What is the Purpose of a PID Controller’s Integral Term? Why is PI Control So Widely Used in Industry?

In the realm of process control it makes complete sense that the primary goal is – you guessed it – to control the process.  For decades the PID controller has proven a reliable tool for fulfilling that objective.  Even so, there are various forms of the controller that can be used and each has its unique performance attributes.  In spite of the added complexity associated with the Integral Term the PI controller is the form most widely used in industry.

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Where Can I Purchase RSTune?

Nowhere…Because RSTune and RSLoop Optimizer Were Discontinued in 2011!

Product names often outlive the products themselves. Investments made to establish a product and a brand can have a lasting impact.

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Who Benefits from Process Control Training?

No surprise, as the demographics of industrial automation continue to shift a graying workforce is giving way to a younger, greener one. More and more staff are retiring just as the “automation oracles” predicted. In tandem with that trend investments in training and skills development are recovering from previously reduced, recessionary levels. With those budgets being restored some somewhat surprising questions keep popping up: How should process manufacturers apply their newly reinstated funds? Who should attend?

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What is On-Off Control?

On-Off Control is not a highly sophisticated control method. Even so, examples of its practical, everyday use can be found all around. Look no further than the appliances in your home. Kitchen appliances such as ovens and refrigerators utilize On-Off Control. Similarly the furnaces, water heaters, and air conditioners found in most basements rely on On-Off Control. Although it’s unsophisticated, On-Off Control plays a significant role in our lives.

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What is Feed-Forward Control?

In a previous post cascade control was introduced as an effective means of limiting the lag between an upset and the associated PID control loop’s correction. As practitioners know: The longer the delay in responding, the larger the negative impact on a process. Like cascade, Feed-Forward enables the process to preemptively adjust for and counteract the effects of upstream disturbances.

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What is Proportional-Only Control? When Should P-Only Control be Used?

Place in Industrial Process Control.
As with most everything in process manufacturing, PID controllers require practitioners to make choices. One of those choices is which form of the controller to apply on a given regulatory control application. In a previous post the pros and cons of Derivative and the full PID were covered, and now the advantages and disadvantages of Proportional-Only control are explored. Due to performance characteristics the selection of a P-Only controller can be relatively straightforward and among a practitioner’s easier choices.

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How Do I Tune a Temperature Loop?

Temperature is one of the more common types of self-regulating – also known as non-integrating – processes used in industry. Like other self-regulating loops, temperature loops tend to naturally settle at a new operating state when adjustments are made to the corresponding Controller Output. What’s more, temperature loops are nonlinear in their behavior and process dynamics can vary considerably from one range of operation to the next.

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What Sample Rate is Needed When Tuning PID Controllers?

Practitioners often apply simple guidelines when it comes to data collection requirements and controller tuning. These “rules of thumb” assure that sufficient data resolution exists when a given PID control loop’s dynamics are being analyzed. Without good data a process engineer’s ability to model the dynamics and tune for improved control can be undermined. If the sample rate is too slow, then most any tuning procedure will be hit-or-miss at best. So what exactly are those guidelines?

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Default Out-of-the-Box Settings Prevent the PID Controller from Achieving its Goal

Tuning a PID controller doesn’t have to be hard. Whether a practitioner chooses to tune control loops manually or with the help of software, the procedure is relatively straight forward and can produce highly effective results. It can be argued that using software is faster and provides more optimal results than manual tuning, but that’s an argument that largely depends on the economic importance of the PID control loop in question. In the end, the goal is the same: To tune for improved control loop performance.

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How Does the Derivative Term Affect PID Controller Performance?

Derivative is the third term within the PID. In mathematical terms the word derivative is defined as the slope of a curve. Seen in the context of strip chart data derivative represents the rate of change in error – the difference between the Process Variable (PV) and Set Point (SP). Like the proportional and integral terms within a PID controller, the derivative term seeks to correct for error. Valuable as the third term can be in maintaining effective control, experience suggests that appropriate uses of derivative are not entirely clear.

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