Key Topics
Inspect Tune Fuzzy Simulate Neural Predict Predict ProIntroduction to This Manual
The DeltaV Advanced Control manual contains information about DeltaV software advanced control capabilities. It includes detailed descriptions of the functions available with DeltaV Inspect, DeltaV Tune, DeltaV Fuzzy, DeltaV Simulate, and DeltaV Predict.
DeltaV Inspect allows you to examine the health of your control system, measurements, and actuators. This manual provides information
about DeltaV Inspect's features that support the analysis of I/O function blocks (that is, AI, AO, DI, DO, and PIN) and Control function blocks (that is, DC, FLC, MPC, PID, and Ratio) for the following conditions:
control performance based on Variability Index abnormal measurement or actuator status control utilization based on Block Mode downstream limited condition on control
DeltaV Tune allows PID and Fuzzy Logic Control (FLC) function blocks to be automatically tuned on demand using the relay
oscillation principle. It can be used to tune the control over a wide range of processes and addresses many of the requirements in a typical operating plant. This manual provides a description of how the process dynamics associated with a control loop are captured by DeltaV Tune. It also details how this information is used to tune your control loops.
DeltaV Fuzzy is an alternative to PID control that provides faster response and improved performance over standard PID control on most
loops. The Fuzzy Logic Control (FLC) function block is the basis for DeltaV Fuzzy. This manual describes the FLC function block principles and its standard operations. It also provides references to other sections pertaining to this block.
DeltaV Simulate allows you to configure a DeltaV System on your laptop or office PC. You can configure all of the features that are
supported by DeltaV software without having to use DeltaV hardware. Also, you can simulate the execution of the DeltaV Operate and control modules defined for your plant in your PC. Using the Control and I/O block simulation capability of DeltaV software and Fieldbus, you can either manually supply field measurement values and status or you can have them automatically provided by function blocks or applications that simulate the process.
DeltaV Predict implements model predictive control of small and medium-sized multivariable processes in DeltaV environments. You can
control interactive processes within measurable operating constraints while automatically accounting for process interaction and measurable disturbances. DeltaV Predict also allows you to easily address the numerous small and medium-sized multivariable processes (2x2, 3x3 or 8x8) that can benefit from MPC technology.
DeltaV PredictPro implements model predictive control of large multivariable processes in DeltaV environments. It allows you to define as
many as five control objectives for interactive processes within measurable operating constraints while automatically accounting for process interaction and measurable disturbances. With PredictPro you can easily address a wide variety of multivariable processes as large as 20x20 that can benefit from Model Predictive Control (MPC) technology.
DeltaV Neural is a collection of tools you use to implement neural networks in DeltaV environments. With DeltaV Neural you can create
virtual sensors to monitor and predict process parameters that are otherwise expensive, difficult, or impossible to measure directly. Neural networks are sometimes referred to as intelligent or software sensors.
DeltaV Inspect
Inside this topic
The ability to inspect control and measurement loops quickly is of primary importance to industrial applications. Poorly tuned loops and malfunctioning field devices can jeopardize product quality and, quite often, production or yield. DeltaV Inspect provides advanced process monitoring that allows under-performing loops and malfunctioning field devices to be identified instantly. By providing this advanced capability, DeltaV Inspect takes full advantage of the fieldbus block architecture supported in the DeltaV system. A Bad, Uncertain, or
Limited measurement, downstream limitations in control, and incorrect mode of operation are automatically determined based on block mode and status of block parameters. In addition, the Input/Output function blocks (AI, AO, DI, DO, and PIN) and Control function blocks (DC, FLC, MPC, PID, and Ratio) include two parameters that are provided to support performance monitoring. These parameters are updated automatically without any extra block configuration. Since most calculations required for performance monitoring are done in function blocks, this approach greatly simplifies DeltaV Inspect and reduces network traffic between controller and workstation.
DeltaV Inspect provides indices that quantify loop utilization, measurements with a Bad, Uncertain or Limited status, limitations in control action, and process variability. In addition, DeltaV Inspect shows the overall control performance and utilization.
DeltaV Inspect contains the following features:
Software design based on function blocks and fieldbus architecture
Innovative loop performance and loop utilization monitoring techniques (patent pending on these techniques) A server that runs automatically with default settings
Easy custom settings
Summary results presented in a graphical way (bargraph) for hour, shift, and day Easy access to detailed results for modules and blocks and device alerts
Guidance for improving performance An easy-to-use user interface
Complete integration with the DeltaV environment
From the user interface you can monitor the performance of the entire plant or any part of the plant of particular interest. To provide for use of Inspect data in other ways, DeltaV includes an Inspect function block and an Inspect dynamo. Use the function block to make the calculated performance data available for viewing, plotting, adding to history, and so on. Use the dynamo to provide easy access for operators to Inspect data.
Note When a module that contains an MPC block is downloaded, all inputs and outputs are assigned to the DeltaV Historian. Do not change
the default history collection settings of the MPC function block.
Reporting Loop Utilization and Performance
DeltaV Inspect consists of one server and multiple clients. The server is the central collection point of the information obtained from the DeltaV controllers. The server performs hour/shift/day calculations, compares the results of these calculations with limits you set to detect under-performing loops, and provides this information to clients for viewing upon request. Refer to the Setting Limits for more information. The clients (the Inspect application) can access information only through the server.
Selected function block parameters in the DeltaV controller (such as measurement status, back calculation input status, and mode) are
automatically reported to the DeltaV Inspect server. This server is located on the DeltaV ProfessionalPLUS station. The information resulting from the calculation in the server can be accessed through any DeltaV Inspect client.
Information Flow for DeltaV Inspect
The status and actual mode parameters used by DeltaV Inspect to calculate loop utilization, Limited condition, and Bad measurement usually do not change in value. Parameters are communicated to the server only when they change in value. Therefore, the communication load for reporting these parameters is usually very small.
When the DeltaV Inspect Server is initially placed online, the current state of all required parameters is reported to DeltaV Inspect by the DeltaV controller. From that point on, the status of the parameters is reported only if it changes in value.
Loop Performance Calculations
Refer to this topic if you are interested in how these calculations are performed. Otherwise, refer to the Using DeltaV Inspect topic. The DeltaV Inspect Server calculates Variability Index (VI) for I/O blocks (AI, AO, and PIN) and Control blocks (FLC, MPC, MPC Pro, PID, and Ratio). For Control blocks, the DeltaV Inspect Server calculates an overall control performance and control utilization. Through these calculations, you can better judge the performance of plant measurement and control. These calculated performance measurements are available at DeltaV workstations that support DeltaV Inspect clients. The DeltaV Inspect window identifies either I/O blocks, Control blocks, or measurements whose Variability Index and total standard deviation exceeds the configured limits. In Input/Output function blocks and Control function blocks, the total standard deviation and capability standard deviation are calculated. Based on these two parameter values reported to the server by the controller, Variability Index as well as overall control performance are calculated in the DeltaV Inspect Server at the workstation. To reduce computer resource requirements, the Variability Index and overall performance calculations are performed in the DeltaV workstation.
