4.13
DCS: Operator’s Graphics T. L. BLEVINS, M. NIXON
Distributed control display for an indicator, controller, recorder or alarm point, usually for a video display.
(2005)
Flow sheet symbol
Types of Software Products:
A. Graphic Symbol Library B. Graphic Display Application
Partial List of Suppliers:
ABB (A,B) (www.abb.com) Emerson (A,B) (www.EasyDeltav.com) ESA Technology (B) (www.esa.int) GE Fanuc Automation (B) (www.faunc.com) Honeywell (A,B) (www.honeywell.com) ICONICS (A,B) (www.iconics.com) Invensys (A,B) (www.invensys.com) Kessler-Ellis Products (B) (www.kep.com) National Instruments (A,B) (www.ni.com) Nematron (A,B) (www.Nematron.com) OMRON Electronics (B) (www.omron.com) Reichard Software (A) (www.reichard.com) Rockwell (A,B) (www.rockwell.com) Schneider Electric (B) (www.Schneider.fr) Siemens (A,B) (www.siemens.com) XYCOM Automation (B) (www.xycom.com) Yokogawa (A,B) (www.yokogawa.com/us)
INTRODUCTION The operator’s workstation is the area where operators follow the process and, if assisted by fast and accurate translation of raw data into useful animations, trends, and patterns, can make the required decisions and take the correct actions. As was shown in Figures 4.2d and 4.2e in Section 4.2, one continuously attended operator console is usually dedicated to each section of the plant. The operator’s console includes one or more cathode ray tube (CRT)/liquid crystal display (LCD) monitors (described in Section 4.5), a standard or custom keyboard, a sound card, speakers, and a pointing device such as a mouse, trackball, or touch screen. This operator interface either replaces, or in case of upgrading of existing plants (Figure 4.3f in Section 4.3) supplements, the control room panel, which was/is filled with single-case analog controllers, meters, and digital indicators. In addition, the operator interface also replaces the previously panel-mounted start/stop pushbuttons and status indications, chart recorders, annunciators, and subsystem interfaces. In the early DCS systems, because of processor and memory limitations and because of lack of software, the operator interface displays consisted only of preformatted faceplates that provided measurement, alarm, and control. In
modern DCS the faceplate-type displays have been replaced by graphic displays. From the console the operators respond to alarms, adjust the operation of the process by changing set points or other parameters, “zoom in” on particular portions of the process for further details, and utilize specialized batch, advanced control, or business applications. Here, the hardware and functions of the operator console are discussed first, followed by a more detailed description of the operator’s graphics including both static and dynamic ones.
OPERATOR CONSOLE EQUIPMENT The operator console is usually an Intel processor-based workstation with single or dual 19-in. (475-mm) or 21-in. (525-mm) monitors. Memory requirements vary from 256 Mbyte to 1 Gbyte or greater. Hard disks can be either SCSI or IDE and range from 10 to hundreds of Gbytes. Peripherals include the two-button mouse, track ball, or touch screen with full duplex audio built into the motherboard. The allowable environmental operating ranges for the consoles are temperature 10 to 35°C (50 to 95°F), relative humidity 8 to 80% (noncondensing), vibration 0.25 G at 3 to 300 Hz for 727
© 2006 by Béla Lipták
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FIG. 4.13a Standard workstation hardware includes a monitor, CPU, keyboard, mouse, and speakers.
a maximum of 15 minutes. A typical operator station is illustrated in Figure 4.13a. Video Display The process monitor, sometimes referred to as the operator’s window into the process, is usually a 19-in. (475-mm) or 21-in. (525-mm) diagonal, multicolor CRT or LCD display. Some DCS systems offer smaller, mono-color screens for remote or dedicated functions. A few suppliers offer 25-in. (625-mm) diagonal screens for wall-mounted display, which are observable from the working area of the control room. The more common 19-in. (475-mm) and 21-in. (525-mm) monitors are for tabletop or console mounting. Most suppliers depend on visible cursor control to define screen areas; some use light pens. Touch-sensitive screens (Section 4.22) are quite common. They give the operator the ability to call up, for example, a detail from a larger graphic display by touching the portion of the screen where the corresponding process is located. One type of touch-sensitive screen uses a grid of conductive material that changes circuit capacitance when a crossing pair is touched. The material is embedded in a sandwich of transparent plastic. Another uses a grid of infrared light beams. Touching the screen breaks two crossing beams and triggers an appropriate response. Flat tubes are seldom used because of cost and resolution limitations. Similarly, standard distributed control systems do not accept voice commands or talk back to the operator. The technology exists for both, and at the present rate of technological change, these features will be soon available. The most difficult task at the console-based operations center is to effectively display on a limited screen area a com-
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FIG. 4.13b Graphic display providing an overview of a unit operation in the plant.
