Technical Overview
Contents
1. Fieldbus Device 2 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Figure 31 shows an example of how common Function Block variables map into the views Only a partial listing of the block parameters is shown in the example e VIEW_1 Operation Dynamic Information required by a plant operator to run the process Technology 3 3 4 Fieldbus Device Definition The function of a fieldbus device is determined by the arrangement and interconnection of blocks Figure 32 The device functions are made visible to the field bus communication system through the User Application Virtual Field Device VFD discussed ear e VIEW_2 Operation Static Information which lier may need to be read once and then displayed along with the dynamic data The header of the User Application object dictionary points to a Directory which is always the first entry in the function block application The Directory pro vides the starting indexes of all of the other entries used in the Function Block application Figure 33 e VIEW_3 All Dynamic Information which is changing and may need to be referenced in a detailed display e VIEW_4 Other Static Configuration and mainte nance information Function Block Application Resource Block Sensor Transducer Function 4 Block 1 Block 1 Links Dynamic lA PID AO Data Trend Alarms Static Fieldbus ow R Diagnostics Detail Display Display2. All rights reserved Wiring was configured by connecting the fieldbus devices to one of two terminal panels in a junction box located by the process equipment Two wire pairs one pair for each terminal panel were used to connect the fieldbuses to the control room The total condensate level of the system is controlled by selecting a preferred setpoint on the level PID LIC 101 which ts located in the level transmitter The level PID is used as the primary loop cascaded to the flow PID FIC 103 located in the valve on the feedwater system The re circulation of condensate from the conden Sate tank to the flash tank is controlled by an addi tional PID loop FIC 202 located in the valve The control strategy for this cascade loop is totally implemented in the transmitters and flow valve as shown in Figure 47 5 2 Installation Startup and Operation Benefits Observed The wire runs from fieldbus devices to the terminal panel averaged 28 metres of new wire for each device while two 185 metres of existing wire runs were used from each of the terminal panels to the control room If standard 4 20 mA analog devices had been used ten new runs of 230 metres 28 metres from the device to the terminal panel plus 185 metres to the equipment room plus 17 metres to the DCS would have been required Savings in installation costs are Summarized in the following table Wiring Technology Wire Length Number of Screw Terminations 4
3. This example states that the items Access specifi example the remote device would use the Create cation and sub index occur in SEQUENCE in the Program Invocation FMS service to change the message program state from Non existent to Idle The Access specification is a CHOICE of using The Start FMS service would be used to change either an index or a name to access a variable the state from Idle to Running and so on The sub index is OPTIONAL It is used only to 3 3 User Application Blocks select an individual element of an array or record variable a FF 890 Function Blocks Part 1 The Fieldbus Foundation has defined a standard User Application based on Blocks Blocks are representations of different types of application functions Figure 28 The numbers in the brackets are the actual encod ing numbers that are used to identify the fields in an encoded message 3 2 3 4 Protocol Behavior The types of blocks used in a User Application are Certain types of objects have special behavioral described in Figure 29 rules that are described by the FMS specification For example the simplified behavior of a Program 3 3 1 Resource Block Invocation object is shown in Figure 27 The Resource Block describes characteristics of the fieldbus device such as the device name manufac turer and serial number There is only one resource block in a device Non DELETE USER USER existent l APPLICATION APPLICATION CREATE Unrunnable R
4. alarm acknowledge and device upload and download 3 2 2 2 Report Distribution VCR Type The Report Distribution VCR Type is used for queued unscheduled user initiated one to many communications When a device with an event or a trend report receives a Pass Token PT from the LAS it sends its message to a group address defined for its VCR Devices that are configured to listen on that VCR will receive the report The Report Distribution VCR Type is typically used by fieldbus devices to send alarm notifications to the operator consoles 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology 3 2 2 3 Publisher Subscriber VCR Type The Publisher Subscriber VCR Type is used for buffered one to many communications Buffered means that only the latest version of the data is maintained within the network New data completely overwrites previous data When a device receives the Compel Data CD the device will Publish or broadcast its message to all devices on the fieldbus Devices that wish to receive the Published message are called Subscribers The CD may be scheduled in the LAS or it may be sent by Subscribers on an unscheduled basis An attribute of the VCR indicates which method is used The Publisher Subscriber VCR Type is used by the field devices for cyclic scheduled publishing of User Application function block input and outputs such as process variable PV
5. Any host using the Device Description Services DDS interpreter will be able to interoperate with all parameters that have been defined in the device by reading the device s DD 4 SYSTEM CONFIGURATION Fieldbus system configuration consists of two phases 1 System Design and 2 Device Configuration 4 1 System Design The system design for fieldbus based systems is very similar to today s Distributed Control Systems DCS design with the following differences Control Room Console 31 25 kbit s Fieldbus 2 Figure 43 The first difference is in the physical wiring due to the change from 4 20 mA analog point to point wiring to a digital bus wiring where many devices can be connected to one wire Each device on the fieldbus must have a unique physical device tag and a corresponding network address The second difference is the ability to distribute some of the control and input output I O sub sys tem functions from the control system to the field bus devices This may reduce the number of rack mounted controllers and remote mounted I O equip ment needed for the system design Figure 43 4 2 Device Configuration After the system design is completed and the instruments have been selected the device configu ration is performed by connecting Function Block inputs and outputs together in each device as required by the control strategy Figure 44 After all of the function block connections and other configura
6. Device Description Language Specification 31 25 kbit s Communication Profile Physical Layer Proportional Integral Derivative Probe Node Pass Token System Management System Management Information Base Simple Network Managemant Protocol Simple Network Time Protocol PHY SMIB SNMP kbit s LAS Mbit s OD OSI J PDU P PID PN SMIB SNMP SNTP TCP IP Transport Control Protocol Internet Protocol Time Distribution TD Virtual Field Device Virtual Communication Relationship 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved
