maxDNA An Overview METSO AUTOMATION MAX CONTROLS
Key Learning Overview of maxDNA control system The maxDNA Plant Automation System (PAS) is the latest version of Distributed control system developed by Metso Automation MAX Controls, US. maxDNA works with the popular operating systems Microsoft Windows 2000/XP and Windows
communications and Distributed Processing Units (DPUs), to give an open architecture and reliable control system. The maxDNA DDCMIS follows a multi-level hierarchy. The lowest or first level interacts with the actual plant by acquiring the parameters/status, and issuing the actuating signals/commands. This is done by the I/O modules. The second level performs closed loop control and open loop control, which is accomplished through execution of atomic blocks by DPU in maxDNA. The operator console or the Operator’s Workstation (OWS), and the supervisory console or the Engineer’s Workstation (EWS), are at the third level. At the highest level, called Enterprise Management Network, engineers and managers have access to the entire system database.
The system consists of the following components: •
maxNET, a redundant Fast Ethernet network for communication
maxDPU4E, Distributed Processing Units providing control and data acquisition
maxPAC I/O Modules interfacing with the plant I/O
maxSTATIONs providing the human interface with the system
maxSTORIAN for historical storage and retrieval
maxLINKS for multi-protocol connectivity with external devices
maxOPC for OLE (Object Linking & Embedding) data interchange between clients.
maxDNA software runs on popular Microsoft platforms. maxSTATIONs have Windows XP operating system while DPUs have the compact version of Windows CE installed. The attractive features of maxDNA software for the benefit of the engineer or operator are: • • • • • •
High level object-oriented programming in Graphical User Interface (GUI) Wide selection of standard library functions Provision for user-defined multi-function expandability User flexibility in assigning inputs/outputs Unique address for I/O signals Service kit (Software Development Kit or SDK)
The maxDNA software package can be categorized as given below: Configuration Software • maxTOOLS4E -- offline configuration tool for EWS • maxVUE Graphical Configurator -- online configuration tool for OWS General Utilities • Serverless Software Backplane (SBP) -- for subscription-based services on maxNET • Remote SBP -- Provides the ability to monitor the maxDNA system from a remote location by connecting into a selected workstation via a modem or LAN connection • MaxCALCS -- Package to build calculations • MaxAPPS -- Application development tool kit DPU4E System Software • PointBrowser -- used to view and edit a DPU4E point database online • HealthLog -- monitors health of DPUs in your system • BadPointReference -- flags bad references in point database • DownloadFreezeCheck -- unfreezes outputs after a download • MaxMergeDPUAlm -- produces a merged alarm list derived from multiple DPUs
maxPROXY -- runs when a workstation is configured as a proxy server TimeSync -- used to set up system time masters per domain
2.2 maxNET Communication network maxNET incorporates 100Mbps Fast Ethernet with Full Duplex Switches, Software Backplane middleware based on subscription services and User Datagram Protocol in the network layer of the OSI model. maxNET connects all of the DPUs to each other via switches, and links the maxSTATIONs used by operators, engineers and managers into a high-speed, reliable and well-integrated system. The link between the Fast Ethernet switches is of 100 Mbps transfer rate, while the links that connect maxSTATIONs and DPUs with the switches are of 10 Mbps. maxNET supports real-time redundancy of networks and does not wait for extensive TCP/IP timeouts before making use of alternate network channels.
maxNET detailed architecture
Software Backplane interface
The Serverless Software Backplane© is a plug-and-play middleware environment that allows maxDNA applications to easily communicate with each other. It is the inter-application communication protocol cum connectivity module of maxNET. It provides a common information interchange format that allows any application with a need, to acquire information from any other application. Information provided through the SBP is available to maxSTATIONs (maxVUE and maxTOOLS), DPUs, maxSTORIAN, maxLINKS etc. The SBP uses subscription services where data is only transmitted when changes are detected. SBP Software Suite •
maxRRS (Registration and Routing): the core of the SBP, this program is responsible for connecting clients with providers of information. Providers ‘register’ information on the SBP. Clients ‘read’, ‘write’ and ‘subscribe’ to that information through the SBP. MaxLSS (Local Status Server): provides a number of housekeeping functions. These include storage for other processes (such as the last display and selected point for MAXVUE) as well as a set of simulation functions. MCS Real Time Gateway (RTG): provides an interface between the Data Bus Module (DBM) and the SBP. The RTG provides immediate data, trend data, alarm data etc. MCS Transport Daemon (MAXT): checks healthiness of other workstations by pinging. maxAlarmMerge(maxAM): Support for alarm summary and lists.