Variability Index is computed from the following formulas:
S is the sensitivity factor that makes calculations stable. The default value is 0.1% of the variable scale. Stot is the actual measured standard deviation.
Slq is the minimum standard deviation that can be achieved with feedback control, where Slq is defined as follows:
Scap is the estimated capability standard deviation (measurement of short-term variation) Finally, for Control blocks, overall control performance is as follows:
Performance = (100-Average VI for Control blocks)%
Utilization = Average Percent Time Control blocks were in Normal Mode%
To support the VI and performance calculations, the I/O function blocks (AI, AO, and PIN) and Control function blocks (FLC, MPC, MPC Pro, PID, and Ratio) in DeltaV controllers and fieldbus devices calculate Scap and Stot. Stot and Scap are visible parameters (STDEV and
STDEV_CAP respectively) of these function blocks. The block parameter STDEV_TIME determines the timeframe over which these calculations are performed.
Calculations in Function Blocks
The I/O function blocks (AI, AO, and PIN) and Control function blocks (FLC, MPC, MPC Pro, PID, and Ratio) in DeltaV controllers and fieldbus devices support the STDEV and STDEV_CAP parameters, Stot and Scap. These intermediate calculations are done each time one of these function blocks execute. After N executions of the function block (where N = 120) or two minutes (whichever is longest), the parameter values are updated.
The total standard deviation, Stot, is calculated using "moving time window computation" based on N=120 executions of the function block and the time horizon (in seconds) defined by STDEV_TIME as follows:
where:
WFstd = 120/((STDEV_TIME/module execution period) + 120)
Stot_old = Previously calculated value of Stot
The PV is used in the I/O block to calculate the mean values as follows based on N=30 executions of the function block and the time horizon defined by STDEV_TIME.
Where WFmean = 30/((STDEV_TIME/module execution period) + 30) = Previously calculated mean value
In Control blocks, either the working setpoint or PV is used, depending on the block mode. The capability standard deviation, Scap, is calculated as follows:
where:
Scap_old = Previously calculated value of Scap
Only the summing component associated with the mean absolute error (MAE) and moving range (MR) is computed at each execution of the function block. The parameter STDEV_TIME should be set to match the time response for the process (in seconds) and by default is set to zero.
Identification of Under-Performing Loops
The following block measurement and processing conditions are automatically identified by DeltaV Inspect based on block mode and parameter status:
Mode Incorrect - The actual mode of the block does not match the Normal mode configured for the block. This can be caused by the
Limited Control (Action) - BKCAL_IN status of the block is either high limited or low limited, indicating that a block downstream from the
control block has reached a setpoint or output limit. Such limitations can prevent the loop from achieving or maintaining setpoint. Limiting is detected through BKCAL_IN only if the block is wired to another block such as AO. If a PID block with direct I/O is used, limiting is
detected through BKCAL_OUT. The limited condition is suppressed if this block is not selected by the downstream block because the downstream block should be flagged for incorrect mode.
Uncertain Input - The status of the block process variable (PV parameter) is Bad, Uncertain or Limited. A sensor failure, miscalibration of
the measurement range, or measurement diagnostics have detected a condition that requires attention by maintenance.
Standard Deviation - Standard deviation is a measurement of the variance of a block's PV (or working setpoint, depending on the block's
mode). Standard deviation is presented as a percent of EU span.
The percent of the time that these conditions exist over an hour, a shift, or a day is computed for every block by the DeltaV Inspect Server and compared to a configured global limit for each condition. When one of these limits is exceeded, the associated module is displayed in the DeltaV Inspect window.
Identification of Malfunctioning Assets
The Inspect application monitors assets (devices) for the following device diagnostics values: Advisory Device Count
Maintenance Device Count Failed Device Count Comm Fail Device Count Total Device Count
The diagnostic values are sent to the Inspect block as totals for the time period. For the Now time frame, the value is 0 or 1. For all other time frames, the values is the total count of the time the value was true. For large systems, this will typically be the number of minutes in the time frame. However, for small systems where there are fewer than 60 modules enabled, there may be more than one read per minute. This is similar to how data is polled for other Inspect items.
These values are available to the Inspect application directly from assets that support PlantWeb rules (fieldbus devices, for example). No additional configuration is required. For other assets, use the Diagnostic function block to access asset diagnostic information and make it available to the Inspect application. Asset parameters that indicate device diagnostic information can be wired to the Diagnostic block directly or processed by other blocks first, if necessary.
When you use Diagnostic blocks it is important to give each block a unique name. It is recommended that you name the Diagnostic blocks the same as the asset the block refers to. Because the Asset page does not include the module name in which a Diagnostic block resides, this naming convention eliminates duplicate names and gives operators more meaningful information.
Using DeltaV Inspect
Inside this topicDeltaV Inspect does not require any configuration or setup. You can start using it immediately by clicking Start | DeltaV | Advanced
Control | DeltaV Inspect.
Before DeltaV Inspect will recognize any changes or downloads of modules to a controller, you must download the controller setup data.
Note The first time that you access DeltaV Inspect, the DeltaV Inspect window displays the number of modules active as 0 because, by
default, no areas are enabled for data collection. For more information on enabling areas, refer to the Selecting Items to Monitor topic. The following figure shows how the DeltaV Inspect window Overview page appears after enabling processing on the entire system.
DeltaV Inspect Interface
If you need to delete module assignments from controllers in your configuration the recommended way is: 1. View Assigned Modules for the controller.
2. Right click on the module and select Delete Assignment.
3. Right click on the module again and select Download | Delete From Controller. 4. Download Setup Data to the controller.
If you attempt to remove module assignments from your configuration by deleting the assignment to a controller, then performing a total download, you must download the controller twice (total download followed by Download | Setup Data) to prevent DeltaV Inspect from displaying modules that have not been completely removed from the controller. This additional download is necessary because of the way the system manages module assignments and deletions during the download process.
The DeltaV Inspect user interface consists of the hierarchy (tree diagram) and three pages: Overview, Control, and Asset.
