1、- - - SD.EEMUA PUB NO LhS-ENGL 1997 E fj7bb7311 0002082 5fli I THE ENGINEERING EQUIPMENT AND MATERIALS USERS ASSOCIATION A GUIDE TO FIELDBUS APPLICATION for the PROCESS INDUSTRY PUBLICATION No 189 : 1997 I EEMUAI COPYRIGHT Engineering Equipment and Materials Users AssociationLicensed by Information
2、Handling ServicesTHE ENGINEERING EQUIPMENT AND MATERIALS USERS ASSOCIATION A GUIDE TO FIELDBUS APPLICATION for the PROCESS INDUSTRY PUBLICATION No 189 : 1997 Copyright o 1997 The Engineering Equipment and Materials Users Association ISBN O 85931 066 3 45 Beech Street LONDON EC2Y SAD Telephone: 0171-
3、628 7878 Fax: 0171-628 7862 1 EEMUA e-mail saleseemua.co.uk website www.eemua.co.uk COPYRIGHT Engineering Equipment and Materials Users AssociationLicensed by Information Handling ServicesTHE ENGINEERING EQUIPMENT AND MATERIALS USERS ASSOCIATION The Engineering Equipment and Materials Users Associat
4、ion-EEMUA-was formed in 1983 by the Amalgamation of the Oil Companies Materials ssociation (OCMA) and the Engineering Equipment Users Association (EEUA). It is an organisation of substantial purchasers and users of engineering products, whose members include leading national and multi-national compa
5、nies in the petroleum, gas, chemical and energy industries. A list of Full and Associate Members (the latter being limited to membership of three technical committees) is given below. EEMUA is concerned with the design, installation, operation and maintenance of the engineering plant used by members
6、 in pursuing their business activities. The Association aims to reduce members costs by providing the opportunity for them to share resources and expertise in order to keep abreast of technological developments and improve the effectiveness and efficiency of their engineering activities. EEMUA suppo
7、rts the British Standards Institution, works with other institutions, associations, government departments, regulatory authorities and the Confederation of British Industry, and is also actively involved with other standards-making bodies, both national and international, such as the American Petrol
8、eum Institute. Work, which is carried out in-house by members alone or with the help of other organisations, may lead to the production of Association publications. These are prepared primarily for members use, but are usually offered for sale and thus for more general use. Such publications may als
9、o be submitted, normally through the British Standards institution, as bases for appropriate national, European or international standards. A list of current EEMUA Publications which may be purchased from the Association is given at the end of this document. Full Members Associate Members Associated
10、 Octel BG BP Ammo Caltex Petroleum Conoco Dow Corning Eastern Generation EssolExxonMobil Eutech Foster Wheeler Energy Lindsey Oil Refinery National Power PowerGen Shell AstraZeneca BASF D a low speed bus at 31.25 Kbits/s and two high speed buses at lMbits/s and 2.5 Mbits/s. Most of the contents of t
11、his document are directed at the design considerations for the low speed bus. Only the 31.25 Kbits/s allows for bus power and Intrinsic safety but for pragmatic reasons will be non- redundant. 6 COPYRIGHT Engineering Equipment and Materials Users AssociationLicensed by Information Handling Services
12、STD-EEMUA PUB NO 189-ENGL 1997 D 57bb73q 0002093 38T D Before starting to design a Fieldbus installation some basic philosophies have to be agreed. An overall Control System philosophy should be prepared to identify the basic requirements for reliability, operator interface, higher level systems, pr
13、otection systems, etc. For Fieldbus based systems the following items need to be considered; O Bus segment topology - A statement is required on the principles to be used in running the field cabling. This should include the type of cable to be used, basic rules on the running of trunks and spurs, s
14、tar connections, etc. including distance limitations. It should also include guidance on the level of security required to cover the various possible power supply failures. 0 Bus segment connections - guidelines are required on the number and types of equipment that can be connected to each bus segm
15、ent taking into consideration physical constraints, the possibility of bus segment failure and the need for future expansion. Also required is guidance on how to connect simple instruments such as thermocouples or switches and a policy regarding the application of multivariable instruments. O Config
16、uration - Basic rules are required on where to locate the control algorithms and on the options for algorithm configuration. The same is true of alarms. Any fast loop or alarm Sequence of Event requirements should be identified. and a change control procedure developed. The tools and preferred metho
17、d of configuration need to be identified 0 Network - The overall network performance requires consideration and the need, if any, for function block scheduling identified 0 Maintenance- A maintenance philosophy should be prepared to identify the preferred method of maintenance and what tools are req
