John Egnew, Fisher-Rosemount Educational Services
Articles
Positioner Guidelines
G uidelines are never a substitute for good engineering practices and experience but they are better than proceeding down a trial-and-error learning path. Guidelines for all positioner types Positioners can reduce control valve deadband caused by friction. Most control valves without positioners, even those using 'low friction' packing material, may demonstrate a 5% deadband. Deadband greater than 1% can produce loop controllability problems.
Open-Loop Response Testing Improves Process
Three-quarters of all process control loops are operating below peak efficiency, according to one industry survey. Among conditions that can reduce process efficiency are improper control valve selection, sizing, or calibration; instability or oscillation above and below a setpoint; slow response to changing conditions; or a combination of these factors.