Overview Page
The overview page, includes a summary of the active asset alerts and shows the blocks that have one or more abnormal conditions. Click View | Options and select the Display tab to select the pages (Overview, Control, and Asset) that you want to display. The Overview page contains the following sections:
Control Section
This section graphically shows the percent of downloaded modules containing blocks that have abnormal conditions. Note that the graph is scaled from 0 to 20%. You can see the percent value by double clicking on a bar in the graph. The value for that bar appears in a popup. The actual number of modules that have each of the abnormal conditions is at the right of the graph.
The Performance and Utilization values indicate proximity to ideal control and indicate whether control blocks were used as designed, respectively. The third value in this area appears if you have PROCESS_IN configured in an Inspect block.
Asset Alerts Section
This section graphically shows the percent of assets monitored at each of the four alert levels: Asset Failed, Maintenance Soon, Advisory, and Communications Failed. Note that the graph is scaled from 0 to 20%. You can see the percent value by double clicking on a bar in the graph. The value for that bar appears in a popup. The actual number of assets at each of the alert levels is at the right of the graph. The numbers include all devices (Fieldbus or not) that are monitored for maintenance state.
The information of interest is the worst currently active alert level for the monitored device. For example, a device may have multiple alert levels active at one time but only the highest level will be reflected in the overview. For Fieldbus devices, this alert information comes directly from the device's shadow block. For non-Fieldbus devices, add Diagnostic function blocks to modules to report device alerts.
Control Page
Click View | Options | Display and select Control to display the Control page.
The Control page contains five tabs that list either performance information for all modules or only for modules that have exceeded limits, depending on the setting you selected in the Filters area. The Summary tab shows an overview of the information. Only modules containing I/O function blocks (AI, AO, DI, DO, and PIN) and Control function blocks (DC, FLC, MPC, PID, and Ratio) appear in the Module Name list. The abnormal conditions that can be detected are abnormal Mode, Control, Input, and whether the limits for average Variability Index and Standard Deviation have been exceeded. Modules are listed in alphabetical order. (The Module Name list is in the upper part of the tab. The Block Name list is in the lower part and contains a list of the I/O and control blocks in the currently selected module.) If one or more blocks in a module has exceeded one of the limits, the associated problem is indicated by an icon in the Summary pane of the Module list. The default icon is but you can change the icon from the View menu.
For each block, the percent of time that the mode, control, or input was abnormal is shown as well as the average value of the Variability Index and the Standard Deviation for each block, expressed in percent of EU span. The global percent time limits for mode, control, input, and Variability Index are shown along with the individual block limits for Standard Deviation. Use this information to identify the particular block that causes the module to be included in the Module Name list as well as the percent of time that the condition was abnormal.
The remaining tabs show more detailed information for each of the abnormal condition types. For more information, refer to the online help for the Inspect application.
Asset Page
Click View | Options and select Asset to display the Asset page.
The Asset page provides a list of assets (field devices) that have abnormal alert conditions. Filter selections are available to present all assets, assets in alert only, or fieldbus devices in alert only. The timeframe is always Now for information shown. The Asset page lists the asset name (or the associated Diagnostic block name for non-fieldbus assets) and the active alert conditions, if any, for each device. Right clicking on a block or device opens a menu from which you can open the appropriate detail analysis application, if one exists. For example, selecting the Diagnostic block associated with a CSI monitored device presents On-Line Watch as a menu choice. If a Fisher-Rosemount fieldbus device is selected, then the choice to open AMS Device Manager software appears.
DeltaV Inspect monitors all I/O and Control blocks that are downloaded to any DeltaV plant areas that have been enabled through the DeltaV Inspect interface.
Note Inspect limits the number of modules it watches to 10,000. If you attempt to enable an area that would add enough blocks to exceed the
limit, the area is not enabled.
To enable and disable Inspect performance and utilization calculations for areas, process cells, and unit modules, use the hierarchical list at the left of the Inspect window.
Hierarchy Tree
For those modules that are contained within an area assigned to DeltaV Inspect, the software automatically includes all of the I/O function blocks (AI, AO, DI, DO, and PIN) and Control function blocks (DC, FLC, MPC, PID, and Ratio) as long as those modules have been downloaded to a DeltaV controller. As modules are added or deleted, DeltaV Inspect detects these changes. In other words, no module-level configuration is necessary for tags to be included in DeltaV Inspect.
To enable and disable Inspect performance and utilization calculations for individual modules and blocks, use the Module Name and Block Name lists. The following figure shows the Control page Summary tab of the Inspect window.
Modules and Blocks Area
Enable and disable performance calculations for individual blocks and modules by right clicking on a module or block name and selecting from the drop-down menu. Note that if you disable all the blocks in a module and have the Filters area Modules toggle set to Limit Exceeded Only, the module containing the blocks you disabled disappears from the Module Name list. To make it reappear, set the Modules toggle to All Modules.
Filtering Items to Monitor
The settings you make in the Filters area help determine what modules and blocks are included in the performance and utilization calculations. You can filter by time period, Block Types, and whether all modules or only modules in which one of the limits has been exceeded are included in the Module list in the DeltaV Inspect window.
Filters Dialog
There are two areas on the filters dialog: Control Filters and Asset Filters. Control Filters Area
The two pulldown lists are Time Frame and Time Window. The choices for Time Frame are Now, Current, and Previous. The choices for Time Window are Hour, Shift, and Day. If you select Now, the Time Window list is not available and Inspect uses the instantaneous
parameter values of the block to determine if a module is in the Module list. By combining selections in the two lists you can filter the Inspect data for the following time periods:
Current Hour Current Shift Current Day Previous Hour Previous Shift Previous Day
In the Block Types area, select one or more types of blocks to include in the DeltaV Inspect window.
In the Modules area, you can elect to have all modules shown in the Module list or only those modules that have at least one block that exceeds a limit (either for average variability or percent of time that the mode, control, or input was abnormal).
Asset Filters Area
In this area select whether you want to see all assets, only assets in alert, or only fieldbus devices in alert.
Setting Limits
Default limits are provided in the DeltaV Inspect configuration for Variability Index, Standard Deviation, incorrect mode, limited conditions, and bad or uncertain inputs. The default limit for Variability Index is 30 percent (30%). The default limit for Standard Deviation is by block and the default is three percent (3%) of the EU span. The default limits for incorrect mode, limited conditions, and bad or uncertain inputs are set at ten percent (10%). You can change these default values from the Block Name list.
The limits shown in the Block Name list for Incorrect Mode, Limited Control, Bad or Uncertain Input, and Variability Index apply to all blocks. If you have tune privileges you can change these limits. To set a limit, double-click the limit you want to change and modify it in its cell. You can also right-click the limit you want to edit and select Modify from the drop-down menu.
From a DeltaV Inspect client (the Inspect application), if you have tune privileges you can change the percent time limits and the variability index used to detect when blocks are not operating as expected for too long a time. The values for which you can set detection limits include:
The percent time control is Limited,
The percent time the block PV is Bad, Uncertain, or Limited, the Variability Index.