plex plant operation, monitored by hundreds if not thousands of sensors. This task is made more difficult by the fact that a human being is capable of assimilating only a limited amount of information at one time. Because of these considerations there is a need for both “bird’s-eye view” type overview displays, and for more details as contained in equipment graphic displays (Figure 4.13b). These displays tend to emulate the graphic panel of the traditional control room. If the operator needs additional information concerning the operation of a particular control loop, detailed faceplate displays are also available (Figure 4.13h). Other displays provide graphs, trends, and information on dynamic responses. Most importantly, such features as hot links allow the operator to “zoom in” on specific problem areas by drilling into detailed information that concerns only that area. Although providing useful displays for operators is a common goal of all DCS manufacturers, the solutions provided vary. Some suppliers give more emphasis to the keyboard in moving among the displays, effected by the use of dedicated function keys, addresses based on instrument tag numbers, addressing by group numbers, and function keys that are display dependent. Display-dependent function keys relate directly to the display on the video screen: depressing the key selects the associated screen segment and expands its information content in the next display. Other techniques used in obtaining this kind of telescoping effect can include the use of auxiliary cursor positioning (mouse), touch-sensitive screens, light pens, panand-zoom joysticks, and some other more advanced and less developed techniques, such as voice actuation. Keyboards Both standard and custom-made keyboards are used. Standard keyboards tend to sit on a table top. Custom keyboards
4.13 DCS: Operator’s Graphics
are often incorporated into the monitor housing or connected to the operator station by cable. The keys may be movable pushbuttons or they may be printed squares on a flexible membrane. The membrane-type keyboard is familiar to users of microwave ovens and pocket calculators. It has a cost advantage, besides permitting the design of imaginative keyboard layouts. The switches operated by the keys may be sealed reed switches, Hall-effect switches that are operated by actuating a magnetically energized semiconductor, or capacitative switches that are operated by the motion of a plate at the end of a plunger, which increases the capacitative coupling between two other plates. The membrane-type switch has a flexible, hermetically sealed covering. When the pattern of a key printed on the membrane is pressed, a conductive elastic sheet is pushed through an opening under the key picture, making contact with another conductive sheet beneath it. Some custom keyboards are implemented as a touch screen/monitor combination. This approach provides considerable flexibility in arranging the key layout, choosing which keys to automate or script, and support. Usually a fourth display is dedicated for this style of usage. Some keyboards use special function keys, which are programmable by the user. Others use a conventional typewriter keyboard combined with blocks of special-function keys whose purpose is predefined. Table 4.13c lists the functions that are commonly provided by keyboard keys.
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TABLE 4.13c Some of the Typical Key Functions Provided on DCS Keyboards Standard typewriter keyboard: Numberpad: 0–9, + and – Cursor control: up, down, left, right, home Cluster Alarm Acknowledge Defeat Restore Trending Trend time space Increase Decrease Range limit adjust Increase Decrease Mode select Automatic Manual Cascade Computer Direct input keys (input number keyed from keypad) Set point
Peripheral Devices Operator stations can be customized by adding extra memory, disk drives, networking cards, monitors, printers, and in some cases, backup devices. Whereas in the past printers were standard accessories, today they also store events in structured or relational databases to provide better reports, responses to queries, and analysis. Some government agencies, such the Food and Drug Administration (FDA), require the storing and inclusion of all operator actions in the batch end report.
