Archive | Process Measurement & Control

ISA Process Measurement & Control Division

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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man working at programmable machine

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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Pharmaceutical machine operating

Tip #88: Use Middle Signal Selection to Improve pH Measurement Reliability

Biopharmaceutical batches are often worth more than a million dollars. The product quality of these batches is sensitive to changes of 0.1 pH and the steam sterilization of electrodes reduces the life and accuracy of a sensor that under the best of conditions is the weakest link in a control system. Yet people looking at […]

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