In addition, you can set the Standard Deviation Limit for each block. There are three ways to set this limit: Set an individual limit. The limit is set to the value you enter.
Set the limits of all blocks in the system that are of a particular type (Control, Input, Output). The limits are set to the value you enter. Adjust the limits of all blocks in the system that are of a particular type (Control, Input, Output) to their current Standard Deviation
value plus an offset that you specify. The limits are adjusted by the value you enter.
Note All limits (abnormal conditions or Standard Deviation Limits) are set or changed from the Inspect clients, but are stored in the server.
All clients use the same set of limits, regardless of which client set them. However, a changed limit is used by the clients, but not stored permanently, until a user with sufficient privilege updates the database. In this way, you can set or adjust limits temporarily, and if the changes are unsatisfactory, restore the original limits from the database.
If one or more limits have been changed but not updated to the database, a message appears in the Status Bar at the bottom of all Inspect clients. To save changes permanently in your database, click File | Update Database. To restore the previous limit values that you modified in the server, click File | Restore from Database. Note that these menu items are not available unless you have changed limits.
You can also enable and disable performance calculations for individual blocks and modules by right clicking on a module or block name and selecting from the drop-down menu. Note that if you disable all the blocks in a module and have the Filters area Modules toggle set to Limit Exceeded Only, the module containing the blocks you disabled disappears from the Module Name list. To make it reappear, set the Modules toggle to All Modules.
Defining Shift Times
Two, three, or four shifts can be defined. The shift time is used by the DeltaV Inspect Server in calculating and displaying shift and daily DeltaV Inspect summaries. To define shifts, click View | Options, select the number of shifts per day, and then select the time at which the first shift starts. DeltaV Inspect automatically calculates the starting time for the remaining shifts. For example, if you select 3 shifts and specify that the first shift starts at 8 a.m., DeltaV Inspect automatically sets the second shift to start at 4 p.m. and the third shift to start at midnight.
When you select either the Print icon or File | Print, a dialog appears from which you can print either an active module summary report or a detail report on the local workstation printer or the selected network printer. The active module summary report contains the Performance Index, Control Utilization, total number of active modules, and the number of modules with one or more blocks that is in an incorrect mode or has Limited Control, Uncertain input, or large variability. The detail report contains the Percent Time Abnormal, Average Standard
Deviation, and Average Variability Index for each I/O or Control block for the selected Time Frame.
Defining an Inspect Operator Interface
The DeltaV system includes two items you can use to create ways for operators to interact with Inspect: the Inspect function block and the Inspect dynamo. For information on configuring and using the Inspect function block, refer to the Inspect Function Block topic.
Use the Inspect dynamo in the DeltaV system to include Inspect performance and utilization calculation results in operator displays. When you insert the dynamo in a display, it prompts you for the tag of an Inspect block. The dynamo also shows the area over which the
calculations are made and a button operators can use to enable and disable the calculations for the area. The following figure shows how the Inspect dynamo appears in a display.
Inspect Dynamo
From the dynamo, an operator can enable or disable Inspect calculations for the area named in the dynamo. The two fields on the dynamo show the calculated performance and utilization for the modules in the area. The background color of these fields is invisible if the data status is good, orange for uncertain status, red for bad status, or magenta when data is not being communicated.
Variability Limits
Variability Index shows a control loop performance relative to the best possible performing loop (Minimum Variance Control Loop). In theory, a perfectly tuned loop has Variability Index close to zero. It should be noted, however, that minimum variance control is neither
achievable in real control loop nor desirable to achieve. At perfect minimum variance control, a control loop experiences excessive movement of the controller output and has a rather narrow stability margin. Variability Index close to one hundred percent (100%) indicates an
extremely poorly tuned loop. To achieve a compromise between as low as possible variability and reasonable loop stability margin, Variability Index of around ten percent (10%) should be satisfactory for most loops. Fine adjustment of Variability Index limits should be determined based on the loop performance when it is correctly tuned.
Similarly, Variability Index provided for input blocks can be used to judge relative stability of processing conditions. Variability Index that shows a dramatic increase indicates a change in process load disturbances. For Output blocks (for example, AO), large Variability Index indicates that the control loop adjusting the valve is tuned too tightly or that the loop is compensating for large process disturbances. Also, mechanical wear or stiction in a final control element can cause associated Variability Index to be have a high value.
Application Examples
The following information provides common examples to illustrate how some of DeltaV Inspect's key features can be used in an operating plant.
Loop Not in Normal Mode
A critical process input flow loop is designed to run normally in Cascade mode with its setpoint set by a composition loop (the loop's Normal mode element has been configured as Cascade). However, on the midnight shift, the operator changes this flow loop to Auto because of wide fluctuations in the setpoint. The next morning, the process engineer for the plant sees that DeltaV Inspect flagged the actual mode as being incorrect for more than one percent (1%) of the time. The process engineer can use this information to quickly determine that a problem existed in the primary loop tuning. By quickly identifying and resolving this problem, the process engineer can minimize any off-specification product that resulted from manual adjustment of this key flow.
Limited Output
An instrument technician for a power plant notices DeltaV Inspect showing the oil flow control loop as being limited in operation. The instrument technician finds that the setpoint for the oil header pressure control was below the design pressure, forcing the oil valve to go completely open under heavy load conditions. By adjusting the pressure back to its designed target, the oil valve can now meet its setpoint without going completely open.
Uncertain Input
DeltaV Inspect flags a key temperature measurement as Bad over one percent (1%) of the time over the last day. The instrument technician examines the transmitter calibration again and finds that the device was calibrated for too low of a temperature range. The instrument
technician resolves the problem by recalibrating the transmitter for the correct temperature range. Recalibrating the transmitter might improve the accuracy of the measurement. Any improvement in accuracy of the measurement also improves the process operation.
High Variability
During normal operation of the plant, a plant engineer sets all Variability Limits to the current value plus ten percent (10%). After a few weeks, he notices that DeltaV Inspect flagged a critical flow loop as having excessive variability. Upon further investigation, he finds that the valve positioner connection to the valve stem is loose and is causing the control loop to cycle severely. After fixing the valve positioner, Variability Index returns to its normal value.
Note The normal value for the Variability Index limit for a specific block varies with the associated process dynamics, normal disturbances,
and so on. Use DeltaV Inspect to detect when Variability Index increases dramatically from its normal value. Often, such an increase indicates a change in the process, measurement element, or control element that needs attention.