18、uired. 5.3 Interoperability Fieldbus based devices can be specified with various levels of interoperability. The levels can be summarised as; Not-interoperable - A device that uses the communication protocol but has manufacturer specific Function Blocks and device parameters which have not been disc
19、losed. e Limited interoperability - as above but where some, but not all, of the device parameters have been disclosed. 0 Function block interoperable - The manufacturer has specified function blocks as per the specification and disclosed manufacturer specific device parameters 7 COPYRIGHT Engineeri
20、ng Equipment and Materials Users AssociationLicensed by Information Handling ServicesSTD-EEMUA PUB NO 189-ENGL 1997 57bb734 0002094 2Lb Function block interoperable - The manufacturer has specified function blocks as per the specification and disclosed manufacturer specific device parameters o Fully
21、 interoperable - The manufacturer has specified Function Blocks and followed the Device Profile as per the User Layer specification. Any manufacturer specific device parameters have been disclosed. These levels are based on the Fieldbus Foundations specrJications and difler from the those which are
22、being prepared by IEC TC65C Working Group 7. The spec$cations for the User Layer are based on Function Blocks and Device Profiles which set out a basic set of device parameters. Manufacturers can add their own device parameters. These manufacturer specijc parameters can then be disclosed by deliveri
23、ng the Device Description to the Foundation. 8 COPYRIGHT Engineering Equipment and Materials Users AssociationLicensed by Information Handling Services5.4 Failure Modes The Fieldbus Foundation communication protocol has been designed to be deterministic and very robust. Basically the communications
24、will work and a message will arrive correctly or it will not work. The possibility for degraded or erroneous messages being acted on by a device are minimal. The reliability of the bus segment as part of a control or information system will depend on the reliability of the connected devices. A list
25、ofpossible failures and their impact is included in the discussion in Appendix 2. The lower speed bus cannot support redundancy, the higher speeds can. The User should consider redundant bus segmenthost system interface cards where multiple bus segments are installed on a single interface card givin
26、g rise to the possibility of a common mode failure which could fail several bus segments at the same time. The most likely cause of a fatal failure of the bus is through power supply problems. Loss of power supply or any fault on the bus that draws the bus voltage below the minimum 9 volt threshold
27、will stop communications. A total loss ofpower should cause any actuators to move to apreconfgured desiredposition e.g. fail-safe. A fault where the current is drained such as in a partial short circuit and the bus voltage falls below the threshold may not have the same efsect. This may leave the ac
28、tuator in an indeterminate state. It is recommended to configure any final element in a loop to move to the desired safe position on loss of communications. 9 COPYRIGHT Engineering Equipment and Materials Users AssociationLicensed by Information Handling Services6. Cabling and Physical Connections 6
29、.1 Low Speed Bus Segment Topology Fieldbus allows the designer to connect instruments in a number of different configurations. The three basic choices are the “trunk with spurs“, daisy chain (basically a trunk without the spurs) and a tree and branch arrangement known as the “chickens foot“. However
30、 it is possible to combine the different approaches on the same bus segment so long as some of the basic rules regarding number of connections and cable lengths are met (see Appendix I). The attraction of the “Trunk with Spurs“ (and daisy chain) approach is that it will be possible to minimise the c
31、abling requirement. The disadvantages are:- o The requirement to install spur “couplers“ boxes on the trunk Problems associated with connecting a new instrument to the trunk on- Design engineering time associated with determining the optimum o line. trunk routing. For the above reasons the trunk and
32、 spur approach will be attractive to suppliers of “packaged“ iype equipment e.g. large machines, process dryers, etc., where they provide multiple units to a standard design and the same, or similar, cable layout could be used several times. In this situation the design effort required to optimise t
33、he cable layout would be worthwhile. Also the need to install additional instruments on these types of unit is small. In general process plant applications the preferred method is the Chickens Foot. The designer will run a cable fiom the central control equipment to a junction box in the field. From