Output Bias Ratio Set-point trim—slow and fast entry Raise Lower Output trim—slow and fast entry Raise Lower Logic
REMOTE AND WEB-BASED STATIONS
On, Raise, Start, Reset Off, Lower, Stop, Reverse
A number of vendors now offer remote access into their process as well as access to remote systems. The approaches seem to have been standardized; the two prominent ones are referred to by some suppliers as remote clients and Web pages. Remote Clients Remote Client access supports terminal services or remote desktop functionality. This capability allows full function operator workstations to be located remotely from the DCS. If it is used by engineers, they can operate and troubleshoot the DCS from their desktops with a direct local area network (LAN) connection or from remote locations using any of a
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Overview select Detail select Special function keys
variety of communications methods, including dial-up modems and virtual private network (VPN) connections. This capability is illustrated in Figure 4.13d. The remote client is made up of two hardware components—a client computer and a server computer. The server computer provides information to the remote clients. The client computer can be any Windows-based computer or thin-client hardware capable of running the remote desktop
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Wireless clients LAN client
Plant LAN
Remote server (ProfessionalPLUS or operator station node)
Modem clients
FIG. 4.13d The control and access capability of the operator workstation can be made available remotely by wired or wireless means.
connection software. Operator station software is not installed in this computer. Web Pages The widespread use and acceptance of the Web has led a number of vendors to fully integrate and support Web-style interfaces. Although security remains the key issue in this approach, at least one of the vendors, Honeywell, appears to have gone to great lengths to secure its Web services infrastructure. Web pages and Web services offer a number of advantages. They include the ability to integrate more enterprise application content and make that content available to many users on their local or remote desktops. Examples include monitoring and analysis of process conditions, performance indicators, and alerts from devices and equipment. The use of Web pages is illustrated in Figure 4.13e.
FIG. 4.13e Example of a Web-style interface, the use of which is supported by some DCS suppliers. These displays can monitor process conditions and alarms and can also provide multivariable trend recordings.
be unique for each plant. The control system manufacturer does provide some tools and some guidance in the development of the graphic displays, but the actual work is usually done by the design engineering firm or the user. The characteristics of the graphics systems vary with the needs of the users, but they all have to meet some basic requirements: •
OPERATOR GRAPHICS A graphic operator interface shows the piping, instrumentation, and other equipment that is part of a unit operation of the process. The primary advantage of such an approach is that more information can be provided to the operator. However, the effectiveness of such interfaces depends a great deal on the accuracy and completeness of the graphic displays. Standardized display packages cannot provide that accuracy, while custom graphics require substantial investments of time from both the user and the vendor. Modern distributed control systems include a variety of standard tools that can be used to create graphic operator displays. However, since the process equipment and associated field devices are unique to each plant and because most plants develop their own standard symbols and color schemes, the development of the graphic interface tends to
© 2006 by Béla Lipták
•
The operator graphics must be highly reliable because process control operators cannot control the “process” without them. Their characteristics include: • Must always be available. In many cases, the application must be available for long periods of time (e.g., weeks, months, even years) without unplanned disruptions. • Must be interacting. Operator must always have the opportunity to “move on” to other displays and to get predictable responses to new directives even when previous requests take “too long” to complete or “everything is changing” due to a plant upset. • Must be mistake-resistant. Repeatable behaviors and user interaction features have to be provided to help reduce the possibility of high-cost “human errors,” especially in high-stress situations. The graphics should provide extremely responsive interactions and fast call-up of process and historical information. This means that even large user-configured displays should be updated with live data from the DCS system within 1 second.
4.13 DCS: Operator’s Graphics
• •
•
•
•
•
•
The updating of data points, alarms, history, and dynamic graphic objects on the displays should occur in real time. The graphics should be suited for a dedicated (kioskstyle) operator environment and be resistant to programs or data on the workstation being damaged by users or people gaining access to unintended applications. The degree of restriction is usually user configurable so that the user can decide on access to the workstation. The graphics should interface with a wide range of user interface hardware features: • Two-, three-, or four-monitor video configurations • 4:3 (PC format) and 16:9 (HDTV format) aspect ratio monitors • Mouse + keyboard operation • Touch-screen operation • In newer systems, Tablet PC and PDA form factors and user input techniques The display graphics should provide the means for integration of operator tools/applications (e.g., batch, diagnostics, history viewing) with user-configurable displays (and user display logic) and also easy access to information related to display elements. These systems usually also provide easy access to auxiliary information sources (e.g., video feeds) and collaboration technologies (e.g., e-mail and instant messaging). The graphics should minimize the requirement for the operator to spend time in managing the windows and should allow the use of data sources not specifically engineered for use by the particular display. The display graphics must be provided with integrated user security and authentication facilities to support fast user switching and multi-user authentication for electronic signature requirements. The displays should provide a platform for improved information capture and analysis for operations staff. This usually includes features such as snapshot logs and the analyzing of alarm floods and history.