DeltaV Tune
Inside this topic
DeltaV Tune implements a relay oscillation principle. This principle is based on the patented Aström-Hägglund Algorithm for calculating the tuning parameters of a process control loop. Emerson Process Management has enhanced this algorithm with a patented technique for
identifying process deadtime.
During tuning, the output of the Proportional Integral Derivative (PID) or Fuzzy Logic Control (FLC) block that is selected for tuning is determined by a known function that acts as a relay with hysteresis. This relay provides two-state control and causes the process to oscillate with a small, controlled amplitude. Using the amplitude and the frequency of this oscillation, DeltaV Tune calculates the Ultimate Gain and Ultimate Period of the process. The controller settings are then computed based on the defined process parameters and selected process type. Optionally, tuning rules for modified Ziegler-Nichols, Lambda, or Internal Model Control can be selected in determining the best loop tuning. To check and allow further refinement of tuning, DeltaV Tune provides simulated loop response, robustness plotting, and robustness based tuning.
DeltaV Tune:
Uses a field-proven method implemented since 1986 in Fisher-Rosemount Systems' stand-alone DPR 900 controllers. Uses a patented tuning principle.
Is applicable to a wide range of processes because no specific model is assumed.
Can start tuning when a loop is in either a manual (Man, ROut) or automatic mode (Auto, Cas, RCas). Is suitable for both fast and slow processes.
Has an easy-to-use operator interface. Is integrated with the DeltaV environment.
May be used to tune PID blocks assigned to execute in fieldbus devices.
Provides a wide range of controller designs for various user needs (modified Ziegler-Nichols, Lambda, Internal Model Control). For information on how to use DeltaV Tune to tune PID and FLC blocks, refer to the Using DeltaV Tune topic.
Loop Tuning
Once a control loop is designed and configured to govern a specific process, it must be tuned. Making the necessary adjustments to provide for stable and responsive operation of the process is referred to as loop tuning.
If a loop is tuned for responses that are too slow, the process is stable but not responsive. If the loop is tuned for responses that are too fast, it can be very responsive, but it might overshoot and cycle around the setpoint (SP). The objective is to achieve a reasonably responsive and stable control loop.
The most common methods of loop tuning are calculated tuning and trial and error tuning. The calculated method involves computing the tuning values using known constants and algorithms. The trial and error method involves manually adjusting the tuning values until the process is stable. The calculated method is superior to the trial and error method because it requires a small number of cycles to achieve the desired results. If a process is slow, using the calculated method can be extremely advantageous to using the trial and error method.
The primary control blocks provided in DeltaV software are the PID and the FLC blocks. You can use DeltaV Tune with the PID block to calculate the proportional, integral, and derivative terms automatically for a particular process based on the process type and tuning rule you select. DeltaV Tune can automatically calculate the fuzzy scaling for error, change in error, and change in output to give the best response when you use the FLC block for control.
DeltaV Tune is distributed between the DeltaV workstation and the DeltaV controller. You can only initiate tuning if you have sufficient privilege at the DeltaV workstation being used to view and interact with DeltaV Tune. Time-critical features associated with the process identification are implemented in the function block. This approach allows the process dynamics to be captured precisely without introducing errors by communication delays. The portion of DeltaV Tune in the workstation supports viewing controller parameters and tuning
shown in the following manner:
Distribution of DeltaV Tune
In the process identification phase of tuning, the PID or FLC block actual mode switches to Local Override (LO). Once in LO mode, the operation of the loop's primary control algorithm is suspended, and the controller resident relay identification adjusts the control block output (OUT). The DeltaV workstation contains the tuning rules used to calculate the PID tuning (gain, reset, and rate) or FLC scaling factors. These newly calculated values are displayed at the DeltaV workstation, and you are given a choice to accept the new values, calculate different tuning values, or continue operating with the present tuning values.
Tuning System for Determining Process Dynamics
The above figure illustrates the tuning system for capturing process dynamics using the relay oscillation principle. During the identification procedure of loop tuning, the mode of the PID or FLC block changes to LO and the output is determined by a two-state (or relay) function. During this phase of tuning, the loop is under two-state control. As indicated previously, loops under two-state control exhibit slight oscillations. The amplitude of these oscillations defines the Ultimate Gain. The oscillation period defines the Ultimate Period. The Ultimate Gain (Ku) is defined by the following equation:
where
d - relay amplitude
a - amplitude of the oscillation of the process variable (PV)
Having identified the Ultimate Gain and the Ultimate Period, you can determine the controller PID settings using the modified Ziegler-Nichols rules. You can also determine the process deadtime based on the initial phase of the oscillation test. Based on a knowledge of the deadtime, Ultimate Gain, and Ultimate Period, DeltaV Tune can calculate the process time constant and static gain needed for model-based
tuning (Internal Model Control tuning and Lambda tuning) available in DeltaV Tune as options.
Tuning Period
The following figure illustrates a typical time plot of the relay output and the process variable (PV) during tuning. Note that the relay is triggered at the point when the PV passes through the SP.
The relay amplitude (d) is typically 3 to 10 percent of the controller output range. For a DeltaV control block, this corresponds to the percent change in OUT. The PV change (a) is largest during initialization (that is, during the first oscillation period). Typically, the PV change ranges from 1 to 3 percent of the PV range.
Relay Output and Process Output During Tuning
Oscillations must continue for at least one period after initialization. If more periods are used for tuning, the average amplitude of the oscillations is used to determine the Ultimate Gain. DeltaV Tune uses two tuning periods by default and defines the amplitude of the oscillations as the average amplitude.
During the oscillation periods after initialization (the tuning periods), relay switching is disabled at the start of each half period to increase the tuner's resistance to noise. The duration that the relay switching is disabled depends on the deadtime of the tuned loop, which is defined during the initialization period.
Relay Hysteresis
For very noisy processes, you can adjust the amount of relay hysteresis for additional noise protection. With hysteresis, the relay switches only if the PV passes through the SP by a specified amount.
Under stable conditions, the relationship of input and output can be expressed by the transfer function. Generally, a process transfer function can be represented by a magnitude (or amplitude) and an angle (or phase shift). When the frequency varies from 0 to infinity, the transfer function changes. The resulting curve is called the Nyquist curve. The following figure shows a typical Nyquist curve for a control loop at the tuning.
Example of a Nyquist Curve
where
N(a) is the describing function of the relay.
is the relay hysteresis.
d is the relay amplitude.
a is the amplitude of the oscillation of the process variable (PV). i is the imaginary component.
N(a) amplitude is considered an approximation for the Ultimate Gain. Note that with hysteresis, , N(a) is exactly the Ultimate Gain, as shown in the above formula.
However, with hysteresis, the frequency and gain determined by the oscillation are not exactly the Ultimate Period and the Ultimate Gain. As illustrated in the above figure, the hysteresis introduces an error in defining the critical point of the Nyquist curve.