7. Management ServiceS 0 eee eens 12 3 2 3 2 2 Object Dictionary ServiceS 0 ee eee eens 12 3 2 3 2 3 Variable Access ServiceS daria A EA A Shed a 12 zi 4 EVEN SCIVICES aria a Aaa 12 3 2 3 2 5 Upload Download Services o ooooooorrnrnr eee tee ns 13 3 2 3 2 6 Program Invocation ServiceS 1 0 ce eee eee ete n eee 13 323 3 Message POLMAMING ace ELA A bee Sd a eee Ee eRe eae ek Es 13 3234 PTOWOCOlDCNAVIOl 262444560 55 A tae eee eta ta II dd ees 14 3 3 User Application Blocks 0 0 cc ee eee een eens 14 Bo RESOU E BOCK da aac ails Sane a Ada alee 14 Se FUNC ON Bs OCI tothe gp toad ot ttre etna die dtu ate E O eon ee 15 o o a 140 505 Fete eds do hes eee bee 4 b bre ae ae ae ee ed ee 15 3 3 4 Fieldbus Device Definition 0 0 cc ee eee eee eens 16 3 4 System Management 17 324 1 FUNCHON BIOCK SCMhCQUIING 3 4 83 s 2F cae pay ado ae aks aes ee eed bed 17 3411 Application COCK DISTIDUION lt td eee bd ae ote ares we ieee eho eka ead 18 3 4 1 2 Device Address Assignment 0 0 cee ee eee A 18 Soleo PING le oy CIVICE a 44 4 4 i wren BRA DAS doy sew rae Venlo eae ae a tee he a 19 3 5 Device Descriptions a IE O ee be ee ee Ge we ARAS 19 3 5 1 Device Description Tokenizer 0 0 ee eee eet eet tenes 19 3 5 2 Device Description Services DDS 10 eee eens 20 3 5 3 Device Description Hierarchy 0 cc ee eee eee eee ene 21 320 4 INteroperabll liada oe a RO AR CR A whee eee eee Ee 22
8. PID control may be performed by the field device through the use of Function Blocks Figure 6 The consistent block oriented design of function blocks allows distribution of functions in field devices from different manufacturers in an integrated and seamless manner Distribution of control into the field devices can reduce the amount of I O and control equipment needed including card files cabinets and power supplies 1 1 4 Wiring Savings The fieldbus allows many devices to connect to a single wire pair This results in less wire fewer intrinsic safety barriers and fewer marshaling cabinets Figure 7 Control System rs _ Control System Network Network Controller Controller Remote Input Output Subsystem Fieldbus Traditional 4 20 mA View Stops at I O Subsystem Fieldbus View Extends into Instrument Figure 5 Control System Network Control System Network pola Fieldbus Wiring One l S Barrier One Wire Traditional 4 20 mA Wiring for One I S Barrier One Wire Many Devices for Each Device Figure 7 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved 2 0 WHAT IS THE FIELDBUS FOUNDATION Driven by their customers needs process contro and manufacturing automation companies formed the Fieldbus Foundation to complete development of a single open international and interoperable fieldbus The Fieldbus Foundation is an independent not for profit
9. Physical Layer 2 the Communication Stack and 3 the User Application The Open Systems Interconnect OSI layered communication model is used to model these components Figure 9 The Physical Layer is OSI layer 1 The Data Link Layer DLL is OSI layer 2 The Fieldbus Message Specification FMS is OSI layer 7 The Communi cation Stack is comprised of layers 2 and 7 in the OSI model The fieldbus does not use OSI layers 3 4 5 and 6 The Fieldbus Access Sublayer FAS maps the FMS onto the DLL The User Application is not defined by the OSI model The Fieldbus Foundation has specified a User Application model Fieldbus Model USER USER APPLICATION APPLICATION FIELDBUS MESSAGE SPECIFICATION FIELDBUS ACCESS SUBLAYER OSI Model APPLICATION LAYER The user application is not defined by the OSI Model COMMUNICATION STACK PHYSICAL LAYER Figure 9 Technology Each layer in the communication system is respon sible for a portion of the message that is transmitted on the fieldbus The numbers below show the approximate number of eight bit octets used for each layer to transfer the USER data Figure 10 3 1 Physical Layer 31 25 kbit s ISA 50 02 1992 ISA Physical Layer Standard IEC 61158 2 1993 International Physical Layer Standard tn FF 816 31 25 kbit s Physical Layer Profile Specification tn FF 818 31 25 kbit s Fiber Optic Physical Layer Profile The Physical Layer is
10. addresses System Management asks the device for its physical device tag System Management uses the physical device tag to look up the new network address in a configuration table System Management then sends a special set address message to the device which forces the device to move to the new network address e The sequence is repeated for all devices that enter the network at a default address 3 4 1 3 Find Tag Service For the convenience of host systems and portable maintenance devices System Management supports a service for finding devices or variables by a tag search The find tag query message is broadcast to all fieldbus devices Upon receipt of the message each device searches its Virtual Field Devices VFD for the requested tag and returns complete path information if the tag is found including the network address VFD number virtual communication relationship VCR index and object dictionary OD index Once the path is known the host or maintenance device can access the data for the tag 3 5 Device Descriptions A critical characteristic required of fieldbus devices is interoperability To achieve interoperability ge Virtual Field Device Object Description Pointer to Device Description s Extended Descriptions Associated with the Data Label of the parameter Engineering units How many decimal points to display Help text Parameter relationships Calibration and diagnos
11. and primary output OUT on the fieldbus 3 2 2 4 Summary of VCR Types Figure 22 3 2 3 Fieldbus Message Specification FMS La FF 870 Fieldbus Message Specification Fieldbus Message Specification FMS services allow user applications to send messages to each other across the fieldbus using a standard set of message formats FIELDBUS ACCESS SUBLAYER SERVICES Client Server Report Distribution Publisher Subscriber VCR Type VCR Type VCR Type Used for Used for Used for Operator Messages Event Notification Publishing Data and Setpoint changes Trend Reports Mode changes Tuning changes Upload Download Alarm Management Access display views Remote diagnostics DATA LINK LAYER SERVICES Figure 22 Send process alarms Send transmitter PV to operator consoles to PID control block and operator console Send trend reports to data historians FMS describes the communication services mes sage formats and protocol behavior needed to build messages for the User Application Figure 23 Data that is communicated over the fieldbus is described by an object description Object descriptions are collected together in a structure called an object dictionary OD Figure 24 The object description is identified by its index in the OD Index 0 called the object dictionary head er provides a description of the dictionary itself and defines the first index for the object descriptions of the User Applic
12. end delimiter Figure 13 USER APPLICATION Example of voltage mode signaling Fieldbus Messages COMMUNICATION STACK PHYSICAL LAYER Fieldbus Media Wire Figure 11 1 Bit Time The preamble is used by the receiver to synchronize its internal clock with the incoming fieldbus signal Special N and N codes are in the start delimiter and end delimiter Note that the N and N signals do not transition in the middle of a bit time The receiver uses the start delimiter to find the beginning of a fieldbus message After it finds the start delim iter the receiver accepts data until the end delimiter is received 3 1 1 31 25 kbit s Fieldbus Signaling The transmitting device delivers 10 mA at 31 25 kbit s into a 50 ohm equivalent load to create a 1 0 volt peak to peak voltage modulated on top of the direct current DC supply voltage PREAMBLE START DELIMITER MANCHESTER BIPHASE L ENCODING END DELIMITER Figure 12 Figure 13 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology The DC supply voltage can range from 9 to 32 volts 3 1 2 31 25 kbit s Fieldbus Wiring However for I S applications the allowed power i AG 140 31 25 kbit s Wiring and Installation Guide supply voltage depends on the barrier rating AG 163 31 25 kbit s Intrinsically Safe Systems Figure 14 Application Guide AG 165 Fieldbus Installation and Planning Guide 31 25 kb