TYPES OF DISPLAYS The operator station in the central control room functions somewhat like the cockpit of an airplane, where the pilot sits and observes all the information relevant to the performance of the plane. The operator of a DCS system depends on the video screen of the CRT/LCD for plant information. Because the preparation of the various graphic and faceplate displays for a particular DCS application is both expensive and time consuming, it is important that the responsibility for their preparation be clearly resolved before the purchase order is issued. Each supplier has its own complement of lists, menus, and libraries (including measurement units and messages), which might include: • •
Graphic displays Detail displays
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• • • • • • •
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Faceplates Alarm summary displays Event summary display Trend displays Loop tuning displays Diagnostic displays Standard reports
The operator interface most often consists of overview, detail, faceplate, and trend displays. These will be discussed next. Overview Graphic Displays The graphic display of the whole plant provides a graphical and logical representation of the process, which makes it easier for operators to visualize what is happening. Overview displays are graphical displays with a lot of information to provide the operator with a “bird’s eye view” of the process. Such an overview display, as in Figure 4.13b, shows a section of the plant, with abnormal conditions animated (e.g., blinking) and/or colored (red). Additional animations are often provided to make the display more representative of the process. For example, a tank may be in the process of being filled, the agitator might be operating, etc. The operator, looking at an overview display, can see at a glance the condition of all the loops and can quickly spot a process variable or piece of equipment that is out of control. The operator can also note trends or recognize patterns, even prior to the full development of their consequences. On/off status can also be shown on an overview display. Discrete conditions (an open or closed switch, for example) can be shown as the presence or absence of a bar rising from the reference line. Sequential events can be displayed by displaying messages that change with the advance of the sequence. If the overview display indicates an alarm condition the operator can, with a single keyboard stroke, easily call up a more detailed graphic display which shows the active alarm. If the operator wants still more detailed information, another keystroke can often be used to call up a faceplate and detailed display of the loop that generated the alarm. Graphic Displays Graphics are valuable training tools and help the operator in following plant conditions when a number of variables are changing. The graphic display capability of a DCS system allows for the creation of both overview and more detailed graphic displays. Figure 4.13b illustrates the graphic display of a process that consists of three tanks. The graphic contains both process and control information, which is continuously updated in real time. On such a graphic, a pipeline downstream of a valve, for example, can become filled with color when the valve is opened or the symbol of the value can change color, say from black, when closed to green, which can indicate an open condition.
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Some graphic displays are also capable of showing movement. For example, when liquid is flowing in a pipeline, when solids are traveling on a belt, when agitators are turning, or when fuel is burning in a combustion process, the associated movements are dynamically displayed. Obviously, this capability adds to both the cost and to the information content of the display. Faceplate with Detailed Display The detailed display is usually specific to a single loop or control function. Figure 4.13h illustrates a typical controller faceplate display. The bar graph in the faceplate display can show the controlled process variable, the set point, and the output. The transmitters or other sources from which these signals are received are also listed on the screen. The display is identified with the tag number of the associated instrument; this tag number is also used in the DCS software to define the function. The tag number is added, using the keyboard like a typewriter to “fill in the blanks.” The configuration of a function is done by moving a cursor to locations on the screen where values are to be entered and typing in the values on the keyboard. In order to avoid errors or startup delays, it is advisable to make the preparation of the various graphic displays part of the DCS system supplier’s scope. Trend Displays Analog strip chart recorders have been replaced by trend displays in DCS systems. They display the past values of the recorded process variable over a period of time. Some detailed graphic displays (see Figure 4.13e) include a real-time trend graph of the process variable covering the selectable period of the last 90 seconds, 1 hour, or 24 hours. In some displays, several trend graphs can be displayed at once, allowing comparison of the history of several variables. One supplier can accommodate up to four trends graphs in a single display. Figure 4.13e also shows the trend display of several variables. This information is valuable to, for example, a foreman coming on shift who, by looking at these trends, can observe the recent patterns of operating history. It is also valuable to an operator after an upset has occurred because such trend recordings can help determine which condition was the cause and which were the consequences of an upset. Trends can also display historical data records. This allows the operator to go back in time to find patterns or conditions that might have caused similar previous upsets. STATIC GRAPHIC COMPONENTS ANSI/ISA-S5.5-1985 is an American National Standard for Graphic Symbols for Process Displays. The stated purpose of this standard is to establish a system of graphic symbols for displays that are used by plant operators in the area of process measurement and control.
