What is Feed Forward Control?

To no practitioner’s surprise, process control exists as a discipline because manufacturing is complex. It’s erratic and occasionally unpredictable. At many facilities it is highly hazardous. Variability – whether localized to a single process or reverberated throughout a plant – can transform production from a well-managed operation to a highly turbulent task. Variability is a key reason why manufacturing is difficult. So it’s no wonder that process engineers focus their efforts on controlling disturbances – those unplanned upsets which drive variability from one process to the next.

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When Cascade Control Isn’t the Right Solution

Sometimes looking for the right answer can be difficult especially within the realm of process control. While it can be easy to identify solutions that satisfy some requirements it can often be a challenge to find options that meet multiple success criteria. Something usually has to give. Indeed, sometimes it’s easier to consider the reasons not to do something. Applying a philosophy of ‘no’ can be particularly helpful when considering Cascade Control.

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The Pros and Cons of Cascade Control

As shared previously Cascade Control is an advanced application of Single Loop Control. Through the use of a secondary and faster PID control loop, practitioners can improve a given process’ ability to correct for known disturbances. Although it is considered an advanced strategy, Cascade Control is commonly used across the process industries.

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Overview of Cascade Control

While Cascade Control is generally considered an advanced control strategy, it is only marginally more complex to implement than Single Loop Control. More often than not it is applied to improve the performance of a slow process such as temperature that demonstrates sluggish behavior. Essentially Cascade Control improves a “slow” control loop’s ability to respond to disturbances by capitalizing on the dynamics of a faster one – something quicker like a flow or a pressure loop. The faster loop provides an early warning variable that facilitates disturbance rejection, helping to maintain steady performance of the slower primary loop.

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What Is Cascade Control? How Is Cascade Control Configured?

As they say: Timing is everything.  The lag between upset and response directly impacts a system’s performance along with the performance of other processes with which it interacts.  Fortunately, there are a variety of approaches available that leverage the PID’s capabilities.  These approaches improve a system’s ability to reject the negative impact of disturbances.  Cascade Control is among them.

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