Process simulation can be an extremely useful tool when working with a control system. Thus, chapter 15 of Control Loop Foundation – Batch and Continuous Processes addresses how to add process simulations to a control system using tools that exist in most control systems. The material in this chapter on process simulation is broken into three parts:
- Techniques for adding a process simulation to a control system
- Developing a process simulation starting with the Piping and Instrumentation Diagram (P&ID)
- Simulating process non-linearity
In this blog and following postings I will cover some of the key concepts that are addressed in much more detail in the book.
Integration of process simulation to work with the modules of control is made much easier if the control system has adopted the Fieldbus Foundation analog and discrete input blocks. The processing of these input blocks may be altered by simply enabling the Simulate parameter, as illustrated below
When simulation is enabled in an input block, a Simulate parameter value is used in place of the field measurement. Thus, the simulated process output values may be used by analog and discrete input blocks in place of field measurements. Via this basic capability of the control system, process simulation may be incorporated by one of two means:
- Embedding Simulation in existing modules
- Adding Process Simulation modules
In most of the modules used in the 19 workshop exercises included in Control Loop Foundation – Batch and Continuous Processes, the process simulation is embedded as a composite block in the control module. This approach allows the blocks used for control and the process simulation to be observed together in the same module. In addition, the parameters of blocks in the module, or blocks that make up the composite block, may be accessed and changed through this module as illustrated below.
From an engineering and maintenance perspective modifying existing control system modules is often not desirable. Thus, the most common means of adding process simulation to a control system is to create new modules that contain only the process simulation. These simulation modules may be added without modifying existing modules.
Most modern control systems include the capability for a module to read and write parameters contained in another module. Using this capability, simulation modules may read the output value of analog and discrete output blocks of an existing module. The results of the simulation modules are then written back to the simulation input parameters of the analog and discrete input blocks of the existing modules.
Examples of the how process simulation is used in the book workshops can be explored at the ControlLoopFoundation web site.