13. 20 mA Analog 2300 metres Fieldbus The reduction of interface cards by 50 equip ment cabinet space caused by a reduction in the number of I O interfaces and the elimination of ter mination panels resulted in a 46 reduction in equipment costs Field Test Some applications might specify fewer devices per wire pair than the test system In that case the savings shown in the above table would be pro portionately reduced according to the specific wiring configuration During the checkout phase a reduction in effort to confirm the proper connection of the fieldbus devices was observed One person performed the checkout by using the test tool connected to the fieldbus With conventional 4 20 mA wiring two people would have been required to check out each wire and confirm operation of each transmitter Each transmitter was interrogated and adjusted remotely Device parameters such as the high and low range values were changed without having a technician adjust a potentiometer in the field When a device was disconnected from the fieldbus the disconnection did not affect any other devices remaining on the bus When the device was recon nected the system had no trouble re establishing communication with the device Approximately two person days of labor 25 were saved due to the remote verification of wiring remote device identifi cation and remote device configuration checkout The processing load on the D
14. 6 System Management in the transmitter will cause the Al function block to execute at offset 0 At offset 20 the Link Active Scheduler LAS will issue a Compel Data CD to the Al function block buffer in the transmitter and data in the buffer will be published on the fieldbus At offset 30 System Management in the valve will cause the PID function block to execute followed by execution of the AO function block at offset 50 The pattern exactly repeats itself assuring the integrity of the control loop dynamics Note that during the function block execution the LAS is sending the Pass Token message to all devices so that they can transmit their unscheduled messages such as alarm notifications or operator setpoint changes For this example the only time that the fieldbus can not be used for unscheduled messages is from off set 20 to offset 30 when the Al function block data is being published on the fieldbus 3 4 1 1 Application Clock Distribution The FOUNDATION Fieldbus supports an application clock distribution function The application clock is usually set equal to the local time of day or to Universal Coordinated Time Technology System Management has a time publisher which periodically sends an application clock synchroniza tion message to all fieldbus devices The data link scheduling time is sampled and sent with the appli cation clock message so that the receiving devices can adjust their local application time
15. Between synchronization messages application clock time is independently maintained in each device based on its own internal clock Application Clock synchronization allows the devices to time stamp data throughout the fieldbus network If there are backup application clock publishers on the fieldbus a backup publisher will become active if the currently active time publisher should fail 3 4 1 2 Device Address Assignment Every fieldbus device must have a unique network address and physical device tag for the fieldbus to operate properly To avoid the need for address switches on the instruments assignment of network addresses can be performed automatically by System Management The sequence for assigning a network address to a new device is as follows e A physical device tag is assigned to a new device via a configuration device This can be done off line at a bench or on line through special default network addresses on the fieldbus The start of individual macrocycles is defined as an offset from the absolute link schedule start time Absolute Link Schedule Start Time DL Offset 0 for Al execution Device 1 Macrocycle LAS Macrocycle Unscheduled Communication Permitted Device 2 Macrocycle LAS Schedule Duration Sequence Repeats LAS Schedule Duration Figure 36 O 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology e Using default network
16. CD Compel Data b CD a Fieldbus E Message TELGE BASIC LINK MASTER BASIC BASIC LINK MASTER BASIC J DEVICE DEVICE DEVICE DEVICE DEVICE DEVICE l l l Y Y Figure 18 Publisher Subscriber Subscriber Figure 19 O 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology 3 2 1 3 Unscheduled Communication All of the devices on the fieldbus are given a chance to send unscheduled messages between trans missions of scheduled messages The LAS grants permission to a device to use the fieldbus by issuing a pass token PT message to the device When the device receives the PT It is allowed to send messages until it has finished or until the maximum token hold time has expired whichever is the shorter time Figure 20 3 2 1 4 Link Active Scheduler Operation The following sections describe the overall opera tion of the Link Active Scheduler LAS The algo rithm used by the LAS is shown in Figure 21 3 2 1 4 1 CD Schedule The CD Schedule contains a list of activities that are scheduled to occur on a cyclic basis At pre cisely the scheduled time the LAS sends a Compel Data CD message to a specific data buffer in a fieldbus device The device immediately broadcasts or publishes a message to all devices on the field bus This is the highest priority activity performed by the LAS The remaining operations are per formed between scheduled transfers Unschedule
17. CS controller was reduced because of the PID algorithms which were executing in the fieldbus devices LEVEL FLOW TRANSMITTER TRANSMITTER LT 101 FT 204 Condensate Out Flow OUT BK_CALO BK_CAL IN BK_CAL OUT AO vo 103 Condensate Out Flow Loop BK_CAL IN Condensate Flash Level Figure 47 O 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved High Speed Ethernet 6 HIGH SPEED ETHERNET Since all of the 31 25 kbit s FOUNDATION fieldbus mes sages are communicated on the HSE using standard A Linking Device is used to interconnect 31 25 kbit s Ethernet protocols e g TCP IP SNTP SNMP etc fieldbuses and make them accessible to a High commercial off the shelf HSE equipment such as Speed Ethernet HSE backbone running at 100 Mbit s Switches and Routers are used to create larger net or 1Gbit s Figure 48 The I O Subsystem Interface works Figure 49 Of course all or part of the HSE Shown in the figure allows other networks such as network can be made redundant to achieve the level DeviceNet and Profibus to be mapped into standard fault tolerance needed by the application FOUNDATION fieldbus function blocks The I O Subsystem Interface can be connected to the 31 25 kbit s fieldbus or HSE Automation and Display Devices Automation ane i Soe tar hea Enui Display Systems AP LE AAA MUA A Santilard HSE Linking Device AL ___ O HEE 31 24 kb t s a LO ha Subeysiem pa s
18. ESET nl m Idle i FIELDBUS MESSAGE START KILL SPECIFICATION Running gt FIELDBUS ACCESS SUBLAYER STOP RESUME COMMUNICATION Stopped E STACK DATA LINK LAYER Behavior Rules for the Program Invocation Object PHYSICAL LAYER PHYSICAL LAYER A remote device can control the state of the program in another device on the fieldbus For Figure 27 Figure 28 Resource Block Transducer Function Block Block COMMUNICATION STACK PHYSICAL LAYER Fieldbus Figure 29 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology 3 3 2 Function Block Function Blocks FB provide the control system behavior The input and output parameters of Function Blocks can be linked over the fieldbus The execution of each Function Block is precisely scheduled There can be many function blocks in a single User Application The Fieldbus Foundation has defined sets of stan dard Function Blocks Ten standard Function Blocks for basic control are defined by the xn FF 891 Function Blocks Part 2 specification These blocks are listed below Function Block Name Symbol Analog Input Al Analog Output AO Blas B Control Selector CS Discrete Input DI Discrete Output DO Manual Loader ML Proportional Derivative PD Proportional Integral Derivative PID Ratio RA Nineteen additional standard Funct
