Rossi adds, We use simulation for initial training on major changes in software programming, and to wring out the software logic before we deploy it into the process. Our results have been quite positive. If we can train the operations on 90% of the what-if scenarios they may run into, we're golden.
Glen, the paper company engineer, cautions that you have to keep a close eye on the contractors when using a simulator to avoid getting bogus information. Consulting engineers rarely have all the right information at the beginning of a project, such as valve sizing, pipe sizes, flow rates and other critical information that affects the simulation, he says. Whats more, as various contractors are involved in the construction of a plant, not everybody talks to each other. Typically, we give them specs, which include a simulator. The simulator finds design problems, so we expect the real controllers to match the simulation parameters. To make a simulator work well, you have to manage the suppliers closely, so any design or equipment changes are incorporated into the simulator, and any changes called for by the simulator get relayed to the contractors.
Ferrer adds the OTS provider must protect itself. The design suffers changes as the project develops, he says. To prevent this, the OTS supplier establishes dates to freeze the project data. After that, every change has an extra charge, as it requires rework. Sometimes changes such as valve sizing or location are suggested by the operators during training sessions or control studies. This is good because its better to discover mistakes before startup.
As with any project, accurate information is essential to the overall success, adds Siemers. Change management is essential to prevent unnecessary delays and cost overruns. Effective, timely, and accurate communication is the best defense against this type of scenario. Users can prevent this by taking proactive steps to establish clear lines of communication for all project participants, and conduct regular change audits.
McKim adds, An emerging trend is to combine steady-state and dynamic simulation with front-end engineering design (FEED), in which design and analysis tools share connections to a common design database.
Henderson agrees. I wouldn't call it bogus information, but there are several phases through the engineering process where design and equipment information is refined, he says. FEED data is all theoretical performance around the design basis. You wouldn't build an OTS on this data, but you might create more focused simulations to dynamically visualize and validate design assumptions. During the detailed-design phase, EPC vendors will update the FEED design, and update equipment performance with information from selected vendors.
These issues are normally handled in the OTS design phase to align with customer expectations. In older plants, the data may not exist or wasnt updated or maintained during years of plant transformations. The original heat/material balance may no longer apply. In this case, the OTS project may need a new simulator design basis.
Standalone vs. Connected
Simulators fall into two broad categoriesstandalone and connected. A standalone simulator operates completely independent of the process control system. A connected system provides simulated inputs (sometimes called stimulated) to an actual control system.
Ideally the process control system and training system exist on separate networks, says Siemers. This is a key advantage of a training simulator because it removes the potential risk of upsetting the process on which the operator is training.
March adds, We see our customers using simulators in standalone mode most frequently. With the modular approach to simulation, process dynamics and system response can be accurately represented even in an offline manner. This ensures theres no possible disturbance to the live, running process.
In our case, a simulator is a real control system thats the same as the one running the machine tools on the manufacturing floor, says Gary Highley, product manager at GE Fanuc Automation, which makes simulators for discrete automation applications, such as machine tools. Ladder logic to control a machine function and parameters for testing servo systems can all be adjusted. Its a standalone system thats been slightly modified, so it doesnt have to be attached to the machine tool, and all of its various switches, motors, and valves operate. These simulators can run the same programs and ladder logic as on the shop floor. A range of scenarios can be trained for, tested, or developed. It can safely test scenarios you wouldnt dare try in a real manufacturing process.
Siemers adds, Control modifications required for plant operation can be verified for proper operation on the simulator, and then implemented in the plant. Customers who have taken advantage of this type of testing and pre-startup training have had excellent first-time start-ups. Eliminating extra start-up days through manufacturing control system checkout using a fully rigorous dynamic model is a common justification for buying the simulator.
Opto 22 also has a hard simulator. The SNAP Ultimate I/O Learning Center is a fully functional, complete package of hardware and software that provides everything needed to learn and train with Opto 22 Ethernet-based technology, says James Davis, application engineer. You get to configure I/O points, read and write to those points, create flowcharts as part of a control strategy, and build a graphical user interface. And you can test the hardware and the strategies you create using built-in LEDs, potentiometers, temperature probes, voltage meters, and other instrumentation.
Ed Kirk, assistant professor of the regional occupational program at Palomar College in San Marcos, Calif., uses an Opto 22 system to help teach air conditioning, refrigeration, heating, and controls at the entry level. I use simulation to set up and demonstrate how equipment works, he says. This process includes graphic displays of any process I can develop. This system allows for changes in operation with real-time displays of whats happening to the equipment. Ive adapted things like single-phase fan controllers with a temperature input to be directly controlled by an analog output module instead of the temperature sensor. Ive have gotten to a point where its difficult to tell the difference between simulation and real-world applications.