Archive | Technical

industrial laser with sparks flying around

Tip #101: Use Plant-Wide Feedforward for More Flexible and Efficient Production

The pressure to reduce inventories, coupled with changing market demands and fluctuations in raw material and energy prices, requires a process plant to be able to respond quickly to maintain optimum operation. To most efficiently support changes in production rate or product grade, flows must change in unison throughout the plant. Feedback loops cannot do […]

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Factory control room

Tip #89: Identify Deadtime and Ramp Rate

In Tip #70, we learned that deadtime was the key to loop performance. The Control Talk blog The ABCs of Controller Tuning describes how tuning settings can be reduced to a simple function of deadtime. The InTech article PID Tuning Rules and the article’s online appendices describe the fundamental relationships between deadtime, performance, and tuning. […]

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Chemical factory

Tip #94: Smooth the Transition between Batch and Continuous Operations

Processes often include a mixture of batch and continuous operations. For liquid products made in a batch operation, most of the time the batch flow is off because the drain valve is closed during the batch. When done, the batch is drained quickly. This discontinuous batch flow cannot directly feed continuous operations downstream. For traditional […]

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Brewery contol display

Tip #95: Use External-Reset Feedback for Cascade Control and Slow Final Control Elements

The value of the external-reset feedback feature in PID controllers is becoming increasingly apparent to me. I got a preview of its importance when I found that 1980s vintage DCS required a fix for override control that was addressed in the next generation of DCS by this feature. This wakeup call was followed by the […]

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Colorful pipes

Tip #84: Use Signal Characterization in the DCS to Linearize Valve Installed Flow Characteristic

Signal characterization to linearize valve installed flow characteristic has a bad reputation due to some practical implementation problems. These problems can be addressed today by doing the characterization in the distributed control system (DCS), but the stigma remains. With pneumatic positioners, signal characterization was done by the use of a cam. Standard cams were based […]

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oil valve

Tip #97: Use Valve Position Control to Optimize Process Efficiency and Capacity

There are many opportunities for process optimization by valve position control (VPC). Table 1 summarizes common examples of the use of VPC for increasing process efficiency and capacity. Efficiency is increased by reducing energy and raw material costs for a given production rate. Capacity is increased by increasing feed rates for a given efficiency. Table […]

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Tip #98: Achieve the Required Simulation Fidelity

The best way to classify process simulators is to look at the original intent of the simulator software when it was first released, who the software developers were, who configures the models, and how the models are used. Simulators originally designed for system acceptance testing (SAT), operator training systems (OTS), and process control improvement (PCI) […]

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Young Women Operating The Control Panel

Tip #87: Monitor the pH Offset to Determine the Health of a Reference Electrode

The reference electrode should provide a fixed reference potential and a path of electrical continuity from the internal reference element via a porous surface or aperture between the reference electrolyte and the process called a liquid junction. Coating of the reference junction can cause slow equilibration. Process ions, such as cyanide, can cause precipitation of […]

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