19. Fieldbus Foundation dedicated to a single international fieldbus FD 043 Rev 2 0 Technical Overview FOUNDATION fieldbus Compliments of FOUNDATION Fieldbus Technical Overview FD 043 Revision 2 0 This technical overview booklet has been prepared to aid understanding of the technical aspects Of FOUNDATION fieldbus The booklet begins with a brief overview of fieldbus benefits followed by the goals principles and organization of the not for profit Fieldbus Foundation The main portion of the booklet is devoted to the definition and explanation of key technical concepts underpinning FOUNDATION fieldbus technology sincerely hope this information proves useful to you Please contact the Fieldbus Foundation if you need additional information about this exciting new technology David A Glanzer Director of Technology Development For additional information please contact Fieldbus Foundation 9390 Research Boulevard Suite 11 250 Austin TX 78759 USA Voice 512 794 8890 Fax 512 794 8893 Visit our World Wide Web Site http www fieldbus org DISCLAIMER OF WARRANTIES This document is provided on an as is basis and may be subject to future additions modifications or corrections The Fieldbus Foundation hereby disclaims all warranties of any kind express or implied including any warranty of merchantability or fitness for a particular purpose for this document In no event will the Fieldbus F
20. Link Active Scheduler Algorithm Wait Is until it is time to there time to do issue the CD something before next __ Send CD idle messages while waiting CD Compel Data PN Probe Node TD Time Distribution PT Pass Token Issue PN TD or PT Figure 21 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved 3 2 1 4 3 Data Link Time Synchronization The LAS periodically broadcasts a Time Distribution TD message on the fieldbus so that all devices have exactly the same data link time This is impor tant because scheduled communications on the fieldbus and scheduled function block executions in the User Application are based on information obtained from these messages 3 2 1 4 4 Token Passing The LAS sends a Pass Token PT message to all devices in the Live List The device is allowed to transmit unscheduled messages when it receives the PT 3 2 1 4 5 LAS Redundancy A fieldbus may have multiple Link Masters If the current LAS fails one of the Link Masters will become the LAS and the operation of the fieldbus will continue The fieldbus is designed to fail oper ational 3 2 2 Fieldbus Access Sublayer FAS Ln FF 875 Fieldbus Access Sublayer Specification The FAS uses the scheduled and unscheduled fea tures of the Data Link Layer to provide a service for the Fieldbus Message Specification FMS The types of FAS services are described by Virtual Communication Relation
21. SYSTEM CONFIGURATION ovio itra sa I a E eee 22 4 1 System Design sarro FOR ee ee A A A NA AS 22 4 2 Device Configuration ee eee eens 22 FIELD TEST SYSTEM Guiso a eae AE ee eee he AA wk 23 5 1 Test Instrumentation s xiii Ph HEE ee RAM eh ARA a a ee 23 5 2 Installation Startup and Operation Benefits Observed 0 0 eee 24 HIGH SPEED ETHERNET ice ieee A A ae AAA SARA E A 25 REFERENCES 625 save eee eee ei AO Fe a 26 DOCUMENT LIST eras wert ohne ria ii odes Ate de den 26 ACRONYM TABLE asii taria a hn we Ee Re ae aa eae Se ae aes 26 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Introduction 1 0 WHAT IS FOUNDATION FIELDBUS In addition FOUNDATION fieldbus enables FOUNDATION fieldbus is an all digital serial two way e increased capabilities due to full digital communication system running at 31 25 kbit s which communications interconnects field equipment such as sensors actua tors and controllers Fieldbus is a Local Area Network LAN for instruments used in both process and manu e reduced wiring and wire terminations due to multiple devices on one wire facturing automation with built in capability to distribute e increased selection of suppliers due to the control application across the network Figure 1 interoperability The fieldbus environment is the base level group of reduced loading on control room equipment digital networks in the hierarchy of plant
22. Sets View_1 View_2 x View_3 View 4 Operation Operation a a XYZ Block Dynamic R ae All Dynamic Other Static BV X o Sensor SP HI LIMI 2 CAS IN X GAIN X Figure 31 Function Block 2 Transducer Block 2 Figure 32 OD HEADER DIRECTORY RESOURCE BLOCK FUNCTION BLOCKS TRANSDUCER BLOCKS LINK OBJECTS ALERT OBJECTS TREND OBJECTS VIEW OBJECTS Figure 33 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology The VFD object descriptions and their associated data are accessed remotely over the fieldbus net work using Virtual Communication Relationships VCRs as shown below Figure 34 3 4 System Management La FF 800 System Management Specification Function Blocks must execute at precisely defined intervals and in the proper sequence for correct control system operation System management synchronizes execution of the Function Blocks and the communication of function block parameters on the fieldbus System management also handles other important system features such as publication of the time of day to all devices including automatic switchover to a redundant time publisher automatic assignment of device addresses and searching for parameter names or tags on the fieldbus All of the configuration information needed by System Management such as the Function Block schedule is described by object descriptions in the Network and System Management V
23. Tokenizer Tool Figure 38 O 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology The Fieldbus Foundation FF provides DDs for all 3 5 2 Device Description Services DDS standard Function Blocks and Transducer Blocks Device suppliers will typically prepare an incremen un FD 110 DDS User s Guide tal DD which references the Standard DDs Suppliers may also add supplier specific features On the host side library functions called Device such as calibration and diagnostic procedures to Description Services DDS are used to read the their devices These features can also be described device descriptions Figure 40 in the incremental DD Note that DDS reads descriptions not operational The Fieldbus Foundation makes the Standard DDs values The operational values are read from the available on a CD ROM The user can obtain the fieldbus device over the fieldbus using FMS com incremental DD from the device supplier or from the munication services Fieldbus Foundation if the supplier has registered their incremental DD with the Fieldbus Foundation Figure 39 The incremental DDs can also be read directly from the device over the fieldbus if the device supports the upload services and contains a Virtual Field Device VFD for the DD Standard DDs plus optional Incremental DDs _A Number of digits of precision Standard Device Descriptions Engineering Unit from the Fieldbus Foundation Descr
24. ation The User Application object descriptions can start at any index above 255 Index 255 and below define standard data types such as boolean integer float bitstring and data structures that are used to build all other object descriptions Fieldbus Fieldbus Device Device Communication User A S Services MS Figure 23 Object Dictionary Index 0 MINS Index 1 ee Object Description 1 Index 2 Object Description 2 Index n Object Description n Figure 24 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology 3 2 3 1 Virtual Field Device VFD Detailed descriptions for each service are provided A Virtual Field Device VFD is used to remotely in the amp FF 870 Fieldbus Message Specification view local device data described in the object dictio nary A typical device will have at least two VFDs 3 2 3 2 1 Context Management Services Figure 25 The following FMS services are used to establish and release Virtual Communications Relationships Network Management see x FF 801 Network VCR with and determine the status of a VFD Management Specification is part of the Network and System Management Application It provides for the Initiate Establish communications configuration of the communication stack The Virtual Abort Release communications Field Device VFD used for Network Management is Reject Reject improper service also used for System Management This VFD pro Status Rea
