Implementation of a new distributed control system is one of the toughest projects undertaken by any process control engineer, with several complexities and risks. In order to do one successfully, the engineer must be well-versed in all steps involved, from documentation to grounding practices. Even though control engineers prepare themselves for such an implementation right from the start of their career, they often develop tunnel vision and find themselves stuck in a mesh of complexities. A couple of best practices regarding DCS implementation can help them navigate through common problems, ensuring that their project is a success.
Standardization
By using a standard wiring scheme throughout the implementation, it would be easier to carry out maintenance and upgrades. The use of standard, off-the-shelf components would allow future operators to stock and replenish supplies. Another possible addition would be purchasing products from two separate sources of vendors.
Ensure that you use proper grounding and termination for electrical signals. The supplier’s grounding requirements must be understood clearly and objectively. All automation engineers, and not just the electrical staff, need to understand the grounding principles. When international standards are followed, a supporting booklet and/or tutorials should be provided to ensure that misinterpretations do not take place in the future. Before powering up any part of the DCS system, be sure that there are no short circuits. This can be done during the Site Acceptance Test.
Several vendors use different software versions for communication purposes, ensuring that all data is transmitted. Several systems will transmit the basic parameters, robbing the setup of advanced diagnostics. A concept known as “Control in Field” can play a vital role here that transfers the control process from the central control unit for field devices. This gives sensors the autonomy to issue a response to an actuator based on the measured variable.
The I/O structures should be shifted away to the field that would cause a reduction in the cost and space requirements. The electronics manufactured today are usually resistive to high temperatures and may have G3 compliant conforming coating. Fiber optics should be utilized for communication links, preferably in a ring configuration to increase the reliability of the system. Extended I/O terminal blocks can be utilized for connecting the field working directly, avoiding additional costs and weak connections.
A DCS is designed to serve two purposes, to provide a centralized human control and a focal point for MIS information to the management network. Distributed Control Systems shouldn’t be burdened with tasks such as auto-tuning of control loops. Instead, such functions should be restricted to dedicated controllers.
To top it all off, before the shift-over takes place, make sure a detailed Factory Acceptance Test (FAT) is carried out that allows experienced operators to interact with the engineering functions of the DCS. This ensures that all functions operate the way they are expected to operate, and if any ambiguity exists it can be cleared straightaway.
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