When considering whether adaptive tune control is right for an application, there are several key aspects to explore. This article explores the importance and features of adaptive tuning, and the factors to consider when considering adaptive tuning for your application.
Adaptive tune, as the name indicates, adapts to the dynamics of the process and will tune "on the fly," responding to certain process criteria as determined by the specifics of the adaptive algorithm being used. It changes the PID values to respond to the change in the process. When applied properly, it is of great value in taming hard to tune process loops. It will also tune a typical process loop more precisely.
Determining Adaptive Tune Needs
Adaptive control algorithms can improve tuning in virtually any process because the user no longer needs to be a tuning expert, nor do they need to call on one.
Even an expert, however, cannot feasibly tune some processes, because they require re-tuning as conditions change. This is true for processes that are operated at a wide range of set points such that the PID parameter values must be different at different set points. It is also true for processes that routinely undergo load changes, such as exothermic chemical reaction or shear heat that results from a plastic extrusion process.
Adaptive tune is ideal where a tuning expert is not available because it applies "built in" expertise. All the operator must do is set up the sensor type and output type (such as time proportioning, or burst fire), set a set point and set the control mode to tune. Then, the algorithm takes charge.
Most applications are not so dynamic that they require adaptive tuning, but virtually any process can be better tuned. The resulting PID settings (proportional band, integral reset and derivative/rate) will better reflect the thermal characteristics of the process.
The Benefits of Better Tuning
When a process is well tuned, processed materials are kept closer to the target setting. This improves yield and reduces scrap and rework of mis-processed material. In addition, when the process variable tracks the set point better, the process spends less time warming up and stabilizing, making it available and productive more of the time, which helps save capital and energy costs.
Most adaptive algorithms will work well across a range of different type of processes. That is, faster or slower responding loops. A faster responding process often calls for a higher proportional value, a lower integral value and in some cases even turning the derivative to zero. Whereas a slow responding loop will typically call for a lower proportional value and higher integral value. The adaptive tune will automatically compensate for these differences in requirements.
TRU-TUNE®+ Adaptive Tune
While there are similarities between the different adaptive tune algorithms, they each have their differences. The following shares some insight as to how Watlow implements their adaptive tune, called TRU-TUNE®+.
"Tune Band" used in this algorithm describes the process when the variable is within this band around the set point. When this occurs, TRU-TUNE+ adaptively tunes the PID parameters. When the process variable is outside this band, no tuning is performed. This prevents undesirable de-tuning of the PID parameters.
"Tune Gain" is the parameter that determines how responsive the algorithm will be to deviations from set point and set point changes. Since the responsiveness is actually a user preference dependent upon the relative importance of preventing overshoot and minimizing time-to-set-point, this parameter is not set automatically and may be changed by the operator. There are six settings ranging from one, the least aggressive response and least potential overshoot (lowest gain), to six, with most aggressive response and most potential for overshoot (highest gain).
Watlow products that use the TRU-TUNE+ adaptive tune include EZ-ZONE™ ST integrated control loop, EZ-ZONE PM integrated controllers and SERIES SD temperature PID controllers.
|