25. d Data Transfers The message in the queue is transmitted on the fieldbus when the LAS issues the pass token message to device x The message can be sent to a single destination or to multiple destinations multicast LAS Link Active Scheduler PT x PT Pass Token Fieldbus Live List Device x Figure 20 3 2 1 4 2 Live List Maintenance The list of all devices that are properly responding to the Pass Token PT is called the Live List New devices may be added to the fieldbus at any time The LAS periodically sends Probe Node PN messages to the addresses not in the Live List Ifa device is present at the address and receives the PN it immediately returns a Probe Response PR mes sage If the device answers with a PR the LAS adds the device to the Live List and confirms its addition by sending the device a Node Activation message The LAS is required to probe at least one address after it has completed a cycle of sending PTs to all devices in the Live List The device will remain in the Live List as long as it responds properly to the PTs sent from the LAS The LAS will remove a device from the Live List If the device does not either use the token or immedi ately return it to the LAS after three successive tries Whenever a device is added or removed from the Live List the LAS broadcasts changes to the Live List to all devices This allows each device to main tain a current copy of the Live List
26. d a device status vides access to the Network Management Information Unsolicited Status Send unsolicited status Base NMIB and to the System Management Identify Read vendor type and version Information Base SMIB NMIB data includes Virtual Communication Relationships VCR dynamic vari ables statistics and Link Active Scheduler LAS schedules if the device is a Link Master SMIB data includes device tag and address information and schedules for function block execution 3 2 3 2 2 Object Dictionary Services The following FMS services allow the User Application to access and change the object descriptions OD in a VFD System Management is described further in the User GetOD Read an object aictionary OD Application section InitiateP utO D Start an OD Load PutOD Load an OD into a device oe TerminateP utO D Stop an OD Load 3 2 3 2 Communication Services FMS communication services provide a standardized way for user applications such as function blocks to communicate over the fieldbus Specific FMS com munication services are defined for each object type 3 2 3 2 3 Variable Access Services The following FMS services allow the user application to access and change variables associated with an Object description Read Read a variable Write Write a variable InformationReport Send Data DefineVariableList Define a Variable List Fieldbus Device DeleteVariableList Delete a Variable List All of the FMS services can only
27. defined by approved stan dards from the International Electrotechnical Commission IEC and ISA the international society for measurement and control The Physical Layer receives messages from the communication stack and converts the messages into physical signals on the fieldbus transmission medium and vice versa USER Data FMS PCI USER APPLICATION FIELDBUS MESSAGE SPECIFICATION FIELDBUS ACCESS SUBLAYER USER Encoded Data 0 to 251 4 to 255 Frame Check PCI Sequence DLL DATA LINK LAYER PHYSICAL LAYER 1 1 8 273 Protocol Control Information Fieldbus Protocol Data Unit There may be more than 1 octet of preamble if repeaters are used Figure 10 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology Conversion tasks include adding and removing preambles start delimiters and end delimiters Figure 11 Fieldbus signals are encoded using the well known Manchester Biphase L technique The signal is called synchronous serial because the clock infor mation is embedded in the serial data stream Data is combined with the clock signal to create the fieldbus signal as shown in the figure below The receiver of the fieldbus signal interprets a positive transition in the middle of a bit time as a logical 0 and a negative transition as a logical 1 Figure 12 Special characters are defined for the preamble Start delimiter and
28. e 4 3 1 1 31 25 KOIS FIGIGDUS SINANG 82 di ae hg EA A oe ee ee 5 3 1 2 B17 OKO SFICIGOUS WIINO uta ee hal cor ge tee a Bea BRE REA abe da 6 3 2 COMMUNICATION STACK tica A eo RR Ce eae ees 7 5 2 1 Tne Data Link Layer DLL 20000 a eh tba neasa A Say Mee Rowe ees a Ao e 7 za DEVICE VeSa saunas a eek bao AAA BGs es Ree ew bales wk ae 8 3 2 1 2 Scheduled COMMUNICAUON 2 sexi ius dd de ERAN wees 8 3 2 1 3 Unscheduled Communication sssaaa eaaa eee ene 9 3 2 1 4 Link Active Scheduler Operation 0 0 ce eee eee nes 9 De LA EBSCO SC ta A O le cen sss Se es ss eas BE ecg ne ee hea ois ok 9 IZLA LIVE List MaINtenanTS radial oe A Oo wi Wee Bate Bek ae id Got hee ates A 9 3 2 1 4 3 Data Link Time Synchronization 1 0 ee eens 10 3 2 14 4 TOKEN PASSING irradia ada be wee ed eae SS 10 Aldo LAS REGUNGANCY stud ira oo we eae AAA 10 3 2 2 Fieldbus Access Sublayer FAS ar A A eae SE 10 3 22 4 CUENV SEE VOR TVE cara e sd ta bio 10 3 2 2 2 REDON DIStIDUION VER TUDO currar A aaa 10 5 2125 PUDIISNET SUDSCIIDEr VCR TDS AAA AAA 11 ile SUMMA OF WERTVDOS ss cia aa ads dia a we Ree eed dd dd 11 3 2 3 Fieldbus Message Specification EMS ooooooorrrnrna eens 11 3 2341 Virtual Field Device VED estern n arras ar e aa 12 3232 GOMMUNICALON SEIVICES 2 vedado ais a Weems Aa 12 O 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Table of Contents 4 0 5 0 6 0 7 0 8 0 9 0 3 2 3 2 1 Context
29. e input to help ensure the specifications meet the needs of the marketplace 2 1 5 Quality Director The Quality Director provides overall management of the foundation s quality assurance systems 2 1 6 Executive Committee The Executive Committee advises the President con cerning the strategic and overall operational issues of the foundation 2 1 7 Technical Teams The Technical Teams are responsible for the techni cal work of the foundation The technical work is grouped into programs such as Specifications Software and Interoperability Testing A Program Manager Is responsible for each technical program 2 1 8 Marketing Teams The Marketing Teams are responsible for promoting FOUNDATION fieldbus and for planning and directing the foundation s products and services 2 1 9 Member Support Member Support is responsible for coordination and delivery of the Foundation s products and services Products and services include technical consulting and training newsletter printing and distribution memberships coordination of trade shows and field tests product catalogs Device Description software and device registrations 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved 3 0 FOUNDATION FIELDBUS TECHNOLOGY ta FF 800 System Architecture Specification Note References to specific documents are noted as follows th Document number and name FOUNDATION fieldbus technology consists of 1 the
30. ed forward into the boiler feedwater system The configuration device generates all of the information needed to set up the fieldbus Configuration Device Systems Engineer Device Descriptions LEER ES OS Network Setup VCR Setup Device Address List Initial Values Network Setup VCR Setup TAG Setup N Link Object Setup Initial Values Function Block Schedules LAS Schedule Active Standby LAS Fieldbus Figure 45 Link Master Device Basic Devices 5 1 Test Instrumentation Fieldbus transmitter instrumentation installed on the system included e level on each tank and across both tanks e pressure on the flash tank e flow on the boiler feedwater system e total pump flow e recycle flow The control valves were equipped with digital positioners which were used to control the boiler feedwater treatment and recycle flow The instruments were connected to one of two fieldbuses connected to a distributed control sys tem DCS located in the utilities control room The installation used a combination of existing twisted pair wiring and new wiring While not required by the process intrinsic safety barriers were demonstrated on the system Performance of the fieldbus was monitored by bus analyzers Condensate from Header Field Test System PT 105 0 cv 202 FT 201 CV 103 TT 104 O To Water e Treatment FT 102 Figure 46 O 1996 Rev 1998 Fieldbus Foundation Austin Texas
