Controls

Controls, variable speed drives, pressure reducing valves are a few examples of equipment that only operates during transient conditions such as start-up and shutdown and so these can only be studied and specified by using dynamic simulation technology.

One control company estimates that almost 60% of all control systems are not delivering the desired performance. Our experience confirms this and we believe that it is because many engineers lack the tools to design and specify good control systems and strategies. Our simulation programs allow our engineers to design and then test controls system before costly purchase and installation occurs.

Our senior engineers get to study the performance of many control systems each year and so have developed excellent skills in clarifying the requirement for the control system, (preparing the strategy) and then delivering simple, robust solutions. These solutions can even be tuned using computer programs and this avoids under-performance on site and reduces the commissioning time.

The industry is using more control, control valves and variables speed drives. The continuing programme to replace unnecessary service reservoirs and the growing need to save energy are just two compelling reasons to use control. Yet these controllers may not work effectively unless correctly designed and set-up.

 

The set-up of controllers is frequently misunderstood and many project engineers fail to understand the need to tune controllers and the attached equipment. So control bands (proportional, or proportional plus integral) need to be tuned to the exact situations. Valve opening and closing times needs to be set carefully to ensure stable control and variable speed drives must have a suitable ramp rate in order to deliver their potential.

Sometimes this ‘tuning’ is left to the commissioning stage, but this does not guarantee results because all of the equipment has been installed and so there is only limited flexibility for adequate set-up.

One client required a control system to perform during storm conditions and so could never test the system during commissioning. The system performed badly during the first storm and caused spills and commercial problems. Yet remedial measures could not be designed because the company could never get to work on the system during these storm conditions. Simulation can provide a non-intrusive method of designing and optimising control systems that allows even rare events to be considered.