2.3 maxDPU4E Distributed Processing Unit Features
A DPU consists of a motherboard supporting the Control Processor (CPU) and Input/Output Processor (IOP). The CPU is a Pentium processor with 8 MB of flash EPROM and 32/64 MB of RAM. The DPU chassis panel contains 2 serial ports, 2 maxNET interface ports, 1 backup link port, 3 rotary address switches, 1
mode switch and 1 key switch. The DPU front panel contains 3 network status LEDs, 2 serial port LEDs, 4 IOM status LEDs, 3 hardware status LEDs, DPU state LEDs, reset button and takeover button. Redundancy & Download
A primary and secondary DPU are selected through configuration. Either DPU of a pair can be designated the primary. When a fatal diagnostic error is detected control is automatically transferred to the secondary so that it now becomes the primary. A fully enforced object oriented design allows encapsulation of control elements to prevent inadvertent upsets during downloads and test of new control strategies. Processing Capabilities
A multi-speed processing system is built into the maxDPU4E, which allows objects to be executed in three different time classes - 20 ms, 100 ms and 500 ms. Up to 6,000 atomic blocks can be executed in the DPU. Atomic blocks can be combined into standard and custom function blocks that provide complete control and alarming for an entire plant equipment group. A distributed point management system keeps track of the object size and the total execution time for each time class. Sequence of Events
Each DPU can monitor up to 500 discrete inputs as a built-in Sequence-of-Events (SOE) recorder. These inputs are scanned 1,000 times a second and state changes are time stamped with 1 ms resolution and stored in the DPU's 10,000 event buffer. Each input has a separately configurable digital filter for contact debounce. Comprehensive Alarming
Each alarm block identifies up to 16 alarm conditions as a digital status. This permits sophisticated interlocking control strategies with all other DPU functions. Each data block provides a wide range of data acquisition alarm features including multi-level, rate-of-change, and repetitive delta alarms, adjustable hysterisis, time delays, re-alarm, and auto-acknowledge features. All alarms are
time tagged by the DPU and placed in the 10,000-event buffer for de-queueing by the maxSTATIONs. Quality Coding
All data within the DPU is marked with a quality code in addition to the output value. Four quality states are identified Good (0), Doubtful (1), Substitute (2) and Bad (3). The quality code is propagated throughout the system to be included by trend and archive data. Timing
maxDPU4E time stamps process alarms and events based on its internal clock. The DPU clock time is periodically updated through maxNET based on the stable time source within one of the maxSTATIONs. For high stability an IRIG-B clock receiver can be mounted directly on the DPU and connected via the third Ethernet port. Programming
Programming the DPU is done through the IEC 1131-3 toolset in maxTOOLS4E. DPU Redundant Operation •
Automatic Failover: Process control is automatically transferred from the
primary DPU to the secondary DPU or vice versa in less than 3 ms when the first DPU experiences a severe diagnostic alarm or when the communication between the two is lost. However, if the secondary DPU is itself experiencing a severe diagnostic alarm, it will refuse control, unless the primary DPU loses power or is reset. •
Manual Takeover: To manually command either DPU to assume control, the
takeover button on the front panel of the unit has to be pressed. Manual takeover will occur only if the inactive DPU is healthy enough to assume control. If a severe diagnostic alarm or a fatal alarm condition exists in the inactive DPU then the Take button will be ignored.
