[FUN] IS vs Explosion Proof vs FISCO

[Stephen Mitschke]

If you're looking for detailed technical information on FISCO, the MTLApplication Note AN9026 provides a good introduction.http://www.process-io.com/Download.nsf/ac2042e45d1348cd002568ab0063c3f3/56a832c503efbee980256c53004d873f?OpenDocumentThe big advantage of FISCO, is it allows an IS hazardous area fieldbus tobe installed in exactly the same way as a general purpose fieldbus. WithFISCO power supplies you can simply calculate maximum cable length from thecable voltage drop. In addition the only certification documentation yourequire is a simple list of the field devices. Exactly as on a safe areaapplication. The complicated voltage drop and cable parameter calculationsrequired for other IS products are not needed.FISCO power supplies typically provide 110mA in Gas Groups A,B (IIC) and250mA in Gas Groups C,D (IIB) more than any other IS fieldbus power supplytoday (the 350mA IS power supply referred to in an earlier e-mail, sharesthis current between two IS trunks). FISCO has gone through the rigorousinternational standard review process, and is now documented in IEC60079-27The FISCO Technical Specification in addition to being a physical layerprofile within FF816. To avoid doing the cable parameter calculations theloop resistance must be between 15 and 150 ohms / km, loop inductance 0.4to 1 mH / km, loop capacitance 80 to 200 nF / km, the maximum spur lengthis 30m and the maximum trunk length is 1 km in IIC or 5 km in IIB. Almostall instrument cables meet these requirements, and if they don't you canstill use a FISCO power supply, you just need to do the calculations.Lots of FISCO certified fieldbus devices are now available. On the recentInfraserv FF interoperability test in Germany, 63% of the 42 differentdevices were FISCO certified when received in Jan 02, and 83% will be FISCOcertified by the end of 2002.Finally, our experience has been, when commissioning, maintaining orexpanding a fieldbus system, live connection/disconnection of fieldbusdevices is required and intrinsic safety allows this to be done without agas clearance certificate. The only other hazardous area protectiontechnique allowing live connection/disconnection is non-incendive fieldwiring in Division/Zone 2, but for this you can use FNICO FieldbusNon-Incendive COncept, but that will require another e-mail.(See attached file: AN9026-1.pdf)Roger Highton MTL Instruments

[Stephen Mitschke]

Simple correction:The Hawke systems puts 350mA into one or two trunks, the choice is left tothe systems designer.Using 2 trunks gains even more freedom from Ohm's Law, since the current issplit into 2 legs which also reduces voltage drop at source.All we have done is provide 2 output channels for the price of one; anysupplier can do the same. It just so happens that we had the space and theforethought to do so.However, if anyone wishes to run the segment as one wire-pair, the full350mA is still available into that segment. The choice is the cost ofanother wire-pair vs the inability to drive as many devices as needed persegment.Naturally, FISCO devices can also be used, you just won't have the FISCOoperational restrictions!Mike O'NeillHawke Fieldbus