34、 this box individual spurs will be run to the field devices. The attractions of this approach are:- * Cabling design is similar to traditional methods. Provision can be made in the junction box for adding future instruments. 10 COPYRIGHT Engineering Equipment and Materials Users AssociationLicensed
35、by Information Handling Servicesto individual routing where cable support (e.g. tray) and installation labour costs would be increased. 6.2 Cable Selection Low speed Fieldbus does not require special communication grade cable. The standard was specified to work on new and existing cable installation
36、s. The quality of the cable impacts on the maximum length over which the communications can work reliably. To achieve good performance over reasonable distances requires the cable to meet certain criteria. The optimal cable is given in the 1 158-2 (see Appendix 1) and this cable is recommended for n
37、ew installations. The outer construction should be designed to meet the Users normal requirements for safety and durability (e.g. armoured, etc.) A number of manufacturers have designed cable specifically for Fieldbus communications. These cables tend to have lower signal attenuation than standard s
38、pecijkations. Fieldbus may be run in multicore cables with other types of 24 volt signals and other protocols such as HART, although it is advisable to screen each pair(there may be interference with the HART signal $you don 0. Fieldbus can deliver DC power and communications on the same pair of wir
39、es and this is expected to be the most common approach for instruments such as standard process transmitters. The individual cores need to be colour coded for polarity. Some field devices may require a separate power supply e.g. a Coriolis meter or process analyser, and a four wire connection will b
40、e required. It is permissible to run both the power and the communication on different pairs in the same cable. 6.3 Field Terminal Boxes Field termination boxes should meet the normal requirements for weatherproofing and any hazardous area certification. The User should consider his maintenance prac
41、tices when deciding where to locate the boxes as it is possible that there may be an increased need to enter the box due to Fieldbus. Boxes may be used for single or multiple bus segments. Where multiple bus segments are installed in a box, the terminal strips associated with any single bus segment
42、should be physically segregated from other the bus segments. It is recommended that terminal strips are fitted with some form of isolator to enable the power to be disconnected for individual field devices. 11 COPYRIGHT Engineering Equipment and Materials Users AssociationLicensed by Information Han
43、dling ServicesChickens Foot Junction Box 6.4 Power Supplies Power supplies must meet the criteria and performance specified in IEC 1158- 2. The low power signalling option is preferred. Power is delivered at a nominal 24V and should be available to any device on the bus at a minimal value of 9V (wit
44、h a maximum value of 32 volts). Power is polarised so the cables and terminals should be suitably marked. The end User must define his requirements for the security of the power supply. The power supply may be connected anywhere on a bus segment, however in practice it will most probably be supplied
45、 as an integral element of the host control system manufacturer s Fieldbus interface card arrangement but this may not be always the case. Where Intrinsic Safety barriers are used, the power supplies must be matched with the barrier type. The individual bus segment power supplies should be protected
46、 Tom overcurrent due to faults on the bus segment cable or devices. A current limiting arrangement is preferred to fuses as they are more tolerant to temporary faults such as may occur when work is being done. Power supply type faults on a bus segment should not be able to cause failures of other bu
47、s segments. 6.5 Earthing Fieldbus conductors are non-earthed and electrically isolated from the connected devices and power supply. Earthing requirements for individual devices, cable shields, armouring, etc., should meet the Users normal requirements and take into account any requirements to compiy
48、 with EMC regulations and protection against 12 COPYRIGHT Engineering Equipment and Materials Users AssociationLicensed by Information Handling Serviceslightning. It is recommended that cable shields are earthed at one point only. Earthing shields at each end may introduce circulating currents into
49、the shield that may effect the communications. 6.6 Hazardous Areas Fieldbus installations must be properly certified for use in hazardous areas in respect of zone, gas group and temperature. The type of hazardous area protection adopted is a matter of policy for the user. All the currently recognised methods can be used with the low speed Fieldbus. Applying Isprotection to bus segment networks requires more care due to multiple devices being protected through a single barrier. The Fieldbus Foundation has prepared an application note on “Intrinsically Safe Fieldbus Systems“ whi