The following backup states are used to decide which DPU will remain or assume control: 1. Fully Healthy or Healthy Enough (DPU ready): •
DPU has some I/O errors below threshold
Net A and/or Net B functional (outage of one for >5 min persistence)
DPU active but can’t hear backup
2. Some Errors (DPU would rather not run): •
I/O errors above threshold while some IO good
Net A and/or Net B functional (outage of one for more than 5 minutes)
3. Serious Errors (DPU will only run if necessary): •
IOM Diagnostic errors
Net A and Net B both non-functional
Database out of date
All I/O Bad
4. Fatal Errors (DPU cannot run regardless): .
DPU total failure
2.4 I/O system: maxPAC
The maxPAC Input/Output System links the maxDNA DCS to real world process control I/O. The DPUs and the I/O modules mount in an I/O chassis assembly with a backplane to provide the I/O bus connection. The maxPAC I/O System uses the Model APS Power Supply Assembly, which provides 11V dc power for DPUs and I/O. Because each module is individually isolated, the chassis can be split to provide both system power and loop power. Addresses must be set for each I/O module using the rotary switches which permit 156 logical addresses. maxPAC is a family of I/O modules and racks that offers the user space saving, high density I/O that is designed and built to withstand the harsh electrical environment found in power plants and other high current switching environments. The I/O modules are constructed of glass epoxy multi-layer printed circuit cards with gold plated contact surfaces that mate with gold plated connectors in the backplane of the rack that supports the modules.
I/O Configuration Options
There are three ways to provide for redundancy of the I/O modules and the I/O bus: i)
Shared • • •
1 set of I/O modules 1 I/O bus 1 DPUs connected with backup cable and with I/O bus looped to both
Mixed • • •
3 sets of I/O modules (primary, secondary, and common) 3 I/O buses 1 DPUs connected with backup cable and with common and separate bus
Independent • • •
1 sets of I/O modules (primary & secondary) 1 I/O buses (primary & secondary) 1 DPUs connected with backup cable, each with its own I/O bus and I/O modules
Independent Configuration I/O Bus •
10 microsecond transfers
8-bit parallel asynchronous I/O bus
Parity checks are performed on all I/O
LSI bus interface circuitry for better reliability
Check-before-execute control strategy for output signals
Module address verification and multiple module detection checks
• Bus fault detection by automatic confirmation of input data on every module
I/O signals •
Normal or common mode rejection (IEEE-171, ANSI c37.90)
Common mode transients bypassed to chassis metal work
All points optically or transformer-isolated from the I/O bus
Channel-to-channel isolation allows series or parallel connections
Logic state indication on the front panel for digital modules
List of Analog modules
No. of channels
I or V input
No. of channels
Form C output
Form A/B output
List of Digital modules
2.5 Workstation maxStation MMI functions The MMI part of the maxDNA DCS is expected to perform the following functions. • Manual control: Actuators, motors of fans/pumps, valves • Command & setting: Transfer control modes, adjusting set point • Display: Status, position, measured value, control modes, trends
• • • •
Annunciation: Plant alarms, instrument faults Record: Plant events, operator actions Print: Logs, reports, Sequence of Events Configuration: Control loops, mimics, tuning.
