How to choose a DCS system?

It is mainly determined based on the scale of the project and the investment budget. Theoretically, DCS can be used with various process technologies as it is a universal system; however, the manufacturers of DCS specialize in certain areas. For example, HOMEYWELL is mainly used in the petrochemical industry, while BAILEY’s N90 and INFI90 are primarily used in power systems. ROSEMOUNT’s RS3 and Δ-V are mostly used in the chemical industry.    However, it cannot be denied that different manufacturing processes have certain specific requirements; for example, power plants must be equipped with voltage regulation devices and SOE, the petrochemical industry requires selective control, and the cement industry needs compensation for large time delays in control systems. These factors also need to be taken into account when making selections. 　     The second point is cost-effectiveness, which should be considered from the perspective of the DCS’s price and the expected benefits it will generate.  There are domestic and imported DCS systems. For systems of the same category, imported ones have more advanced control functions, including sophisticated control algorithms such as Smith prediction and three-dimensional matrix operations. Domestic DCS systems are much cheaper than imported ones, yet they can still meet the technical requirements.   Structurally, the controllers of foreign DCS systems from different manufacturers differ little; the preset algorithms of these controllers vary slightly, and the way in which the controllers are connected to the I/O cards also differs. The operation stations, on the other hand, differ significantly. Some are based on PCs, while others are based on minicomputers; the operating system is generally a UNIX-based system. Minicomputers are much more expensive than PCs; imported minicomputer workstations cost over $40,000, and many models have been discontinued (such as DEC’s VAX and Alpha machines).    The operation station for PCs costs less than 30,000 dollars; it uses the NT operating system, and its stability is not as good as that of UNIX. The minicomputer uses SCSI for its interfaces, with a transfer rate that is 8 times higher than that of serial connections.   When using the NT operating system as the control station, the number of points required is lower; otherwise, frequent crashes will occur. Domestic PCs are much cheaper, and by using PC-based control stations, the latest models can be employed. Operators also have greater familiarity with software installation, debugging, networking, and development.    There are dedicated monitoring software solutions as well as generic ones; generic monitoring software offers better openness. Users should choose the appropriate option based on the scale of the project and the available budget.    In addition to the reasons mentioned above, another factor contributing to the high cost of DCS systems is the power supply system for the controllers; redundant power supply is typically used, and the process of supplying power as well as heat dissipation are the main reasons for the high cost. There are significant differences among various DCS systems in this regard. 　   The communication network that connects the controller and the operation station also needs to be taken into consideration; if standard Ethernet is used, network cards and similar components are inexpensive, while dedicated network interfaces are costly, with prices reaching up to $20,000.    Therefore, cost-effectiveness is related to many factors; sometimes when a foreign supplier lowers its price for you, it’s actually just a change in certain aspects of the structure, and no real discount is given – in fact, their profit may even increase.   A good approach at this time is to contact similar organizations in the country and seek advice from experienced experts.       The third point is the technical capabilities of the contractor, that is, how well the contractor is familiar with the specific process steps and the DCS itself.   If the contractor is not familiar with the DCS itself, a deadlock can occur when the controllers are made too large.   Many factories have purchased DCS systems from different manufacturers; we refer to this situation as the “Allied Forces” scenario. In such cases, it is better to choose a company with strong technical capabilities to take overall responsibility, rather than selecting a particular foreign manufacturer as the contractor. The fourth point concerns after-sales service: foreign manufacturers usually charge high prices for replacement parts and accessories, and they cannot provide them in a timely manner.    DCS users should choose manufacturers with strong backing, robust technical capabilities, and excellent domestic technical support.   Computer technology is developing rapidly, and DCS manufacturers also continuously update their products. It is essential that there be good compatibility between old and new products; otherwise, some manufacturers’ old and new systems are incompatible, which can result in significant losses during system upgrades.   Domestic DCS manufacturers provide components and spare parts in a timely manner, and also offer good after-sales service.     The fifth point concerns the technical advancement of DCS, referring to the use of proven cutting-edge technologies in the system, as well as its potential for further development and viability. This includes the openness and interconnectivity of DCS systems, the use of fieldbuses, and support from third-party software.   It is important to note here that in order to gain a foothold in the market, some manufacturers introduced immature products to the Third World. For example, around five or six years ago, DCS lacked small-scale systems, so some manufacturers supplied those immature small-scale systems to users; as a result, all of these more than 270 systems were taken out of service ahead of schedule.     As early as 1983, a DCS marketed by a foreign company exhibited arbitrary outputs from its controller after a power failure and subsequent restoration of power; this led to dangerous valve positions. Such products should not have been released for sale, yet they were still sold to us**. In practice, the units that purchased them hardly ever used them. In short, DCS systems have been in use for over twenty years now, and their reliability is generally satisfactory. When establishing a system, proper selection of the appropriate DCS is a very important step. We need to consider not only the scale of the project and the budget available, but also a range of other factors. Whether the right choice is made often determines the future success of the system from the very beginning, so it cannot be taken lightly. This post was last edited by sailonever on 2008-2-26 at 13:20.]

First, it is necessary to determine the level of the DCS – whether it is imported or domestically produced If the performance is similar, I think it’s better to choose the one that’s a bit cheaper, after all, it’s not easy to make money these days.

If the contractor is not familiar with the DCS itself, a deadlock can occur when the controllers are made too large. This is a bit hard to understand – the controllers are made too large; currently, Yokogawa from Japan makes them larger than those of other companies. Do they tend to crash more easily?

Looking at the CPUs, Yokogawa uses redundant fault-tolerance technology; it seems that HONEYWELL also uses this approach as well. With 4 CPUs in pairs for redundancy, the processing capacity is indeed very high. It shouldn’t be that easy to crash, right?

It depends on your device and process requirements. Due to the specific characteristics of various industries, different DCS manufacturers place different emphasis on the level of adoption in these industries. Therefore, when making a choice, it is necessary to take into account the specific requirements of applications in this industry, as well as the characteristics of various DCS manufacturers’ systems – such as special modules, specialized software, system response time, operating systems, and control methods – in order to select a DCS system that meets one’s own needs.