HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Artificial Intelligence, Fuzzy Logic and ControlOne area where this software capability to turn data into informationis valve diagnostics. Control valves make many small movementseach day to control parameters such as pressure, temperature, or flowrate to an optimum level for efficient plant operation.Diagnostic tools can measure valve and valve actuator characteristicsto determine whether or not such control valves are functioningproperly or require maintenance. Analyzing the valve actuator pressureversus valve travel can provide information on friction, actuator springcompression and galling. This information can be important in reducingdowntime and maintaining optimum system performance.Fieldbus communication protocols can provide the two-way communicationsneeded. Using this technology, a smart valve positioner cansend information back to the controller concerning its actual final positionusing the same wires as the outgoing signal.The sensors throughout the plant also provide an opportunity forsignificant operational improvements. Advanced calibration monitoringsoftware uses mathematical techniques to predict an expected valuesuch as temperature or pressure. The software computes the statisticalvariation from the predicted value. This software keeps track of theamount of time each sensor is beyond the setpoint limit and generatesa report that flags those devices that are in need of maintenance.A new generation of valve controllers, called digital valve controllers,provides valve diagnostic capabilities. This is part of the evolutionin distributed controls. Low-power microprocessors allow these digitalvalve controllers to operate on the power from the standard 4-20 mAinstrument wiring. The HART communications protocol superimposes adigital signal on top of the 4-20 mA analog signal. This provides thecontrol loop along with two-way communications with the valve controller.PC and Windows-based software can communicate with the controllerto obtain the valve diagnostic variables. The data can be plottedwith the software to determine the condition of the valve.Neural Network ModelingBesides linking the plant operations with the control of maintenanceactivities, an additional part of enterprise management is systemmodeling and the resulting analysis.©2001 by The Fairmont Press, Inc. All rights reserved.