31. iba yster Figure 48 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved References FD 100 DDL Tokenizer User s Manual FD 110 DDS User s Guide FD 200 Conformance Tester User s Guide FD 210 Interoperability Tester User s Guide 7 REFERENCES 1 Fieldbus Standard for Use in Industrial Control Systems Part 2 Physical Layer Specifications and Service Definition ISA 50 02 1992 2 International Standard for Use in Industrial Control 8 ACRONYM TABLE Systems Part 2 Physical Layer Specifications and Service Definition IEC 61158 2 1993 Abstract Syntax Notation 1 International Telegraph and Telephone Consultative Committee Compel Data Direct Current Distributed Control System Device Description Device Description Language Device Description Services Data Link Layer End User Council Fieldbus Access Sublayer Function Block Fieldbus Foundation Fieldbus Message Specification High Speed Ethernet Gigabits per second ASN 1 CCITT 3 Digital data communications for measurement and control Fieldbus for use in industrial control systems Part 3 Data Link Service Definition and Part 4 Data Link Protocol Specification 61158 DIS IEC SC65C WG6 ISA SP50 1994 1998 CD DCS DDL DDS DLL EUC FAS 4 FOUNDATION Fieldbus Specifications Revision 1 3 Fieldbus Foundation 1994 1998 5 Benefits Observed During Field Trials Of An Interoperable Fieldbus Kurt A Zech Fieldbus F
32. ion Blocks for advanced control are defined in the Un FF 892 Function Blocks Part 3 specification Function blocks can be built into fieldbus devices as needed to achieve the desired device functionality For example a simple temperature transmitter may contain an Al function block A control valve might contain a PID function block as well as the expected AO block Thus a complete control loop can be built using only a simple transmitter and a control valve Figure 30 3 3 3 Transducer Blocks Transducer Blocks decouple Function Blocks from the local input output functions required to read sensors and command output hardware They con tain information such as calibration date and sensor type There is usually one transducer block for each input or output function block The following additional objects are defined in the User Application Link Objects define the links between Function Block inputs and outputs internal to the device and across the fieldbus network Trend Objects allow local trending of function block parameters for access by hosts or other devices Alert Objects allow reporting of alarms and events on the fieldbus View Objects are predefined groupings of block parameter sets that can be used by the human machine interface The function block specification defines four views for each type of block Example of a complete control loop using Function Blocks located in fieldbus devices Device 1
33. iptions are read from the DD Incremental Device Descriptions from Suppliers Device Description Host Services Library Application EE SEESEESE a Data are read from the device over the fieldbus Figure 39 Figure 40 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology New devices are added to the fieldbus by simply connecting the device to the fieldbus wire and pro viding the control system or host with the standard and incremental if any DD for the new device Figure 41 DDS technology allows operation of devices from different suppliers on the same fieldbus with only one version of the host human interface program 3 5 3 Device Description Hierarc hy The Fieldbus Foundation has defined a hierarchy of Device Descriptions DD to make it easier to build devices and perform system configuration The hierarchy is shown in Figure 42 The first level in the hierarchy is the Universal Parameters Universal Parameters consist of com mon attributes such as Tag Revision Mode etc All blocks must include the Universal Parameters The next level in the hierarchy is the Function Block Parameters At this level parameters are defined for the standard Function Blocks Parameters for the standard Resource Block are also defined at this level DD Services Device from iE Device Supplier A Y Descriptions Supplier Z Fieldbus Figure 41 The third level is called Tra
34. irtual Field Device VFD in each device This VFD provides access to the System Management Information Base SMIB and also to the Network Management Information Base NMIB Function Block Application m OD Header Application Resource Block Object Descriptions Figure 34 Transducer Block ee ee Link Objects i A Trend Objects i Function Block User j Virtual Field Device r Physical Layer Fieldbus 3 4 1 Function Block Scheduling A schedule building tool is used to generate func tion block and Link Active Scheduler LAS sched ules Assume that the schedule building tool has built the following schedules for the loop previously described in Figure 30 The schedules contain the start time offset from the beginning of the absolute link schedule start time The absolute link schedule start time is known by all devices on the fieldbus Figure 35 A macrocycle is a single iteration of a schedule within a device The following figure shows the rela tionships between the absolute link schedule start time LAS macrocycle device macrocycles and the start time offsets Offset from Absolute Link Schedule Start Time Scheduled Al Function Block Extension 0 Scheduled Communications of Al 20 Scheduled PID Function Block Execution 30 Scheduled AO Function Block Execution 50 Figure 35 O 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved In Figure 3
35. it s devices can be powered directly from the fieldbus and operate on wiring previously used for 4 20 mA devices The 31 25 kbit s fieldbus allows stubs or spurs Figure 15 The 31 25 kbit s fieldbus also supports intrinsically safe 1 S fieldbuses with bus powered devices To The length of the fieldbus is determined by the accomplish this an I S barrier is placed between communication rate cable type wire size bus the power supply in the safe area and the I S power option and I S option device in the hazardous area Signaling waveforms for the 31 25 kbit s Fieldbus Control Room Devices Spur Length Fieldbus Device 25 32 1 metre 19 24 30 metres Junction 15 18 60 metres B 13 14 90 metres 15 to 20 mA p p Fieldbus Signal 120 metres Device Current A 0 j Receiving Transmitting eee pri 75 to 1 0 V p p Power 9 to 32 Volts Maximum Length 1900 metres with Type A Cable Cable Length Trunk Length All Spur Lengths M y A terminator is installed at each end of the main trunk cable Y Single device per spur The spur length must be reduced by 30 Y Terminator metres for each additional device on a spur Fieldbus Network C is sized to pass 31 25 kbit s kkx E 3 The number of devices possible on the fieldbus will vary depending on factors such as the power consumption of each device the type of cable used use of repeaters etc Consult the Physical La
36. networks due to possible distribution of some control and Figure 2 input output functions to field devices e connection to a High Speed Ethernet backbone The fieldbus retains the desirable features of the 4 20 for larger systems milliampere mA analog system such as a standardized physical interface to the wire 1 1 Fieldbus Benefits g devi ndeni Significant benefits are achieved in the control RAE a ae system life cycle through the application of e intrinsic safety options fieldbus technology Figure 3 Fieldbus LAN Office Automation and Departmental Plant Wide Computers Network Automation Control and Automation Systems and LANs Display Systems and ss i Display Systems Fieldbus Fade lots Network nstrumentation Entra cion and Control Devices Figure 1 Figure 2 Planning and Operation Maintenance Evolution Installation Reduced number of wires and marshaling panels Reduced number of intrinsic safety barriers Reduced number of input output converters Reduced number of power supplies and cabinets Reduced size of equipment rooms Remote configuration of devices More information available for operations Increased accuracy of measurements Easier evolution due to standardized function blocks Increased sophistication and flexibility of instrumentation Increased uptime due to less equipment better self diagnostics and remote diagnostics Figure 3 O 1996 Rev 1998 Fieldbus Foundation Austin Texa