© 2006 by Béla Lipták
The goal of such standardization is to help operators comprehend the information that is conveyed through the displays and to provide uniformity throughout the process industries. The benefits of such standardization are a reduction in operator errors, faster training, and more accurate presentation of control systems. This standard is followed by many companies and is suitable for use in numerous industries. However, the standard’s two-dimensional line drawings are a mismatch with current commercial workstation technology, where some of the graphic displays are three-dimensional. Faster computers with graphics card accelerators and vector graphics are supported by most DCS vendors. Highdefinition visual display units, VDUs, are commonly available based on CRT or LCD technology that support 800 × 600 to 2048 × 1536 resolution. Object-oriented libraries or GDI software allow more complete three-dimensional representations of the process equipment. Modern DCS systems include a graphic display editor and a comprehensive library of prebuilt display objects with professionally drawn three-dimensional representations of process equipment including pumps, valves, meters, piping, tanks, and other graphic objects. Also, some systems may offer the capability to import graphics from a number of different sources including AutoCAD and Windows metafiles such as Visio vector drawings, as well as Windows Bitmap (.bmp) and Joint Photographic Experts Group (.jpg) image formats. These components may be used to create a realistic representation of the process with added dynamic information. An operator display created by using a library of three-dimensional components is illustrated in Figure 4.13f.
DYNAMIC ELEMENTS If users decides to prepare the graphics on their own, detailed familiarity is required not only with the capabilities of the various DCS suppliers, but also with their software and the language they use, which might include such terms as “dynamos,” “aliases,” and “animation.” Some of these terms will be discussed below. Predefined objects such as knobs, dials, slide bars, and buttons are standard parts of any DCS graphic tool set and can be dynamically linked to information within the control system. Programmers call the workhorse of this linking process the dynamo (which has nothing to do with its “noncomputerize” meaning, the electric generator). The dynamo allows a particular field on the faceplate to be linked with a real-time reading and/or color that describes the state of the parameter associated with that field. In other words, “dynamo” in the language of the noncomputerese means the tool that is used to convert a field on a faceplate into a dynamic one. A library of custom dynamos is typically provided by the DCS supplier; it can be used to access the actual real-time values of measurements, calculations, analog and control components, etc. Often these preengineered dynamos can be
4.13 DCS: Operator’s Graphics
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FIG. 4.13f Some DCS systems offer the capability to import graphics, from which the experienced user can build the type of graphic display shown here.
customized to fit the specific needs and standard practices of the particular plant. Dynamos Standard dynamos typically include the key parameters associated with measurement and control functions. For example, a dynamo used to display a control loop may only display the controlled process variable, the set point, and the controller output. Therefore, the engineering units, for example, have to be added by the help of dynamos. Process alarms associated with control loops can be shown in the dynamo by color change, such as changing the background color behind a number representing the value of a process variable. Another use of color change can be to indicate that a loop is not in its designed/normal mode of operation. The ANSI/ISAS5.5-1985 standard provides general guidelines for the use of colors in displays. Red, for example, is reserved to indicate an emergency situation such as the stopping of a motor or the actuation of a highest priority alarm. The predefined dynamos provided with a control system conform to this standard. However, these guidelines may not match the traditions and past practices of the plant. In such cases, the colors used in dynamo templates can be modified to conform to the plant’s standard. An example of a dynamo is illustrated in Figure 4.13g. When the operator accesses a dynamo, a faceplate may be automatically presented providing further information on the parameter shown. For example, when a dynamo associated with a control loop is accessed, the faceplate presented
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to the operator may be used to modify the mode or change a set point or output. In addition, the capability may be provided to access further information, such as loop tuning, by selecting a detail display reference. Parameters in a detail display, which can be changed by the operator, are determined by the system security. As shown in Figure 4.13g, in some designs, not all the parameter values are displayed all the time; instead, it is necessary for the operator to sequentially obtain them (by clicking) on a parameterby-parameter basis. An example of a faceplate display with the associated detail display generated by accessing a control loop dynamo is shown in Figure 4.13h. Just about any property in a display can be converted to a dynamic element and animated. A list of the more commonly used dynamic behaviors are: • • • • • • • • • • • • • • •
Text Visibility Scale Position Rotation Skew Enabled, disabled Stroke (pen size) Fill color Stroke color Gradient (both linear and radial) Font Font size Filter Images
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This is the PV value of the loop module in yellow.
