Category Archive: Measurements

Jul
07

Top Ten Limitations – Turndown

Plant turndown determines how effectively a production unit can minimize inventory and energy costs. As utility rates change with supply and demand, energy efficiency changes with weather, and product demand changes with customer shipments and downstream requirements, the need to be able to run at lower and lower rates becomes increasingly important. Temporarily shutting down a …

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Jul
04

Commissioning Control Systems

The long-term performance of a plant is directly impacted by the care with which the control system is commissioned. Establishing control loop tuning is an important part of the work needed to commission a new plant or an area of the plant in which measurement or control changes have been made. Such work can be …

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Jun
02

Top Ten Limitations – Deadtime

Deadtime sets the ultimate limit to loop performance. Deadtime is any delay in the action needed to exceed the threshold for the start of error correction. The loop deadtime is the sum of pure actuation, correction, or recognition delays and the equivalent deadtime from lags smaller than the largest time constant in the loop. For …

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May
26

Improving pH and Conductivity Performance and Maintenance by Wireless

Wireless technology offers the opportunity to select the best electrode for an application. Spare wireless transmitters can be used to test electrodes in lab solutions set to mimic the concentrations and temperatures of the process. The process lab offers a controlled environment to vary the process conditions of interest and keep other conditions constant. The …

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May
19

Monitoring Process Performance Online

Process efficiency measurements involve the measurement of process flows and utility or raw material flows. The energy efficiency depends upon the utility temperatures and heat transfer coefficient. The raw material efficiency depends upon feed concentrations and the desirable reaction rate to product and the undesirable reaction rate to a byproduct. For simply changing a stream’s …

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May
05

Effect of Noise, Update Rate, Trigger Level, and Stick-Slip on Performance

Since the ultimate limit to loop performance depends upon deadtime, the effect of deadband, noise, update rate, trigger level (threshold sensitivity), and valve sensitivity-resolution (stick-slip) on the best possible performance can be estimated by the amount of equivalent deadtime these terms add to the loop. The dependence of loop performance on deadtime for unmeasured step …

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Apr
19

Tracking Down Disturbances

The first flow that has significantly changed or started to oscillate is normally directly or indirectly associated with the root cause of a disturbance. If the original disturbance is temperature or concentration, the correction in the manipulated flow of a pressure, temperature, or concentration loop is the key to focusing on the right unit operation …

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Apr
07

Top Ten Limitations – Noise

Loops with the highest potential for performance suffer the most from noise. Measurements and final control elements (valves and variable speed drives) with the best ability to respond to small changes are most at risk. If the noise is more than the measurement resolution-sensitivity-backlash, the loop will see the noise as a disturbance. If the …

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Mar
17

Master of Space and Time

The lack of space and time kills process control innovations. The lack of space for new cables, I/O card, and new sensors and the time required for the implementation does more than just slow down implementation, space and time prevents the genesis of new ideas. As I was giving a talk to the American Institute …

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Feb
11

The Latest in pH Measurement and Control

If you want to learn about wireless pH and how to solve pH measurement and control problems, join me for the ISA Web Seminar pH Control Solutions. Last day to register is Feb 15. This is your chance to learn the latest and help ISA, our technical society, to continue to offer educational services. I …

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