Control for Hard Cases: Zero-Shaping
PIDZST Command Includes Self-Tuning
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Bellevue, WA, March 21, 2008 -- Does your process control application respond well to derivative and zero-shaping strategies in classic PID control, but your process changes over time so that it is not possible to get the full benefit from these features? Microstar Laboratories – maker of Data Acquisition Processor (DAP) boards for PC-based applications – may have something for you. The company now has available control software for systems that need frequent loop-tuning adjustments to track command-level changes consistently, to avoid poorly damped oscillations, and to maintain a good response time as conditions change. Ordinary derivative gain can become less effective or in some cases aggravate a tendency to oscillate when a control loop is poorly tuned. Applying a "zero shaping" gain on the command input – as done in the PIDZ command for a DAP board – can reduce tracking errors but can slow response if this adjustment becomes unnecessary.
A new self-tuning PID command, PIDZST, includes the extensions of the PIDZ command, but also optimizes controller gain parameters in real time to allow for plant characteristics that may change while the process is running. Every DAP board includes a processor running a real-time operating system, DAPL, that you configure and monitor from PC software. You specify the real-time behavior of the DAP board by downloading commands for DAPL to execute at runtime. The new PIDZST processing command is best suited for applications in which natural disturbances are relatively rare and not sufficient to provide adequate loop tuning information. PIDZST provides a self-scheduling, low-level injection test plus analysis processing that runs in real time and does not interfere with control loop operation.
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 PIDZST 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 PIDZST 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 stubborn control loops that tend to oscillate or overshoot and 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:
Some processes change over time, so that it is hard to apply the PID approach and its extensions without continual tuning: what was a good tuning degrades into one that tends to oscillate, overshoot, or respond slowly. If your application faces these issues, you may want to take a look at new control software available from Microstar Laboratories – maker of Data Acquisition Processor (DAP) boards for PC-based applications. You now can use off-the-shelf components to build a control system for hard-to-control processes. And the system tunes itself. Every DAP board runs a real-time operating system, DAPL, that you control from PC software. A new DAPL command – PIDZST, a self-tuning PID control algorithm with zero-shaping – 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 a caption for the available images:
PID control action and system response after automatic tuning by PIDZST. Notice the disturbance level of about 100 units compared to the operating level of about 16000 units.
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.
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