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Dec
16

Star Performers in Minimizing Life Cycle Costs

Projects tend to focus on purchase price of the control and automation system even though it is a small fraction of the total life cycle cost, which in my book includes the cost of implementation, maintenance, and any adverse effects on process variability. Hunter Vegas’s #1 “Piece of Advice” in The Final Word on Instrument Upgrade Projects says as much.

Below is my short list of what I would choose to minimize physical installation costs, installation effects, the need for calibration checks (real or imagined), and process variability from poor precision.

PID Control

I would use the enhanced PID algorithm for wireless (PIDPlus), which does not require retuning to prevent oscillations when you go to wireless instrumentation. The PIDPlus also naturally kills oscillations from analyzer cycles times (Deminar #1), backlash and stick-slip (Emerson Exchange 2010 Short Course), feedforward timing errors (Deminar #11), split range discontinuity (Deminar #12), and valve position control (VPC) interaction (Deminar #13).

Field Measurements

The measurements on my short list have a sensitivity, rangeability, and drift that are an order of magnitude better than other choices. The installation effects are also minimal.

For temperature, I would use wireless smart RTD transmitters integral mounted on thermowells with sensor matching calibrations for maximum temperatures less than 500 degC without damaging vibration. For more details see Temperature Measurement, Control Key to Plant Performance. For flow, I would use the elite class of coriolis mass flow meters for lines sizes up to 6″, as permitted by materials of construction and solids. For level, I would use radar level measurements wherever the dielectric constant was high enough and the tank geometry does not provide obstacles. For pressure, I would use the elite class of smart pressure transmitters, integral mounted if accessible on the pressure tap to eliminate impulse lines. For pH, I would use wireless smart pH transmitters and high temperature electrodes with embedded calibration records. I would use 3 pH measurements and middle signal selection for control.

Control Valves

I would use low friction packing, diaphragm actuators, and digital smart positioners and sliding stem valves for line sizes up to 8″ where solids or polymer accumulation is not an issue.

Project Managers

I would prefer managers who have read this and my entries on “Measurement and Valve Errors – Sources and Impact” , “Secret Installation Effects” , and “Exceptional Opportunities in Process Control – Middle Signal Selection” and have viewed my Deminars.