About the Requirements for this System
The FISCO system has several criteria that must be met. It is very important that the devices which are used have all been certified in accordance with FISCO, which means that they require the typical CE test certificate. When such a certificate is required, one of the following institutes should be contacted:
- PTB
- BVS
- KEMA
- FM
- CSA
These institutes can certify devices in accordance with FISCO, and it is only then that they can really be used with the Field Intrinsically Safe Concept. In all other cases, the high safety of the system is not assured, as the compatibility has not been checked and certified by professional experts. Ui, Ii, Pi applies to each of the field devices to be operated with this concept. U0 smaller than Ui smaller than I0 smaller than P0 smaller than Pi. The functionality of the system is only guaranteed when these criteria are satisfied.
The required cable parameters must also be met. This means that R, L, and C all must be equal to the fieldbus cable type A. A further requirement for the Field Intrinsically Safe Concept is that the line connections must be correct. If this is not the case, safety is no longer assured and the system does not function as intended.
It is important that the total length of a PROFIBUS or FOUNDATION fieldbus H1 line including the stubs is max. 1000 m. There are exceptions, but they only apply for multi-barriers. The max. length of the PROFIBUS PA or FOUNDATION fieldbus H1 line including the stubs can then reach 1900 m. Strict care should be taken that these specified lengths are not exceeded. This way, the system functions as intended and the safety during the industrial process is not endangered.
Securing of Intrinsic Safety
For each fieldbus component to be safe, there are diverse measures that must be taken with the Field Intrinsically Safe Concept. For example, it is essential that there is only one energy supply per element. The cable lengths and the cable types should also be specified accurately.
Furthermore, while a station is transmitting, the Field Intrinsically Safe Concept can only function when there is no energy feed into the network.
Finally, care should be taken that each terminal unit uses a minimum current. The intrinsic safety of the fieldbus components is not assured unless each terminal unit has a specified consumption value.