Radar offers an incredibly sensitive measurement of surface level that can be nearly maintenance free. The potential for an accurate inventory measurement is dramatic but with this extreme capability comes some extraordinary application considerations. A checklist is offered of implementation details to help achieve the full capability of this measurement.

Variable speed pumps can save energy when the flow is reduced. However, the turndown of the pump speed may not achievable if there is overheating at low flows, excessive sensitivity at low rpm, and cycling at high destination pressures. Special attention to variable frequency drive (VFD), motor, pump, and piping system design is necessary to achieve the rangeability associated with the energy savings.

The threshold sensitivity and resolution of measurements (smallest incremental change) has improved dramatically to better than 0.05% with new sensor technology and smart compensation of extraneous effects of operating conditions. The response of the air-actuated control valve has improved, but the smallest incremental change in position varies widely depending upon the actuator, positioner, valve type and valve heritage.

The value of a key PID feature is increasingly becoming apparent. I got a preview of the importance when I found the 1980s vintage DCS required a fix for override control that was inherently addressed in the next generation of DCS by this feature. This wakeup call was followed by the realization this feature offered improved analyzer, blend, cascade, decoupling, feedforward, surge, valve position, and wireless control with a side benefit of simplified deadtime compensation.

The questions submitted by the 10 worldwide participants in ISA Mentor program are refreshing and cause one to stand back and think about how we do things and how can we convey knowledge we take for granted. We have posted the answers to the 18 questions to date to help the emerging new generation of automation engineers and give the mentored some recognition for their participation in this endeavor. For leaders in the automation industry whether users or suppliers, the Q&A enables us to better understand how we can provide the information and tools needed.

We conclude this series with a look at control schemes that can increase process efficiency for distillation control, compressor control, and neutralizer control. These control schemes can inherently reduce process variability and controller tuning difficulty and for compressors increase onstream time. Process control improvements can be ready for operator training by the use of a virtual plant to test the configuration for a full spectrum of process conditions including abnormal situations in a matter of days.

In April's Control: Remote Access Goes Mainstream. Find out why it's one of the fastest-growing and accepted technologies to hit the process control industries; plus, how an upstate New York brewer saves $230,000 a year with a flow controls upgrade; what's new in SCADA; and the story of Southern States Chemical's new sulphuric acid plant, built with a combination of recycled equipment and the latest in processing technology. Also, don't miss this month's Control Talk, featuring Greg McMillan and Stan Weiner's column "New Paradigms for Lab Control Systems."

What configuration changes to control strategies can readily take advantage of improvements in measurements and final control elements? Control strategies can inherently improve production rate by maximizing feed and efficiency by enforcing material and energy balances. In part 3 and next week in part 4 we look at control strategies for unit operations that have a major effect on product quality, production rate, and energy use. The configuration modifications can often be made and tested within a few days if a virtual plant is used to prototype and test the control strategies for the entire range of possible process conditions including abnormal operation.

Process efficiency can be increased by eliminating the excess use of reactants, reagents, and energy, eliminating the production of waste and off-spec material, and taking advantage of low energy and raw material sources. Not well recognized is effect of sensor drift and location, missing measurements, abnormal operation, process understanding, control strategy, deadband, resolution, and threshold sensitivity on optimum operation.

When we saw an increase in production rate needed during opportunity assessments at Monsanto and Solutia, we would salivate. Impressive results could be obtained in a matter of a few days by a simple change in setpoint, tuning, and/or configuration. These were quick hits and were often done right at the end of the opportunity assessment while motivation and enthusiasm was at its peak. Once we left the plant, other priorities often sneaked into the picture. Everyone then like now had more than enough to do as a result of meetings, procedures, and paper work.