The background color of this field changes from invisible to orange or red if the PV status becomes uncertain or bad, respectively. Clicking this object brings up the faceplate.
This is the SP value of the loop module in white.
The background color of this field changes from invisible to orange or red if the SP status becomes uncertain or bad, respectively. This is a numeric representation of the OUT_READBACK value. This can be either Implied Output Position or Actual (if a wired IO_READBACK is available).
DATA
The background color of this box changes from black to orange or red if the OUT put status becomes uncertain or bad, respectively.
The background color of this object flashes the priority color of a new alarm for the loop. After acknowledgement, the color no longer flashes. The basic function is to draw attention to the module so that the operator opens the loop faceplate and possibly the detail display. This field displays the actual mode of the loop in yellow if the actual mode of the loop is something other than the normal mode. Otherwise, nothing is displayed.
FIG. 4.13g As can be seen from this example, the “dynamo” allows the programmer or the operator to link a particular field in the faceplate with a real-time reading and/or color that describes the state of the variable or parameter that is associated with that field.
Aliases In order to speed up the tedious work involved in designing displays, some DCS manufacturers use “aliases.” These software tools allow the designer to reuse previously designed displays or display segments and thereby eliminate the need for complete rebuilding of the displays for applications that are similar but are connected to different I/Os. If the DCS system supports the use of aliases in the definition of similar pieces of equipment, the dynamic display
components are usually designed to support dynamic referencing based on the piece of equipment selected for display. In such cases, preconfigured aliases and attributes are used in place of object tag or graphical attributes normally defined as part of the display object. Thus, aliasing improves flexibility and reusability because display objects can be connected to different I/O points and can represent different graphical attributes, appearances, and security. Such capability can eliminate the need to completely
FIG. 4.13h This example illustrates a faceplate that has been accessed (obtained) from a control dynamo.
© 2006 by Béla Lipták
4.13 DCS: Operator’s Graphics
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Module: MLMOD //MLMOD/OUT.CV
0.00 100.00
//MLMOD/GAIN.CV
Status:
Good cascade
DvText textFloat= Safe Enter
75.00
75.00
Limit state:
Limited constant
FIG. 4.13i An example of aliases used for a graphic element.
rebuild similar display objects. An example aliased substitution is shown in Figure 4.13i. Another way to improve the reusability of displays, faceplates, dynamos, and similar equipment is through the use of class-based displays. With this technique the display designer can develop displays with dynamic or aliased references. For example, the user could base the references in a display against library- or class-based items (e.g., a Phase Class in a batch configuration). When the display is instantiated during runtime, the graphics engine would resolve references based on the object that the display is being opened against. Display Access The increased use of a mouse in the operator interface has changed the way operators accesses information within a
FIG. 4.13j Navigational items in operator displays.
© 2006 by Béla Lipták
graphic display. Displays are typically designed to support both horizontal (at the bottom of the display) and vertical (to the right of the display) toolbars. The control system typically provides default toolbars to support the following functions: • • • •
Time and date display Alarm list with direct access to the display required to acknowledge the alarm Navigation to alarm summary, main menu, system status, last display, page back and forward, and print Alarm acknowledge and silencing
Figure 4.13j illustrates the operator display of one DCS supplier, showing scroll bars and navigational items that can be used by the operator.
