Special Tools for Special PID Applications
Some control loops require a broader set of tools to do the job right. PID Loop Optimizer has the tools you need to tune these loops quickly, accurately, and confidently:
PID Loop Optimizer goes far beyond simple PID Tuning. It helps you to address all aspects of PID loop performance. Make sure that you have the tools to do your job properly.
Tune Cascade Loops Using RRT
Cascade loops can be difficult to tune by hand. In fact, most cascade systems are poorly tuned, leading to continuous cycling of the process. ExperTune's PID Loop Optimizer contains all the tools you need to ensure proper tuning of cascade loops.
How to Use Relative Response Time to Tune Cascades
Only in ExperTune, The Relative Response Time (RRT) is a cutting edge tool for decoupling interacting loops. The Relative Response Time (RRT) makes it easy to set interacting and cascade loops to work together. For good control, the RRT in each interacting or cascade should be a factor of 3 away from the others. Change RRT by adjusting the safety factor or lambda time.
How does it work? The Relative Response Time is the period at the peak amplitude ratio in the closed loop frequency response (to load upsets). The PID Loop Optimizer software automatically analyzes the frequency-domain model, and provides the results in a simple, easy-to-interpret number, the RRT.
Eliminate Interactions with Tools for Interacting Loops
Cascade is just one example of interacting loops. PID Loop Optimizer includes tools such as cross-correlation analysis, so you can see how one loop effects another. To prevent interaction, adjust the safety factor or lambda value (set point speed) in the interacting loops so that the Relative Response Time is different by a factor of 3.
Correlation analysis helps you see how one loop affects another.
Find the Root Cause of Cycling
Power Spectral Density helps find hidden oscillation problems and identify cyclic interactions between control loops.
- Helps find the root cause of a plant-wide or unit-wide oscillation
- Shows if an oscillation is hidden in the noise.
- Full story about how ExperTune Power Spectral Density solved a $1 million/day cycling problem. (PDF file, Intech August 1998)
- Lists the 4 largest peak frequencies and their percent energy in the spectrum. The energy tells you how much this peak is contributing to the variability of your product. ExperTune now uses clusters of peaks reducing inaccuracies from leakage and sampling.
- Display frequency and percent energy on peaks in the zoom area only or the entire spectrum
- Optionally use the same chopping and windowing as PlantTriage. This option further decreases inherent errors in the spectrum.
Set Point Filter
By using a setpoint filter, you can get good response to both set point changes and process upsets. Tune the loop for great load rejection and set the filter to eliminate overshoot on set point changes. Select the set point filter option and ExperTune will apply a filter to the setpoint of the simulation of the loop with the New PID settings.
The lag time is automatically set by ExperTune to be approximately the integral time (in seconds). Adjust the lead/lag ratio and instantly see the simulated response. To implement the filter in your system, use your systems lead/lag block or the equations given to program the filter.
Tools for pH Control
Universal Linearizer for pH Loops
Linearization for any pH loop resulting in pH control with little or no cycling. Better pH control improves product quality, reduces reagent costs and helps to keep pH within regulation limits.
pH loops are inherently non-linear and cycle around the setpoint while taking too long to recover from large load swings. ExperTune calculates the characterizer that should be applied to both the measurement and set point of the pH loop. The linearized pH measurement can then be accurately controlled by a traditional PID or other controllers.
The ExperTune pH linearizer Wizard takes you though the following steps:
- From titration data, ExperTune plots the pH curve and converts it to a characterizer.
- Modify the curve (characterizer design) by adding or dragging and dropping points.
- The pH linearizer works with any controller that allows characterization or user programming.
- For easy application of the characterizer within your controller, X-Y coordinates, BASIC, FORTRAN, or C code, are all automatically generated.
Other non-linearities may be caused by the control valve characteristic. Learn how to resolve valve non-linearities.
Tools for Level Control
Tune Level Control Loops Quickly
Get fast payback by:
- Reducing the time spent tuning the loop
- Finding the best tuning, on the first try.
- Maximizing profits by forcing the controls to adhere to the operational objectives.
- Or, Maximizing surge capacity. Ensuring smoother response to upsets, keeping critical quality variables on target.
Level Wizard Helps You Choose the Best Tuning
The level wizard helps process engineers optimize the control strategy of level control loops in all types of process vessels. Level loops present a unique challenge to process control since the control objective varies widely, from tight level control in reactors to averaging level control in surge tanks.
No Steady-State Required
When tuning level loops, it is often difficult to establish a steady-state condition. Integrating processes tend to drift up or down. This is not a problem for users of ExperTune's PID Loop Optimizer software. The software can work with level control data, without requiring a steady-state condition.
Tuning for Surge Tanks
The level control wizard makes it easy to optimize your level loops. It works for all types of level loops. Different level loops have different requirements. Sometimes your plant needs fast and accurate control of level, other times it is best for the level to "float" so the vessel can absorb flow upsets. The wizard guides you through the process.
Read Article on Averaging Level Control , by F. Greg Shinskey
How the Wizard Works
Based on the experience of Greg Shinskey, the level wizard:
- Identifies the goals for the level loop
- Chooses the level control strategy that matches the plant's goals
- Finds the best P, PI or PID parameters to meet those goals
- Provides built-in user guidance (see figure).
PID Loop Optimizer now optimizes level loops with the following level control goals:
- Fast and accurate control of level to setpoint, with and without derivative. The result is the fastest recovery back to setpoint in the face of upsets.
- Averaging level, where the purpose of the tank is a surge vessel to smooth flow
upsets. In this case you are using the vessel to reduce the effects of upstream disturbances.
The goal is that one unit feeding a second should disturb the second as little as possible.
- Averaging level with P action only - level is floating, maximizing the use of the surge vessel to smooth flow upsets.
- Averaging level with P and I action - level floats and slowly returns to setpoint.
Averaging level techniques may use tank volume. Using simple test data, the ExperTune Level Control Wizard automatically determines tank volume and controller settings.
Whatever the performance requirement, whether it be a complex application like a hot vapor by-pass, or a simple surge tank, the new ExperTune Level Wizard guides engineers through choosing and implementing the best level loop control strategy for each individual need.
Read Control Magazine's review of the ExperTune Level Wizard.
Tools for Boiler Drum Level
Inverse Response (Shrink-Swell) Process Analysis, Modeling, and Tuning
Drum level control and bottoms control in distillation columns are examples of the rare loops that exhibit an "inverse response". The PV initially goes in the "wrong direction". These are typically very challenging loops to model and tune. Now simply click to indicate you want an inverse response loop, collect some data, and ExperTune gives you a complete analysis including tuning, modeling of the process, simulation, robustness, valve wear analysis, etc.
ExperTune automatically identifies the process model including process lead, lag, integrator, dead time, and gain.
PID Loop Optimizer Does Much, Much More
Far beyond basic loop tuning, the PID Loop Optimizer Software does much more, including:
- Fast & Easy PID Tuning
- Process Modeling & Advanced Tuning
- Valve & Instrument Diagnostics
- Reporting & Documentation Tools
- Eliminate Interactions Between Loops
- Advanced Control Tools
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