NOV-DEC 2017

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INTECH NOVEMBER/DECEMBER 2017 51 AUTOMATION BASICS trol functions like P&ID loops to operate. Operators can train on the system, because the simulator only reacts to the outputs that, in tur n, only react to the main pro- gram or the operator, just as would actually happen. Simulating up- sets by interr upting the feedback; by simulating high temperatures, pressures or flows; or by inhibiting interlocks and per missives, pro- vides an effective, low-cost, and low-overhead training and soft- ware validation tool. n ABOUT THE AUTHOR Michael Whitt ( is an ISA Senior Member and the man - ager of integrated control systems at Mesa Associates, Inc. His book is Suc - cessful Instrumentation and Control Systems Design. SIMULATE PUMP10 STOP: If not(PUMP10_OUTPUT) then Wait 0.5 Clear PUMP10_AUX Endif; If not(PUMP10_AUX) then Set DISCH_FLOW = 10% Set DISCH_PRESS = 10% Wait 1 Set DISCH_FLOW = 0% Set DISCH_PRESS = 0% Endif; prevent the action from taking place. At this point, the pump is run- ning, and process conditions are set to reflect that. Fluids are flowing, and pressure has risen to 50 percent of scale. Changing flow and pres- sure will cause the system to react. For example, a high-pressure inter- lock might shut down the pump. The user can now enter a high-pressure value and demonstrate that the soft- ware does in fact remove the PUMP_ OUTPUT command. (see left) At this point, the pump has stopped, and process conditions reflect this with flow and pressure at zero. Low-cost approximation The purpose of a simulator is to approximate the behavior of ex- ter nal equipment, not to bypass or simulate inter nal logic. Passive loopback process simulation will provide a low-cost, first-order ap- proximation of how the plant will react to the software. It will allow sequences to function, alar ms to activate, and even high-level con- FIRST CLASS REMOTE ACCESS SECURE - SIMPLE - SCALABLE Want to save travel costs? Need to optimize your production? Reduce machine downtime? visit us: One platform for remote access, monitoring and M2M Convert Your Mobile Device into a HART Communicator … with our Advanced HART-based Products C O N N E C T > C O N F I G U R E > D O C U M E N T Complete DD-based HART Communicator for any device - PC, Tablet, Phone. Your choice! Complete DD-based HART Communicator for any operating system - Windows, iOS, Android. Your choice! Full line of registered HART Modems - USB, RS232, Bluetooth, Bluetooth Low Energy Your choice! Use your own host device or one of our complete systems. Hazardous area options available. Significant cost savings • Mobile convenience • Satisfaction guaranteed NEW! iOS Version now available!

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