To prevent the introduction of additional errors, only set the relay hysteresis when DeltaV Tune will be operating in an extremely noisy environment.
Using DeltaV Tune
Inside this topic
The DeltaV Tune window leads you through the steps used to tune a loop. This allows tuning to be completed quickly and with minimal input. The typical tuning procedure is performed in the following sequence:
1. Select the PID or FLC block to be tuned in Control Studio or DeltaV Explorer, right-click the block, and select Tune. You can also initiate tuning from the Start menu.
2. Identify the process dynamics. This is done automatically by the DeltaV Tune test initiated at your request. 3. Select the basis for tuning either by specifying the process type or the tuning rule to be used.
Before tuning a loop, the PV should be reasonably stable and near the SP. If the loop is not stable, the calculated control variables will be inconsistent and possibly inaccurate.
Note Before starting the tuning process, make sure that the loop is reasonably stabilized at the SP. Observe the noises and disturbances of the
system. If the controller output is constantly changing due to noise or disturbances, you might consider beginning tuning the loop from the Manual mode. This approach will provide you with better results.
If the loop you are tuning has an extremely high noise level, the tuning calculated by DeltaV Tune might be inconsistent. If the PV is stable but the controller output is constantly changing, your process loop might require noise protection.
If the PV and the controller output are stable, you can start tuning the loop as outlined in this section.
You can use DeltaV Tune if you have Tuning and Control keys assigned to your user account. If this is your first time using DeltaV Tune, you might want to use simulator modules for PID and FLC before using DeltaV Tune on a live process. For more details, refer to The Simulator Configuration topic.
Selecting Function Block to Tune
DeltaV Tune can be used with a PID or an FLC block. Tuning can be initiated from Control Studio, the DeltaV Explorer, the operator faceplate, or the Start menu.
To initiate DeltaV Tune from the DeltaV Explorer, select a module assigned to a controller or the specific block of a module. If you select at the module level, you must type in the block name at the first DeltaV Tune screen.
Alternatively, you can invoke DeltaV Tune from the Start menu as shown below:
After selecting DeltaV Tune, the DeltaV Tune window appears. If you request a particular block or module, it is shown as the Block Name in the Select loop to tune panel. Alternatively, you can select either Select Function Block or Open File and choose the block to be tuned. By selecting Open File, you can use a previously tuned block as the starting point for tuning this block again. If you select Open File, the last tuning settings and process dynamics for the associated block become the starting point for the tuning process. Once the block selection is complete, you can begin the process identification phase of DeltaV Tune.
Using DeltaV Tune with Fieldbus Devices
You can use DeltaV Tune with PID blocks executing in fieldbus devices as well as with PID and Fuzzy logic blocks assigned to execute in the controller.
You have several options on how to implement control options with fieldbus devices: You can assign all elements of the control loop to fieldbus devices.
You can assign the loop PID to the transmitter or the valve.
You can assign portions of the control loop, such as the PID, to the DeltaV controller and assign the remaining functions, such as AI and AO, to fieldbus devices.
There are several things that affect control performance when using fieldbus devices:
Function block execution, maximum response time for compel data minimum schedule spacing, and slot time depend on the device technology and design (depend on the device manufacturer).
Whether control is performed in the fieldbus device or control system.
The scheduling of block execution and communications on the Foundation fieldbus segment.
Macrocycle is the time for scheduled and unscheduled communications. Scheduled communications includes function block execution time and transfer time (minimum schedule spacing). Unscheduled (asynchronous) communications are for Client-Server types (Function Block Views, SP changes, and Device Alarms for example). A minimum time for unscheduled is added to determine the macrocycle time.
If you split control between fieldbus devices and the DeltaV controller the execution of the module in the controller is not synchronized with the function block execution in the fieldbus segments. This lack of synchronization introduces a variable delay in the control loop as great as the segment macrocycle. For example, a 1/2 second loop in which control is split can have as much as 1/2 second of additional variable delay. The added delay affects control loop tuning and can result in and increased variability in a fast control loop.
The recommended way to split control between fieldbus devices and the controller is to execute control loops in fieldbus devices when the process dynamics are fast, for example, liquid pressure or flow. For example, for better performance, implement a loop with an execution time of 1/2 second or less in a fieldbus device and limit the number of control loops to no more than two per H1 segment.
DeltaV Tune uses a hidden modifier to the PID block to capture process dynamics. In most manufacturer's fieldbus devices, this modifier is attached to a PID block in the controller that shadows the PID block in the device. You cannot see the PID block in the controller, or its hidden modifier.
All new Emerson fieldbus devices will include the hidden modifier in the PID block in the device. This eliminates errors introduced by communications delay or jitter and supports tuning of even the fastest loops. There are no changes to how the DeltaV Tune interface looks
and operates. The ability to tune loops running in fieldbus devices leads to reduced variability for fast process dynamics.
Identifying Process Dynamics
After you select a block for tuning, DeltaV Tune must identify the process dynamics associated with the control loop. Look at the Test Process panel on the left side of the DeltaV Tune window.
Process dynamics are determined automatically by DeltaV Tune. If the controlled parameter (PV) reflects an accumulation or imbalance between inlet and outlet flow, select the Integrating process. The percent change in the PID block output from its initial value is determined by the selected step size. A default step size of 3 percent is sufficient for most situations. For most processes, start tuning with a step size of 3 percent. If the gain of the loop is high or the process is integrating (not self-regulating), use 3 percent initially. Use a step size of 5 or 10 percent if tuning does not develop oscillations with a 3 percent step size. The tuning might not develop oscillations if the gain of the loop is extremely low or the loop has too much noise. However, a 10 percent step size is not recommended for integrated processes.
In some cases, process measurement is noisy or characterized by significant load disturbances. If such conditions exist, better results might be achieved by using relay hysteresis or by extending the length of testing.
If the process characteristics such as gain, time constants, noise, scaling, and so on seem out of the normal range, click the Default Process button to modify the tuner settings to better fit the process characteristics. Note that the Expected Process Response option is not supported for PID blocks running in fieldbus devices.
After checking these entries and making the appropriate changes, click Test to initiate testing of the process and identify process dynamics.
Caution Before starting the tuning process, make sure that the loop is reasonably stabilized at the SP. If the PV is not close to the SP, begin
tuning the loop from Manual mode.
After selecting Test, the PID block output adjusts from its initial value by the step size. You can stop testing at any time by clicking the Abort button. When testing is not active, you can change the target mode and the SP of the block from the Controller panel. You can change output when mode is in Manual.
