FISCO and CSA

[FFuser]

Does Fisco comply to CSA standards? Or in other words if we design a network to FISCO standards does it meet section 18 of the code for a class 1 zone 2 enviroment.

[Mike ONeill]

As far as I am aware, practically all suppliers of IS fieldbus interfaces (power supplies / barriers) have CSA approval and FISCO is an accepted extension to the IS standards for CSA.

However, if what you really want is to use IS fieldbus devices in a CSA-approved manner, then don’t rule out the other possibilities: fieldbarriers & split-architecture. The complete FISCO system (‘pure’ FISCO = FISCO power supply, FISCO cable, FISCO device & FISCO screwdriver) has, by its very design & approval criteria, some restrictions which may be troublesome. For example, a ‘pure’ FISCO system is restricted to 1000m total cable/60m spurs and 110mA* in IIC, and only relaxes to 260mA* in IIB (*manufacturer-specific values). Most importantly of all for most users, the overall availability of ‘pure’ FISCO segments is limited by the very complexity of the internal power supply design (ask your supplier for data). There is no redundancy between FISCO power supplies, though I believe one supplier is concocting a scheme whereby two complex switch mode FISCO power supplies have some sort of hot-switching arrangement on detection of failure of one unit, to try to overcome that restriction.

Fieldbarriers allow you to use non-intrinsically safe power supplies of whatever size you need to drive those units in the field, and each fieldbarrier can support 4 or 8 intrinsically-safe spurs (FISCO or Entity, any mix). The power supplies can be redundant pairs if required, and the overall segment does not have the FISCO cable restrictions. However, the trunk is not IS and has to be protected in some other manner suitable for the intended Zone of installation. Fieldbarrier segments are available from MooreHawke, Turck, P+F and Stahl.

If a fully-IS solution is required, with the highest availability and the connection of any IS device (FISCO and Entity), then split-architecture schemes should be worth a look. The split-architecture design provided by my own company has CSA approval and allows a redundant hot-swappable load-sharing DC power system with passive conditioning, making the segment availability extremely high. (MTBF of the Rack with dual DC supplies is quoted as 5188 years, and the individual Trunk Isolator Module as 1248 years). Since it is not a FISCO power supply, there are no restrictions on the cable length for trunk or spur other than Ohms law. The split-architecture system allows connection of individual FISCO and Entity devices per spur and because each spur is considered a separate IS circuit (similar to a fieldbarrier), entity parameters need only be considered once for the whole installation, assuming that you are going to use a common cable type on the plant. There is a restriction – the trunk and the field device coupler is only approved to IIB while the spurs & hence devices are IIC approved. This may cause you a problem if you have that rare thing: a plant with a real IIC hazard more than 100m across!