Fieldbus 1 FISCO

Fieldbus Certified Transmitter : Intrinsically safe IIC/Group A T4 Ui : 30V Ii : 100mA Ci : 0.01  F Li : 100  H C c : 0.12  F L c : 4.1mH SYSTEM : IIC/Group A T4 Certified IS interface : Intrinsically safe IIC/Group A U o : 28V I o : 93mA C o : 0.13  F L o : 4.2mH Safety analysis for conventional intrinsically safe instrument loop using the “Entity Concept” Intrinsic Safety Interface Centralised control equipment IS certified device Hazardous areaSafe area IEC 60079/14 : calculate cable parameters compare safety descriptions prepare System Descriptive document

Fieldbus Fieldbus network Safety analysis for conventional intrinsically safe instrument loop using the Entity Concept Intrinsic Safety Interface Centralised control equipment IS certified device Hazardous areaSafe area Certificate for each field device required C:cable = 0.12  F L:cable = 4.1mH Certified IS interface : Intrinsically safe IIC/Group A U o : 28V I o : 93mA C o : 0.13  F L o : 4.2mH Re-calculate if any subsequent modifications

Fieldbus 4 l FF-816 Physical Layer Profile Specification l for hazardous area devices l recommends minimum input l voltage l current & l power levels l maximum l input capacitance & l input inductance l Bus interface output parameters l Field device input parameters

Fieldbus 5 Fieldbus Intrinsically Safe Concept (FISCO) l PTB, the German Test Authority, in collaboration with German industry, examined the intrinsically safe needs of the kbit/s physical layer of Fieldbus and developed an approach which is applicable to IEC l the physical layer employed by both Profibus ‘PA’ & Foundation Fieldbus ‘H1’ systems l A PTB report dated August 1994 provided details of the experimental evidence, from which the IEC standard has emerged l The resulting document covers all aspects of a low frequency Fieldbus system l allows a system to be built with only a minimum analysis of the safety requirements l allows very simple documentation

Fieldbus 6 The FISCO model published in 1994 The FISCO model published in 1994 n IEC defines the FISCO model “Fieldbus Intrinsically Safe Concept” provides clear guidelines for the design & installation of fieldbus networks in explosion protected environments Foundation Fieldbus H1 & Profibus PA Fieldbus network Tree Daisy-chain Spur Host interface

Fieldbus 7 l The experimental work covered a defined range of cable parameters, circuit voltage & current; l hence the permitted cable parameters in a FISCO IS circuit are limited to : These limits are not difficult to achieve, since a typical Fieldbus trunk cable has parameters of : 50  /km, 0,8 mH/km & 120 nF/km l The length of the trunk is usually determined by the operational requirements. ParameterValue Loop resistance15 ohm to 150 ohm / km Loop inductance0.4 mH to 1 mH / km Capacitance80 nF to 200 nF / km Max length of each spur cable30 m in IIC & IIB Max length of each trunk cable1 km in IIC & 5 km in IIB Table 1 - FISCO cable parameters Fieldbus Intrinsically Safe Concept (FISCO)

Fieldbus 8 Resistive V I l The original Foundation Fieldbus specification (FF-816; IEC ) was for a ‘ia IIC’ resistive power supply, which suffers from very restrictive voltage & current Fieldbus Intrinsically Safe Concept (FISCO) MTL5053non-FISCO EEx II (1) GD EEx [ia] IIC [-20 O C to +60 O C] 80 mA 18.4V

Fieldbus 9 l The FISCO standard examined the ignition capability of constant current power supplies l it proposed acceptable levels of power for supplies with a ‘trapezoidal’ characteristic, as opposed to those with a falling, resistor-limited characteristic. l This permits a greater useable power for the Fieldbus trunk; l particularly if the less sensitive gas group IIB (Ethylene) is declared Fieldbus Intrinsically Safe Concept (FISCO) Trapezoidal Resistive V I l by use of a constant current power supply, its application into Zone 0 is not allowed

Fieldbus 10 FISCO in North America l The use of active semiconductors to limit the current l results in power supplies being restricted to ‘ib’ level of protection in accordance with IEC & CENELEC apparatus standards l ie, system is not directly applicable to Zone 0 applications l However, the design of MTL power supplies satisfies the North American requirement for intrinsically safe apparatus for Divisions 1 & 2

Fieldbus 11 The FISCO model l Power Supply : constant current control : l trapezoidal fall-off l V max up to 17.5 volts l IIC IIB l Imax 183 mA 380 mA l Pmax 2.56 Watts5.32 Watts l Safety Factor of 1.5 has been incorporated Trapezoidal Resistive V I

Fieldbus Output Voltage (V) Short Circuit Current (mA) Safety Limits IIC IIB ModelApparatusSafety DescriptionUseable Number Class Output Uo Io PoVmA 9121-IS IIC IS IIB FISCO defined safety limits 9122-IS X X X X Operating points 9121-IS X X Nominal Min. Safety

