Effective control system simulation
Aug. 14, 2012
by Erick Braaksma, control systems engineer, POWER Engineers
An appropriate level of simulation of programmable logic controller (PLC) and human-machine interface (HMI) programming is an effective tool to validate software before it is delivered to the end user. In many cases with today’s technology, accurate process models can be developed with minimal effort by the programmer. This process begins with accurate piping and instrumentation drawings and a thoroughly reviewed and approved control philosophy.
In today’s factories, there are many layers to a network. When the network connectivity is not configured properly, many undesirable conditions can arise. Network simulation can be accomplished using virtual machines so that each of the control system components can be configured and tested prior to implementation at the facility. For example, the domain controller, HMI, tag server, PLC and historian can be configured on separate virtual machines, and all configurations can be set up and tested. In some cases proprietary networks can be set up using real-world hardware to effectively simulate the hardware that will be installed in the project.
One must take into account the level to which a process is simulated or modeled. In the discrete world of valves, switches, push buttons, and motors, it is relatively easy to write code that will simulate the “on” or “off” status of equipment. This can be done in the control system processor in a separate module that does not change the runtime software. This simulation goes a long way in testing system functionality, required interlocking, and correcting logical and graphical errors. This type of simulation, in many ways, is equivalent to a factory acceptance test (FAT) that can be reviewed and approved by the customer.
Analog process simulation can be a much more complicated and time consuming task. A detailed evaluation of the process physical parameters is required by the process engineer. In some cases, analog simulation is part of the process control modules offered by the process control vendor software. In other cases, it can be purchased in a third-party software package. In either case, the functionality of the control software can be tested for proper functionality.
Benefits of system simulation
An investment in this pre-startup simulation and testing is justifiable because it can:
- Lead to on-time startup
- Save valuable time in the field by reducing troubleshooting cycles
- Reduce startup and commissioning expense while getting product out the door sooner
- Reduce rework of code in the field
- Improve customer input in the functionality of the control system.
When complete, the simulated system can be used as a valuable training tool to teach operators how the new system will look and function. This can even be done before the equipment is in place. Operators will then be prepared for the actual startup minimizing their own startup curve.
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