The following information provides common examples to illustrate how some of InSight's performance monitoring key features can be used in an operating plant.
A new plant area is being commissioned. The new area is selected in DeltaV InSight and Process Learning is enabled on all loops in the area. As the new area is brought on-line, the operator places some loops in Manual while other loops are placed in Auto using the default tuning or an estimate of the tuning that was entered during system configuration. During commissioning, the process engineer responsible for the new area notices that DeltaV InSight indicates that tuning recommendations are available for many loops in the new area. Using the Models Viewing page in Tune with InSight, the engineer confirms that the models identified by DeltaV InSight are consistent and control can be improved by the recommended tuning. He applies the recommended tuning and notices a significant reduction in process variability.
A critical process input flow loop is designed to run normally in Cascade mode with its setpoint set by a composition loop (the loop's Normal mode element has been configured as Cascade). However, on the midnight shift, the operator changes this flow loop to Auto because of wide fluctuations in the setpoint. The next morning, the process engineer for the plant sees that InSight flagged the actual mode as being incorrect for more than one percent (1%) of the time. The process engineer can use this information to quickly determine that a problem existed in the primary loop tuning. By quickly identifying and resolving this problem, the process engineer can minimize any off-specification product that resulted from manual adjustment of this key flow.
An instrument technician for a power plant notices InSight showing the oil flow control loop as being limited in operation. The instrument technician finds that the setpoint for the oil header pressure control was below the design pressure, forcing the oil valve to go completely open under heavy load conditions. By adjusting the pressure back to its designed target, the oil valve can now meet its setpoint without going completely open.
InSight flags a key temperature measurement as Bad over one percent (1%) of the time over the last day. The instrument technician examines the transmitter calibration again and finds that the device was calibrated for too low of a temperature range. The instrument technician resolves the problem by recalibrating the transmitter for the correct temperature range. Recalibrating the transmitter might improve the accuracy of the measurement. Any improvement in accuracy of the measurement also improves the process operation.
During normal operation of the plant, a plant engineer sets all Variability Limits to the current value plus ten percent (10%). After a few weeks, he notices that InSight flagged a critical flow loop as having excessive variability for a significant period of time. Upon further investigation, he finds that the valve positioner connection to the valve stem is loose and is causing the control loop to cycle severely. After fixing the valve positioner, Variability Index returns to its normal value.
The normal value for the Variability Index limit for a specific block varies with the associated process dynamics, normal disturbances, and so on. Use InSight to detect when Variability Index increases dramatically from its normal value. Often, such an increase indicates a change in the process, measurement element, or control element that needs attention.