Fieldbus 13 Comparison of Safety Parameters FOUNDATION Fieldbus FISCO Parameters

Fieldbus 14 l The FISCO model is based on the following mandate : l Each segment has only one source of power & no additional power is fed to the bus l the field devices act as passive current sinks l Passive line termination is in place at both ends of the main bus line l Line length limited to : 1 Km in IIC : 1900 m in IIB (FF-816 limit) l Spur length limited to : 30 metres (60 metres proposed) l Each device : capacitance & inductance limited to Ci < 5 nF, Li < 10 uH l Linear, tree, & star networks are permitted The FISCO model

Fieldbus 15 The Procedure for FISCO implementation The Procedure for FISCO implementation l Select “FISCO approved field devices” (for H1 or PA) l Apparatus Certificate to state suitability for FISCO system l The certification of FISCO field devices will define : l capacitance [ Ci ] < 5nF l inductance [ Li ] < 10H l may have any temperature classification - but the majority will be T4 (135 O C) l IIC ; with input parameters of : l voltage [ Ui ] 17.5V; l current [ Ii ] 380mA; l power [ Pi ] 5.32W; l Quite a demanding spec on instrumentation

Fieldbus 16 The Procedure for FISCO implementation The Procedure for FISCO implementation l Select “FISCO approved field devices” (for H1 or PA) l Apparatus Certificate to state suitability for FISCO system l The bus cable must have the following properties : l R = 15…150 ohms/km l L = 0.4…1 mH/km l C = 80…200 nF/km l Ensure termination is fitted l 90 to 102 ohms in series with 0 to 2.2 uF l No calculation of C & L cable parameters necessary

Fieldbus 17 l Major benefits of the FISCO system are : Documentation & Inspection l no detailed analysis is necessary to ensure the safety of the system l additions do not require reassessment of the whole system l the documentation is only a list of the connected apparatus l electronic format sufficient l can simply cross-refer to the certification documents of the apparatus l the inspection procedure is that of ensuring the system is unchanged & undamaged l The reader is referred to Application Note AN9026 : Section 1.7 : Documentation & Inspection Section 8 : Certification & Safety; Documentation of FISCO Systems

Fieldbus 18 FISCO - Detailed Design l In practice most instruments take less than 20 mA thus permitting an increase in population l The calculation of how many field devices can be powered on a bus is a simple application of ‘Ohms Law’ l take the current consumption of each field device, l deduce the voltage drop in the trunk cable, l remembering that the fielddevices require 9V to operate. l If the assumption is : l all field devices take 20mA l all are located at the remote end of the IS trunk l typically, the number of devices which can be powered from a IIC power supply is 5 at the end of a 600m trunk l The corresponding IIB power supply will supply 13 devices at the end of a 300m trunk l demonstrating the desirability of a IIB gas classification where possible

Fieldbus 19 Terminators R L C R L C R L C Terminator 100  1  F l FISCO power supplies typically contain a permanently connected terminator which defines one end of the IS trunk l The field end of the IS trunk also requires to be terminated l Typically, the terminator is FISCO approved, and hence can be used without any further consideration of the system safety l Terminators are used to present a 100  impedance to each end of the trunk l to match the cable characteristic impedance l to avoid reflections l typical certification : l ATEX Category II 1 l CENELEC EEx ia IIC T4 FBT1-IS

Fieldbus 20 Zone 1 / Div1 Hazardous Area Host T DC supply LNELNE TT Safe Area T l The incoming power supply is converted to an intrinsically safe supply to feed the IS trunk l The Fieldbus signal, which is superimposed on the IS voltage, is fed via the interface device to & from the field devices Power conditioner Typical application

Fieldbus 21 Note : 3-port isolation l A typical power supply offers isolation between : l the power source l the safe area bus l the IS bus & its terminator/s l Optionally acts as a repeater as well as a power source l Includes some diagnostic capability. l These features are not FISCO requirements but are operationally desirable.

Fieldbus 22 è FISCO serves all gas groups & hazardous areas è The number of field devices that can be connected to a fieldbus segment will be limited only by : è the power available è the resistivity of the cable connection è The segment can be extended without the need for new calculations (within the boundaries of the FISCO model ) è FISCO devices from different suppliers can be interchanged without any re-calculation è No System certification required Summary

Fieldbus kbit/s Tree Daisy-chain Spur Summary FISCO Application FISCO Application Entity Approach Entity Approach Line length limit : 1 Km in IIC : 1.9 Km in IIB (FF-816) Max spur length : 30 m ( 60 m proposed ) No cable parameter considerations required Simple interchange of devices Line length limit : 1 Km in IIC : 1.9 Km in IIB (FF-816) Max spur length : 30 m ( 60 m proposed ) No cable parameter considerations required Simple interchange of devices Line length limit all gases : 1.9 Km (FF-816) Max spur length : 120 m Full calculation of safety parameters Line length limit all gases : 1.9 Km (FF-816) Max spur length : 120 m Full calculation of safety parameters