When tuning a loop, the SP and output should not be at either end of their respective ranges. The output must be no lower than 10 percent of the range and no higher than 90 percent of the range or the oscillations will be affected.
The PV of a loop should be close to the SP when you begin tuning. DeltaV Tune checks the values for the SP and the PV before tuning the loop. If the deviation is too large, this indicates that the loop is not stable enough to begin the tuning process. The tuner waits until the SP-PV value is within the required limit.
If, under normal operations, either the SP is not close to the PV, the loop is influenced by disturbances, or a loop is in a transient condition, the tuning results will not be as accurate and consistent as those from properly stabilized loops.
If tuning proceeds properly, the state changes to an active state, and the control block actual mode changes to Local Override (LO). The time between each change in the block output depends on the process response time. For example, a change in the process input (block output) might not be immediately reflected because of process delay in the controlled parameter (block PV). Watch the Trend display area during the tuning process. If loop trend traces are not typical or tuning does not start, restore the initial loop conditions by clicking the Abort button. While testing is active, status is shown as Testing process in the Test Process panel. The progression of the testing is indicated by a bar graph showing percent completion, as shown in the following figure.
Once testing is successfully completed, the loop returns to the original mode and original output. The process dynamics that were identified are shown in process results for a self-regulating process, as shown in the following figure.
When Integrating process is selected, the process dynamics for an integrating process are displayed, as shown in the following figure.
The dynamic values displayed vary with the process controlled by this block. You can repeat the tuning procedure for the same loop by selecting Test again.
If abnormal conditions are detected during testing that might impact the accuracy with which the process dynamics can be identified, a warning or an error message is issued. When the detected condition prevents testing to be completed successfully, an error message is generated and tuning is stopped.
calculations based on the identified process dynamics. If testing did not complete successfully, an appropriate warning message is issued.
Establishing Loop Tuning
In the loop tuning phase for a PID block using the Normal selection, the following Tuning Calculation panel appears:
The Desired Response options are Normal, Slow, and Fast.
If an FLC block is being tuned, the Tuning Calculation panel displays the recommended scaling factors for the FLC block, as shown below:
response selected in this panel. When using the Normal setting, tuning calculations are performed by non-linear estimators. Non-linear estimators correct major deficiencies of Ziegler-Nichols tuning:
too short controller integral time for processes with small deadtime to time constant ratios excessive controller integral time for processes with a significant deadtime
excessive controller gain for processes with small deadtimes
You can modify the recommended tuning values by entering the values you want into the fields provided. To transfer these settings from the workstation to the PID or FLC block, select Update=> in the bottom of the panel. After selecting Update=>, the recommended settings are transferred to the block, and the new tuning values are displayed as the current settings. To restore the original settings, select Restore in the Controller panel.
The default process type for a PID block using the Normal selection is Typical - PI. This default is used for the initial tuning recommendation unless you change the process type. However, if this selection does not match the process, you must change the process type to one of the following selections: Typical - PID Temperature Gas Pressure Flow Liquid pressure Tight Level Deadtime dominant
After you change the selection, the recommended tuning is updated.
If the process is identified without messages, the results are displayed in the Process test results area. If the identified process deadtime is greater than a quarter of the time constant, you can improve loop performance by clicking Options | Expert.
If the identified process deadtime is greater than the time constant, select Deadtime dominant. If you have applied the Smith predictor in your control module (refer to the PID_DEADTIME Module Template topic), click Options | Expert and then select Lambda Smith Predictor in the Tuning Calculation panel.
The following information applies to PID function block tuning:
The loop response specifies the speed at which a control loop responds to process upsets and SP changes. The recommended proportional gain for a particular process changes depending on the loop response. The default setting of Normal gives moderate
response. By selecting Fast, the controller output change is greater and loop's response faster. Selecting Slow has the opposite effect. If, after determining the process characteristics, the process gain is less than .6 or greater than 2.5, model-based tuning is not
recommended.
If the Expert option is not selected, you are then using the modified Ziegler-Nichols tuning rules. This is the default selection and should be used as a first choice. However, if you find that the tuning results are not satisfactory, you can then click Options | Expert. If you select Use model-based tuning, you are then using one of the following: the Lambda PI tuning rules with a Lambda factor of 1.5
for Normal Selection, 2.0 for Slow Selection, and 1.25 for Fast Selection or the IMC PID tuning rules with a filter factor of 1.5 for Normal Selection, 2.0 for Slow Selection, and 1.25 for Fast Selection.
If you want to change some of the tuning factors, click Options | Expert and then change the desired factors. For a more detailed discussion of this feature, refer to the Expert Feature topic.
Once tuning is complete, you can change the setup and calculate new values, try tuning the loop again, or modify the calculated values. You can use the DeltaV Tune Trend display area to monitor the loop response with the new tuning.
Manually Entering Model Parameters
If for some reason you cannot test the process or the process test results do not satisfy your expectations, you can enter or correct the Tune process model manually for both PID loops and FLC loops.
Parameters marked by an asterisk (*) must be non-zero for the selected process type of tuning method. The dialog displays five parameters for non-integrating processes and four parameters for integrating processes. Two or three parameters are marked for particular selections. After clicking the OK button, the entered process model is used for the PID parameter calculations.
The procedure for manually entering model parameters for FLC loops is identical to PID loops. Be aware that you may not get the expected FLC superior performance if the process dead time to time constant ratio exceeds 0.25. In this case, DeltaV Predict is likely to provide better results.
Using Other Features
DeltaV Tune can be used on various processes that operate over a wide dynamic range. This section describes how the default settings associated with trend scaling, testing amplitude, and duration can be changed to compensate for the process range or operating conditions. Following the information in this section ensures that the best possible tuning is achieved for all operating conditions. The Expert selections available in tuning and the options available for saving or printing block tuning are discussed as well. Also included is detailed information about the offline simulation capability that is provided with this product to support DeltaV Tune training.
Modifying the DeltaV Tune Trend Display Area
In the top of the DeltaV Tune window, a trend of the block PV, output, SP, and actual mode is shown. You can adjust the time frame displayed for the parameters shown in the Trend display area using the following selections shown in the toolbar:
The span of the PV, SP, and Output are initially displayed in full range. You can modify the trend range to show values over a smaller or larger range than the default value. In the Controller panel, right-click the box associated with the parameter (SP, OUT, or PV) whose trend range is to be modified.
Scroll Back - Shifts the trend information back in time
by one screen.
Small Back - Shifts the trend information back one unit
in time.
Small Forward - Shifts the trend information forward
one unit in time.
Scroll Forward - Shifts the trend information forward
in time by one screen.
Decrease time span - Decreases the time represented
by the Trend display area by approximately 25 percent.
