DCS Control System

A correctly designed DCS control system is essential for the safe and efficient operation of a process plant. Process Technical Services can provide qualified and experienced instrument and control system engineers and technicians that will review the P&I diagrams in detail to determine if the DCS control system will meet the needs of your operations.

Particular attention is to be paid to DCS control system feed-forward, feedback, and cascade control systems. Although final tuning of DCS control system controllers can only be done with the plant in operation, the initial setting of the controller tuning coefficients is essential for a smooth start-up of the process. PTS engineers and technicians utilize results from dynamic model simulations, process flowsheets, and equipment sizes to estimate the impact of dead-time and equipment holdup times on DCS control system tuning coefficients for the various processing units throughout the process.

The process variables sent to a DCS control system include pressure, temperature, level, and flow sensors. PTS' qualified and experienced instrument and control system engineers and technicians can provide valuable insights and consultation regarding the reliability and accuracy of a variety of sensors. Their advice may help avoid installation of field instruments of questionable reliability and accuracy during the installation phase of a project and possibly avoid countless hours of poor operation, upsets and downtime after the process is commissioned.

PTS’ experienced instrument technicians can pre-commission DCS controls and provide a preliminary set of parameters that will provide for a smoother and more orderly start-up of process units utilizing accurate P&IDs.

Essential DCS control system elements in most modern process control system designs include on-line and in-line process analyzers. An on-line analyzer is one that processes a sample extracted from the process and thus requires an automatic sampling system to extract material from the process for analysis such as a gas chromatograph (GC). Another method is the use of an in-line process analyzer with the sensor inserted directly into the process material. A pH probe is an example of an in-line analyzer. Another type of in-line analyzer might require a side stream that causes process material to flow through a small bypass line.

It is important that the process design criteria specified by the DCS control system engineers be strictly followed during the procurement process. There is a strong incentive for the equipment purchasers to buy from the lowest qualified bidder, but one who has not necessarily met all of the design criteria. This can be a particular problem with process control valves. PTS control system quality assurance (QA) technicians can insure that all control system equipment being purchased meets all of the design specifications.

Finally, even with a good design, and equipment that meets all the design specifications, there is still one area of activity where problems can develop. That is during the installation phase. Experienced and professional PTS Quality Control (QC) technicians can monitor the installation process from start to finish ensuring that the DCS control system installation follows industrial standards and meets all of the design specification.