History maxSTORIAN Process History is a highly efficient and flexible data collector/compression application that acquires user-specified information on a periodic basis, checks for changes between sample periods, and stores the sampled values on the 40GB RAID disk (Redundant Array of Inexpensive Disks). Users can archive process history data to CD-ROMs (typically message prompts for download at 80% of the disk capacity). The tool time-stamps data at the source whenever the event or process variable changes. maxLINKS
maxLINKS is an application software run on a maxSTATION providing 16-channel multi-protocol connectivity between the maxDNA system and external devices. The user can export and import critical process data to/from external subsystems of electrical protection, fire protection, manufacturer’s PLCs, RTUs, turbine control systems, precipitators, ash handling, sootblowers, water analysis, condensate polishing, vibration measuring etc. The protocols supported include Modbus RTU, AB, Conitel RTU, GE Mark V turbine control etc. A maxLINKS server has the capability to interface with 8 systems, and can store upto 10,000 points. The functions of maxLINKS are: • • •
Configuration of services, members and underlying layers (helper and transport DLLs) Response to the SBP for Read/Write/Subscribe on the configured points Core libraries (Immediate data acquisition), Helper and transport libraries
maxOPC server and the configuration tools provide a secure, easily managed data exchange interface to plant and enterprise management application software that must acquire real-time information from the maxDNA plant automation system. maxOPC server is based on OPC (OLE for Process Control), a leading industry standard which defines a method of exchanging real-time automation data among PC based clients using Microsoft operating systems. OLE stands for Object Linking & Embedding, which means the ability to use different file or objects in a single application through appropriate linking with their parent applications. maxOPC can either read values directly from a DPU or use maxSTORIAN as a cache data source providing higher capacity and faster performance with reduced system loading. Additionally, when maxSTORIAN is used as the data source, it is typically installed on the same workstation as the maxOPC server to reduce subscription loading to DPUs.
Data access is configured through a maxOPC configuration server grid window and a number of OPC configuration dialog boxes that prompt the user for tag names, attributes, read/write privileges, and their on-data-change parameters in terms of SBP delta, min/max times. This provides control over data access security and performance loading. Key Features •
Provides secure OPC client read/write data access to SBP data
Supports demand writes and on-data-change and polling reads
Access up to 300 values when direct access to maxDPU4E is used
Access up to 2000 values maxSTORIAN is used as an exclusive cache source
2.6 Building blocks
Atomic blocks form the basis of all control or logic implementation. They are the building blocks of the Closed Loop as well as Open Loop Control Systems (CLCS and OLCS). They are software objects that encapsulate specific engineering functionality, such as a PID, an Auto/Manual toggle switch or an AND gate. Atomic Blocks are normally grouped into larger objects to encapsulate increased functionality. Groups of atomic blocks constitute a custom function block object. Custom function blocks can be applied in hierarchical identification levels (HID levels) to form increasing levels of control system functionality. These HID levels can then be assigned to a particular DPU. Atomic Blocks, buffers, and custom function blocks are part of a DPMS (Distributed Point Management System), a Microsoft Access-style database and client/server that composes a Distributed Processing Unit (DPU). The DPMS manages its point database, provides master scheduling, and executes the objects composing its database, among its various functions.
The data stored in an atomic block is organized as a set of attributes. All attributes have subattributes like category, description, reference, attrwriteable, attrreadable attrminval etc. The attributes may be divided into the following categories: General
Foundation attributes required by all atomic blocks.
Values usually obtained by referencing another attribute.
Similar to inputs except that local value is used instead of reference. They are predominantly used to configure the atomic block.
Values that are the result of the function or operation with which they are associated. They are used to generate data for other atomic blocks.
Similar to outputs, they are predominantly used to monitor the atomic blocks’ execution.
The behavior of atomic blocks may be based on the Quality of its inputs. Methods direct an atomic block to perform a special function. Eg. to change mode or target value, etc. Attributes that are used to receive commands from the HMI that will initiate some action within the atomic blocks’ algorithm.
Reference Subscriptions All inputs have several sub-attributes to represent their data. The local (default) value and the reference pointer fields are configurable. The working value is always retrieved by following the reference pointer. The following three cases apply to input references:
1. When a reference pointer is not specified, the pointer by default points to the local value. 2. Optimized subscriptions use the reference pointer to pick a value in the DPU database (local memory) eliminating the need to subscribe to the Software Backplane. This takes the same amount of processor time as retrieving a local value. 3. Unoptimized subscriptions use the pointer to pick a value from a location, which must be interpreted. These would include points outside the DPMS, references to attributes of a different type, some status type attributes that are not stored, and sub-attributes of input attributes. Values by unoptimized subscriptions may not update every scan during periods of high DPU activity. 2.7 Configuration Tools
maxDNA Configuration Tools consist of maxTOOLS and maxVUE Graphical Configurator. They are the software elements used to configure, edit and maintain the Distributed Processing Units (DPU4E) in a system. These tools can run in any maxSTATION. They can configure the modulating/binary control strategies, the DPU database, sequence of events reporting, alarm types and set points, loop execution times, I/O card, bus, termination interface, and maxNET interface in a DPU.