37. nsducer Block Parameters At this level parameters are defined for the standard Transducer Blocks In some cases the transducer block specification may add parame ters to the standard Resource Block The Fieldbus Foundation has written the Device Descriptions for the first three layers of the hierarchy These are the standard Fieldbus Foundation DDs The fourth level of the hierarchy is called Manufacturer Specific Parameters At this level each manufacturer Is free to add additional parameters to the Function Block Parameters and Transducer Block Parameters These new parameters will be included in the incremental DD discussed earlier Universal Parameters Defined Function by Block Fieldbus Foundation Parameters Specification Transducer Block Parameters Defined by Manufacturer Specific Manufacturer Parameters Resource Transducer Function Block Blocks Blocks Figure 42 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved 3 5 4 Interoperability a FD 210 Interoperability Tester User s Guide Each manufacturer will provide the Fieldbus Foundation with an interoperability test report for each device The test report identifies the Universal Function Block Transducer Block and Manufacturer Specific Parameters in the device An identifier called the Manufacturer s Identification is used to correlate the device type and revision with its Device Description and DD revision
38. of the emerging IEC ISA DLL standard USER USER APPLICATION APPLICATION FIELDBUS MESSAGE SPECIFICATION FIELDBUS ACCESS SUBLAYER COMMUNICATION STACK DATA LINK LAYER PHYSICAL LAYER PHYSICAL LAYER Figure 17 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology 3 2 1 1 Device Types 3 2 1 2 Scheduled Communication Two types of devices are defined in the DLL specifi The Link Active Scheduler LAS has a list of trans cation mit times for all data buffers in all devices that need to be cyclically transmitted e Basic Device e Link Master When it is time for a device to send a buffer the LAS issues a Compel Data CD message to the Link Master devices are capable of becoming the device Link Active Scheduler LAS Basic devices do not have the capability to become the LAS Figure 18 Upon receipt of the CD the device broadcasts or publishes the data in the buffer to all devices on the fieldbus Any device configured to receive the data is called a subscriber Figure 19 Scheduled data transfers are typically used for the regular cyclic transfer of control loop data between devices on the fieldbus Scheduled Data Transfers The message in the data buffer is broadcast to all devices on the fieldbus when the LAS issues the compel data to the publisher The subscribers listen to the message broadcast Schedule LAS Link Active Scheduler ari Da gt
39. organization based on the following principles e Fieldbus technology is an enabling technology not a differentiating technology e Fieldbus technology is open and available to all parties e Fieldbus technology is based on the work of the International Electrotechnical Commission IEC and ISA the international society for measurement and control e Fieldbus Foundation members support and work in the standards committees 2 1 Organization The Fieldbus Foundation is organized as in Figure 8 MEMBERS OF DIRECTORS PRESIDENT QUALITY DIRECTOR TECHNICAL MARKETING MEMBER TEAMS TEAMS SUPPORT Figure 8 END USER COUNCILS EXECUTIVE COMMITTEE 2 1 1 Members The Fieldbus Foundation has over 130 member companies These companies supply over 90 of the world s instrumentation and control products 2 1 2 Board of Directors The foundation is managed under the direction of the Board of Directors BOD The BOD Is elected by the voting members 2 1 3 President The President reports to the Board of Directors manages the day to day activities of the Fieldbus Foundation and provides direction for the Executive Technical Marketing and Member Support functions 2 1 4 End User Councils The End User Councils EUC are comprised of users of fieldbus equipment There are EUCs in North America Europe Latin America and Asia Pacific The purpose of the EUC is to review the activities of the foundation and provid
40. oundation Paper 94 504 ISA 1994 FMS HSE 6 Abstract Syntax Notation One ASN 1 The Tutorial Gbit s and Reference Douglas Steedman Technology EC International Electrotechnical Commission Appraisals Ltd 1993 ISBN 1 871802 06 7 Intrinsically Safe IS The International Society of Measurement and Control International Organization of Standards kilobits per second kilohertz Local Area Network Link Active Scheduler Milllampere Megabits per second Network Management Information Database Object Dictionar Open Systems Interconnect Personal Computer Protocol Data Unit z Im Nm 8 DOCUMENT LIST T kbit s The following documents are available from the Fieldbus Foundation LAS AG 140 AG 163 31 25 kbit s Wiring and Installation Guide 31 25 kbit s Intrinsically Safe Systems Application Guide Fieldbus Installation and Planning Guide System Architecture Specification Network Management Specification 31 25 kbit s Physical Layer P rofile Specification M bit s NMIB AG 165 FF 800 FF 801 FF 816 OSI PDU FF 818 FF 821 FF 822 FF 880 FF 870 FF 875 FF 890 FF 891 FF 891 FF 900 FF 940 31 25 kbit s Fiber Optic Physical Layer Profile Data Link Layer Services Subset Specification Data Link Layer Protocol Specification System Management Specification Fieldbus Message Specification Fieldbus Access Sublayer Specification Function Blocks Part 1 Function Blocks Part 2 Function Blocks Part 3
41. oundation be responsible for any loss or damage arising out of or resulting from any defect error or omission in this document or from anyone s use of or reliance on this document 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Table of Contents 1 0 WHAT IS FOUNDATION FIELDBUS o eee ens 1 1 1 Fieldbus Benefits 000 ai id AA A eee e EA A A IA Oe 1 LIL Morte Data AValablO 353 Es a ai de ro oa ee dae ae 2 1 1 2 Expanded View Of the ProceSS cc eee eee eee n es 2 LL33 REQUCHO NIN System HardWale ceases See ie asec AA te ee Be wi af AE eee Mec ones Gates Hee 2 ELA Wing SAVNO S Se eons cb cece ho he sas ia a de Seay daba do 2 2 0 WHAT IS THE FIELDBUS FOUNDATION caa ees 3 2 1 Organization ardid dws Cee e VSR ewe See USES aR ae es 3 Pll Memes o aap te cic o td loa o ao atc BE 3 22 BOa rd OT DE CO S aera a e eA eS Ba ee a erae ae aoe Ps a we 3 A A A ae eed a a eee 3 DAA EWG US Er C OUNCHS ddr ead aon eae area oan Rae a a eee Sao ee A 3 A A O get ee an ek 3 PMO We XOCULIVE COMMING seca acs do ieee oe ae Ste cad wt ak ace Ge ae at mate eT et ica e evi teat a dr 3 Zabel TECHNICA CAMS sos bia on AAA e One ew hee ea AA e e ne 3 ZAC Marketing TEAMS srar twa oe ant aS eee Chae ona eee oes as beds eae 3 LL Member SUDOR aa bee e ARI AR NA AAA 3 3 0 FOUNDATION FIELDBUS TECHNOLOGY o cccccocococcoccnc eee 4 3 4 Physical Layer 31 25 KOWS aos ra eid AA A E AS AAA ee e
42. s All rights reserved Introduction 1 1 1 More Data Available The fieldbus allows multiple variables from each device to be brought into the control system for archival trend analysis process optimization stud les and report generation The high resolution and distortion free characteristics of digital communica tions enables improved control capability which can increase product yields Figure 4 1 1 2 Expanded View of the Process The self test and communication capabilities of microprocessor based fieldbus devices helps reduce downtime and improve plant safety Upon detection of abnormal conditions or the need for preventive maintenance plant operations and maintenance personnel can be notified This allows corrective action to be initiated quickly and safely Figure 5 1 1 3 Reduction in System Hardware FOUNDATION fieldbus uses standard Control System E Control System Network Network Controller Fieldbus Traditional 4 20 mA One Variable One Direction Fieldbus Multiple Variables Both Directions Figure 4 _ ff Control System E Control System r Network a Network Controller Traditional Fieldbus Some control and I O can move to field Figure 6 instruments Function Blocks to implement the control strategy Function Blocks are standardized automation functions Many control system functions such as analog input Al analog output AO and Proportional Integral Derivative
