Control Loops Adjust to Process Change – Automatically
Onboard intelligence changes the rules
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Bellevue, WA, June 14, 2007 -- You know how it goes with most applications. Around 20% of the application takes 80% of your attention. Tuning control loops is like that – only more so. Maybe 5% of all control loops cause 95% of the grief. But there is good news: help is on the way. Microstar Laboratories, Inc., maker of Data Acquisition Processor (DAP) boards, has shown how you now can use off-the-shelf components to build a control system that tunes itself. If your system performance suffers because you can't keep important control loops in tune, read on.
Every DAP board includes a processor running a real-time operating system, DAPL, that you control from PC software. You specify the real-time behavior of the DAP board by downloading commands for DAPL to execute at runtime. A new PIZST processing command takes basic PID functionality, and extends it with self-scheduling injection test and analysis processing that does not interfere with control loop operation. The derivative term is not tuned, but can be set manually if you wish.
Iterative Feedback
The gain adjustments use the Iterative Feedback Technique. This approach estimates a gradient direction for loop tuning improvements using measurements – rather than pure mathematical analysis. It does not determine specific gains to apply but produces incremental adjustments that improve existing gains.
The original Iterative Feedback method requires large disturbances inconsistent with online operation. So the PIZST command uses a variation of the original method: a small injected test signal riding on top of a fixed setpoint level signal. Each tuning test cycle is followed by a period of undisturbed operation using the adjusted controller gains. This variation of the original method allows the controller to continue operating online throughout the tuning process. And that opens the door to automatic tuning.
Standard Products
You can use off-the-shelf components to build a control system that tunes itself. Every DAP board runs DAPL, and any DAP board can execute the PIZST command. An application based on a single board using a basic PID algorithm and optimized for multiple channel operation can be updated at time intervals as short as 0.05 milliseconds on every channel, without ever missing an update. And DAP boards work well as multiples in a synchronized network. Of course you may not need this processing power in your application, but it is there for when you do need it. You can download DAPstudio, a Windows application you can use to control DAPL on any DAP board, and you can download the PIZST command to try it out in a proof-of-concept experiment for your own application.
Conclusion
You now can be free from the ongoing operating costs of control loops that require continual hands-on tuning. You can start right away to prove to your own satisfaction that you can build a self-tuning control system for your application from off-the-shelf components. You can read the supporting documentation online and download all the software you need. And you can order hardware for evaluation at no charge. Contact Microstar Laboratories for details.
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Editorial Overview:
You know how it goes with control applications: some key control loops require continual tuning. You don't always have time for this, so system performance suffers. But help is on the way. Microstar Laboratories, Inc., maker of Data Acquisition Processor (DAP) boards, now has shown how you can use off-the-shelf components to build a control system that tunes itself. Every DAP board runs a real-time operating system, DAPL, that you control from PC software. A new DAPL command – PIZST, a self-tuning control algorithm based on a variation of the iterative feedback method – keeps your system in full control during the self-tuning cycles, never interfering with feedback processing. You can read all the supporting documentation online, you can download all required software, and you can order evaluation hardware at no charge. So you can see for yourself almost right away how you could build into your application a control loop that tunes itself.
Note to the Editor:
Microstar Laboratories suggests this text as captions for the available images:
Before and After Self-Tuning – The red trace shows the plant response to a step disturbance. Before self-tuning, the plant is slow to respond and slow to settle. It takes about 40 controller updates to settle. After self-tuning, the plant responds quickly... and settles in roughly 15 controller updates.
An application based on a single board – like the DAP 5216a/627 – using a basic PID algorithm and optimized for multiple channel operation can be updated at time intervals as short as 0.05 milliseconds on every channel, without ever missing an update.
Microstar Laboratories, Inc. claims Microstar Laboratories, Data Acquisition Processor, DAP, and DAPstudio as trademarks. Microsoft has registered Windows as a trademark. Other organizations may claim – or may have registered – as trademarks any trade names, logos, and service marks that appear in this document but not in the list above.
Microstar Laboratories makes it a practice to use an appropriate symbol at the first occurrence of a trademark or registered trademark name in a document, or to include trademark statements like this with the document.