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Plant overview display Dynamo access
Previous/next selection
Area A display 1
Area A display 2
Predefined trend of key parameters in display
Area A display n
Area B display 1
Area B display m
Startup and shutdown procedure
FIG. 4.13k Example of the hierarchy for accessing information and trend for a display.
Using the page forward and page back feature of the toolbar, it is possible for an operator to access displays that contain information upstream or downstream of the displayed process. In addition, dynamos may be added for accessing another display. Through the use of these tools, it is possible to create a display hierarchy that allows, from an overview display, access to the key display in each process area. Within the process area, it is possible to pan through the displays using a page forward/backward toolbar. Also, using a dynamo for display access and trend window access, it is possible to provide the operator with startup/shutdown information and trends of key parameters in a display, as well as in-context documentation, as illustrated in Figure 4.13k. The graphics editor supported by the control system allows incorporation of animation into a graphic display. Using this capability, the static graphic component for process equipment may be modified to indicate the status of the equipment for example motor on or tripped. Also, animation may be used to represent dynamic data associated with the equipment such as showing the level of a tank using a filling technique or showing the status of an agitator by rotating the agitator to indicate that the agitator is on. In newer products, adding dynamics to the properties of controls (send-to-front, -back, send-forward, backward) are used to show different information in the display based on the state of the process operation. In some cases it is necessary to create a specialized display complete with user interface (UI) controls such as buttons, check boxes, or sliders. The user would also add behaviors to these specialized displays—the behaviors could be driven from parameters internal to the special display or from parameters in another display, the DCS, or some external source such as OPC. A designer creating such a display would in general keep all of the references unbound so that the specialized display could be activated in context from some other graphic item at run time. PROCESS PERFORMANCE MONITORING The graphic display capability may be used to create special displays, allowing easily monitoring of the status of critical
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equipment. Some examples of these types of applications are: • • • • •
First-out indication on a process shutdown Vibration monitoring Burner management Sootblower Safety system status
The associated displays are structured to summarize the information. In cases where moving equipment is involved, such as a sootblower, animation may be effective, allowing an operator to quickly access the operation. The calculation capability of most control systems is used to implement online calculation of operation cost, efficiency, and other performance indicators. This type of information may be easily incorporated into the operators’ graphic display so that they can use this information to improve the process operation. An example of such types of calculations for a lime kiln operation is shown in Figure 4.13l. PROCESS GRAPHIC DATA INTERFACES A variety of data sources may be integrated into the process display graphics. The data may be sourced internal to the DCS from the runtime, historians (continuous, batch, event), and alarm services. The data may also be sourced externally from OPC, XML files, or even a hypertext transfer protocol (HTTP) browser. Supporting both internal and external data sources allows the operator displays to be used for a wider range of functions. The ability to activate interfaces external to the operator graphics is a very powerful feature. Examples of this include calling up menus in context related to applications external to the graphics—for example, bringing up the menu to calibrate a device from the graphics system. This is illustrated in Figure 4.13m. In special cases, the information may need to be displayed in a manner that is not supported by the control system. For example, some control systems do not support three-dimensional plotting of matrix values as is required
4.13 DCS: Operator’s Graphics
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FIG 4.13l Process performance indicators incorporated into the operator’s graphic.
FIG. 4.13m An example of performing operations on the process shown in Figure 4.13f by activating various applications from the operator graphics.
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to show sheet gauging information. To address these special requirements, the graphics display may support terminal server client/server interface for accessing the subsystem. CONCLUSION The graphics capability of modern control systems allows construction of an effective operator interface. The graphic editors provided with the control systems are used to create custom graphic displays that represent the process equipment and the associated field measurements. Preengineered graphic components and dynamos are used to easily create the operator graphics. The display features may be used to create a display hierarchy that allows the operator to quickly access information in any part of the plant. Information from performance monitoring and from subsystems may be directly included in operator graphics or in some cases incorporated using terminal server technology. Bibliography Ancilotti, P., Buttazzo, G., Natale, M. D., and Spuri, M., “Design and Programming Tools for Time-Critical Applications,” Real-Time Systems, Vol. 14(3), pp. 251–267, 1998.
© 2006 by Béla Lipták
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