Increase time span - Increases the time represented by
Then, click Set Y Scale and select either Manual or Auto Scale.
Select either the Compress range or Expand range button provided in the toolbar:
Expert Feature
The Expert feature allows you to retain all Normal selections and select your specific tuning rule to use with the loop response in calculating the best tuning of a PID block. When you click Options | Expert, the available tuning methods for the PID are displayed in the Control Panel area, as shown in the following figures. The figure on the left shows the tuning method selections for non-integrating process and the figure on the right shows the selections for integrating processes. Enable this option by selecting the Integrating process checkbox in the Test Process area.
Compress range - Reduces the span of the selected
trend range by approximately 10 percent.
Expand range - Increases the span of the selected trend
Note: If you are using the Expert feature you should have expert knowledge of the process you are tuning. You must use the Expert feature
with care and always check that the time constant DeltaV Tune calculates represents the actual process time constant. Because the Normal tuning rules give good results in most cases, we recommend the use of the Normal selection for most applications.
Some of the tuning rules provided in advanced tuning are very specialized. For PID and PI loops, use Lambda or IMC tuning rules first. These settings should be satisfactory in most cases. If you have a thorough understanding of loop tuning, you can use some of the alternate tuning rules. If the tuning results are not satisfactory, you can change the rule selection.
For non-integrating processes, the Expert selection provides the following tuning rules:
Ziegler-Nichols - PI - This tuning rule provides the basic rules for calculating controller settings from ultimate gain and ultimate period.
Lambda - PI - This tuning rule allows the desired ratio of closed loop time constant to open loop time constant to be specified through the Lambda factor.
Lambda - Smith predictor - This tuning rule should be used with the PID_DEADTIME Module Template.
Internal Model Control - PID - This tuning rule provides proportional, integral, and derivative control and assumes a first order process with a time delay. During tuning, the model is identified and the tuning values are calculated. The procedure for identifying the model is a patented Fisher-Rosemount Systems technique.
For integrating processes, the Expert selection provides:
Lambda - Averaging Level - PI - This tuning rule is similar to the Lambda tuning rule, but it works for integrating level loops. The IMC tuning rule is especially useful when a process deadtime is longer than half of the process time constant. The process deadtime and the process time constant are shown in the Process Test panel.
when using the Normal selection.
When a process deadtime is equal to or greater than the process time constant, it is beneficial to apply Smith Predictor. For more information regarding application and tuning details, refer to the PID_DEADTIME Module Template topic.
To change the Expert setting, you do not have to retune the loop. Once DeltaV Tune has obtained the process dynamics for a loop, DeltaV Tune can calculate new controller settings for different Expert selections.
Saving and Printing Block Tuning
When tuning a block, you can save the current test data to a file by clicking File | Save File. The parameter values used in the tuning process are saved in the DeltaV Tune folder under DVData. By clicking File | Save File As, you can specify the folder. When you have finished tuning and are closing DeltaV Tune, you are also given an opportunity to save. When initiating DeltaV Tune, it is possible to start the tuning process using previously saved values.
After tuning a block, you can obtain a hard copy of the tuning parameters and selections made in DeltaV Tune. You can initiate this request either by selecting the Print option under File or selecting the print icon in the toolbar. In response, a single page summary of the parameters used in tuning is printed on the user-specified printer.
The Simulator Configuration
As part of DeltaV Tune, two modules containing simulated PID and FLC blocks are provided with your DeltaV system. These modules can be used as a training tool that allows you to become familiar with the tuning procedure before applying it to the actual process.
The simulator modules contain function blocks that simulate a heater process. In order for these modules to be referenced by DeltaV Tune, you only need to download the simulator modules to a DeltaV controller.
The following module templates found in the DeltaV library for the process simulator are provided in the Simulate folder:
DeltaV Tune Simulator Modules
Description Tag Comments
PID Loop and Process Simulation
SIM_SR_PID PID test loop with process simulation
Note You only need to download the simulator modules to one DeltaV controller.
You can view the simulation modules with an interface created by special simulation Dynamos. When you select the detail display from the faceplates for these Dynamos, a representation of the simulated process is shown. These simulator modules do not use real I/O; therefore, they will not interrupt any other module's operation currently running in the controller.
Simulated Response and Robustness Features
Inside this topic
By clicking the SIMULATE button, you can get simulated loop responses for FLC and PID control blocks and robustness plotting and tuning for the PID control block. Simulated responses use the identified process parameters, not the simulation modules described in the previous topic.
Fuzzy Logic Loop and Simulation
SIM_SR_FLC Fuzzy test loop with process simulation
Upon clicking SIMULATE, you will get the following responses:
If the control block is an FLC, the simulated response window will open with a simulated setpoint response.
If the control block is a PID, the recommended tuning parameters will be checked for stability and the PID structure checked for validity and normalcy.
displayed indicating an invalid configuration. You will not be able to proceed to the Simulated Response and Robustness window.
If the robustness calculations determine that the recommended tuning parameters yield an unstable result, a message will be displayed indicating unstable tuning. You can proceed to the Simulated Response and Robustness window by clicking OK in the message box.
If you do not select the integrating process check box and the structure is a P+D, then a message will be displayed indicating that this is an unusual configuration. You may proceed to the Simulated Response and Robustness window by clicking OK in the message box.
If there are no unusual or invalid conditions, then the Simulated Response and Robustness window will be opened without any warning messages.
Simulated Response and Robustness Layout
In the bottom half of the window, there is a simulated response trend plot with performance variables and simulation selection buttons on the right.
In the upper right quandrant of the window, there are entry and recommended tuning parameter display boxes with a RECOMMEND button immediately below them. If the control block is a PID, DT Margin and (if you selected the integrating process check box) % Surge are displayed just below the RECOMMEND button. If the control block is an FLC, DT Margin and % Surge are not displayed.
Simulated Response
You activate the first simulated response when you open the window using the SIMULATE button. Any new tuning parameter entries (or, for the PID, any new robustness map tuning selection) will cause a new simulated response to appear immediately. You may select whether you want a setpoint or disturbance step response simulated for the entry and/or current recommended tuning parameters. Make your selections as follows:
To select setpoint (SP) or disturbance simulated response, click either the SP or DISTURBANCE button.
To cause the current recommended tuning parameter response to be presented with the entry tuning parameter response, select the CURRENT check box.
Any change in your selections will cause the simulated response plot to be updated.
There are three (3) performance variables that are updated after every new simulated response.
Overshoot – Presented as percent of step change by which the process variable overshoots the new setpoint.
IAE – Integrated Absolute Error is presented for all SP responses. IAE will also be displayed for disturbance responses if you did not select the integrating process check box before you clicked the SIMULATE button.