Alarm Management One major problem faced by operators is an alarm flood during emergencies. As a result, important alarms may not be accorded the attention/priority they deserve. The alarm management function has to: • Prioritise Alarms with degree of importance • Filter out alarms that do not add any value to operator decision-making. • Find out the actual cause of the alarm as quickly as possible • Eliminate multiple possibilities to arrive at the root cause • Validate the diagnosis with correlated parameter values • Present the operator with a prioritised set of recovery options
maxVUE reports all alarms quickly and clearly. Its alarm management features are: • An alarm list with the top alarms upto 40 • Single keystroke alarm acknowledge or silence • 10,000 entry Alarm Summary display • 8,000 process alarms and 500 hardware alarms • Point and hierarchical alarm annunciator displays • Alarm defeat and restore • Automatic alarm cutouts to prevent nuisance alarms • Programmable tone for each group/ priority of alarms • Natural language queries to filter data
System (Diagnostic) Alarms • Station Alarms – Related to maxSTATIONs or RPUs (DPU or I/O) • Network Alarms – Related to maxNET Process Alarms • Limit Alarms – For parameters falling above/ below preset values • Status Alarms – For abnormalities in process
Operator Alarm Displays Alarm summary display: • Displays filtered or unfiltered alarms (max. 10,000) • Alarm filtering by hierarchical group and/or type, acknowledged and severity Alarm list: • Displays most recent acknowledged / un-acknowledged alarms • Default size is 5 alarms, but configurable from 1 to 40 • Alarm filtering by HID. 3
New Concepts Covered 3.1 Server less system with software backplane concept 3.2 Application of Ethernet for industrial networking in place of proprietary protocols. 3.3 A small range of hardware to realize a complex control system. 3.4 Simple PC based applications for programming and user interface.
New Trends / Practices
4.1 New control room design incorporating workstations and Large view screens enable operators view on different plant mimics from a single location. Due to integrated approach using same platform, operators need not move around to access control to different plant areas. 4.2 As the complete control realization like olcs, clcs etc are realized using software algorithms in DPUs, variety of electronic hardware is limited. Electronic hardware, other than DPUS, are used only for signal acquisition and conversion to digital. 4.3 Application programs use windows based software. Hence it is easier to learn and customize. 4.4 Getting data from different PLCs and other dcs if used are easily done with OPC compliance. 4.5 Integration of complete plant data including distant offsites like coal handling plant, CW pump house, switchyard are possible as plane wide networks can do this job. Unit networks can be kept out of interference by using gateways and firewall. 4.6 As alarm and annunciation systems are software based and hence are not limited by designed number of windows, customization becomes easier and additional hardware is not needed.
5 Application of learning 5.1 Self The knowledge gained in this training complements hand on working experience gained during commissioning of unit 7 Ramagundam. Hand on training exercises can be used to make proper procedure to implement certain changes to DPUs and application software. 5.2 Section /’ Dept: The learning of this training can be applied to find solution to plant problems and maxDNA is finding increasing applications in BHEL supplied units.. 5.3 Any other Deptt.of NTPC System knowledge will help in implementing interfaces to mechanical and electrical systems as one is aware of the design limits. 5.4 Company Level As BHEL is expected to supply and support maxDNA system for boiler and turbine controls and balance of plant were required well into the future, it is certain that the knowledge gained would be useful to iron out problems at commissioning stage and for following better maintenance practices. 6 Adoptable practices in NTPC 6.1 In Dept / section 1. As complete logics is in the form of software, latest software including modifications done up to the backup date shall be clearly marked and stored properly. 6.2 In any other Deptt/section Nil 6.3 Company level 1. Latest updates or patches released by Metso automation addressing any noticed problem should be obtained and system upgraded.