Batch And Continuous Processes Pdf | Control Loop Foundation

Before differentiating between process types, one must understand the basic control loop. Regardless of the industry (pharmaceuticals, oil & gas, food production), every control loop consists of four core components:

The second major section addresses Batch control, governed largely by the ISA-88 (IEC 61512) Standard. This is where the literature distinguishes itself from general control theory. control loop foundation batch and continuous processes pdf

  • Sequential Function Charts (SFCs): Most PDFs and texts visualize batch logic using SFCs, which differ from standard ladder logic by being step-and-transition based.
  • Recipe Management: How to separate the "formula" (ingredients/temperatures) from the "equipment logic" (how the valves open). This allows one piece of equipment to make 50 different products.

    • 1. Feedback Control (The Backbone) The standard loop: Sensor measures output → Controller adjusts input (valve). This is reactive but reliable. Sequential Function Charts (SFCs): Most PDFs and texts

    2. Feedforward Control (Proactive) A disturbance is measured before it affects the PV. For example, measuring a change in inlet flow to a heat exchanger and pre-adjusting the steam valve. Combining feedback + feedforward is the gold standard for continuous processes. Continuous processes operate 24/7

    3. Cascade Control Used for slow processes (e.g., reactor temperature). An inner "slave" loop (flow) responds faster than an outer "master" loop (temperature). This isolates disturbances before they propagate.

    Tuning Note for Continuous: Use Ziegler-Nichols or Cohen-Coon for initial tuning. Focus on quarter-wave damping. Integral action is critical to eliminate offset, but too much causes "windup."

    Continuous processes operate 24/7, with raw materials entering and products exiting without interruption. Examples include: oil refining, ethylene production, water treatment, and power generation.