43. ships VCR The VCR is like the speed dial feature on your mem ory telephone There are many digits to dial for an international call such as international access code country code city code exchange code and finally the specific telephone number This information only needs to be entered once and then a speed dial number is assigned After setup only the speed dial number needs to be entered for the dialing to occur Likewise after configuration only the VCR number is needed to communicate with another fieldbus device J ust as there are different types of telephone calls such as person to person collect or conference calls there are different types of VCRs Technology 3 2 2 1 Client Server VCR Type The Client Server VCR Type is used for queued unscheduled user initiated one to one commu nication between devices on the fieldbus Queued means that messages are sent and received in the order submitted for transmission according to their priority without overwriting previous messages When a device receives a Pass Token PT from the LAS it may send a request message to another device on the fieldbus The requester is called the Client and the device that received the request is called the Server The Server sends the response when it receives a PT from the LAS The Client Server VCR Type is used for operator initiated requests such as setpoint changes tuning parameter access and change
44. tic menus Figure 37 Device Description DD technology is used in addition to standard function block parameter and behavior definitions The DD provides an extended description of each object in the Virtual Field Device VFD as shown in Figure 37 The DD provides information needed for a control system or host to understand the meaning of the data in the VFD including the human interface for functions such as calibration and diagnostics Thus the DD can be thought of as a driver for the device The DDs are similar to the drivers that your personal computer PC uses to operate different printers and other devices that are connected to the PC Any control system or host can operate with the device if it has the device s DD 3 5 1 Device Description Tokenizer ta FD 900 Device Description Language Specification ta FD 100 DDL Tokenizer User s Manual The DD is written in a standardized programming language known as Device Description Language DDL A PC based tool called the Tokenizer con verts DD source input files into DD output files by replacing key words and standard strings in the source file with fixed tokens as shown in Figure 38 DDL Source File VARIABLE ProcessVariable LABEL MEASURED _ VALUE TYPE FLOAT DISPLAY_FORMAT 3 1f MAX_VALUE 110 0 MIN VALUE 0 0 DD Output File 009 101 002 MEASURED_VALUE 001 010 061 3 1f 021 066 220 000 000 020 000 000 000 000
45. tion PI allows the execution of a program in one device to be controlled remotely A device could download a program into a Domain see previous section of another device using the download service and then remotely operate the program by issuing PI service requests The state diagram for the Pl is shown as an exam ple of FMS protocol behavior later in this document CreateP rograminvocation Create a program object DeleteP rogramInvocation Delete a program object Start Start a program Stop Stop a program Resume Resume program execution Reset Reset the program Kill Remove the program 3 2 3 3 Message Formatting ASN 1 Tutorial and Reference Steedman The exact formatting of FMS messages is defined by a formal syntax description language called Abstract Syntax Notation 1 ASN 1 ASN 1 was developed by the International Telegraph and Telephone Consultative Committee CCITT in the early 1980s as a part of the CCITT mail stan dardization activities See Figure 26 for a partial example of ASN 1 defini tion for the FMS Read service Read_Request SEQUENCE Access specification CHOICE index variable name variable list name 0 IMPLICIT Index 1 IMPLICIT Name 2 IMPLICIT Name sub index 3 IMPLICIT Subindex OPTIONAL User Application ASN 1 Definition of a Read_Request Figure 26 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology
46. tion items such as device names loop tags and loop execution rate have been entered the configuration device generates information for each fieldbus device TRANSMITTER FIELDBUS DEVICE VALVE FIELDBUS DEVICE Figure 44 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Field Test A stand alone loop can be configured if there is a field device that is a Link Master This will allow continued operation of the loop without the configu ration device or a central console Figure 45 The system becomes operational after the field bus devices have received their configurations 5 FIELD TEST SYSTEM Benefits of fieldbus technology were directly observed during field tests on real processes This section gives the results of one of the tests Fieldbus devices were installed on a condensate recovery system in a utilities plant The recovery system receives the steam conden Sate returning to the utilities plant from the rest of the site and returns this condensate into the water treatment system Figure 46 The process consists of two tanks a flash tank which is approximately 85 gallons and a condensate tank of approximately 20 gallons The flash tank is mounted directly above the other tank The returning condensate flows into the flash tank where lowering of pressure may cause the conden Sate to flash to steam The liquid condensate flows down into the condensate tank from which it is pump
47. use the Client Server VCR Type except as noted Network and System Function Management Block Can use Publisher Subscriber or Report Sid Sa Distribution VCR Types Network and System Management 3 2 3 2 4 Event Services The following FMS services allow the user applica tion to report events and manage event processing EventNotification Report an event AcknowledgeEventNotification Acknowledge an event AlterEventC onditionM onitoring Disable Enable event FIELDBUS Can use Report Distribution VCR Type 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Figure 25 Technology 3 2 3 2 5 Upload Download Services It is often necessary to remotely upload or down load data and programs over the fieldbus especially for more complex devices such as programmable logic controllers To allow uploads and downloads using the FMS services a Domain is used A Domain represents a memory space in a device The following FMS services allow the User Application to upload and download a Domain in a remote device RequestDomainUpload Request Upload InitiateU ploadSequence Open Upload UploadSegment Read data from device TerminateUploadSequence Stop Upload RequestDomainDownload InitiateDownloadS equence DownloadSegment Request Download Open Download Send data to device TerminateDownloadSequence Stop Download 3 2 3 2 6 Program Invocation Services The Program Invoca
48. yer Standard for details Figure 14 Figure 15 Note As an option one of the terminators may be center tapped and grounded to prevent voltage buildup on the fieldbus 1996 Rev 1998 Fieldbus Foundation Austin Texas All rights reserved Technology Figure 16 gives a summary of examples of options available in the Physical Layer standard 3 2 Communication Stack The following sections will describe the operation of the layers in the Communication Stack Figure 17 3 2 1 The Data Link Layer DLL ta FF 821 Data Link Layer Services Subset Specification tn FF 822 Data Link Layer Protocol Subset Specification Characteristics Data Rate 31 25 kbit s 31 25 kbit s 31 25 kbit s Type Voltage Voltage Voltage Topology Bus tree Bus tree Bus tree Bus Power none DC DC Classification Intrinsically Safe Number of Devices 2 32 2 6 Cable Length 1900 m 1900 m Spur Length 120 m 120 m Figure 16 The number of devices possible on a fieldbus link depends on factors such as the power consumption of each device the type of cable used use of repeaters etc Consult the Physical Layer Standard for details The number of network addresses available for each link is 240 Layer 2 the Data Link Layer DLL controls trans mission of messages onto the fieldbus The DLL manages access to the fieldbus through a determin istic centralized bus scheduler called the Link Active Scheduler LAS The DLL is a subset
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