1. About dispersion of faults:  It is believed that the systems provided by most of the DCS system manufacturers at present have no such "dispersion of faults" in practical application. In fact, because of some problems of DCS system existing in application technology,  it is common for one generating unit of thermal power plant controlled by DCS system to be forced to shut down due to some faults of DCS systems. Compared with traditional instrument control system, the latter seems to be better than the former in this point. For this reason, the closer the composition of DCS system is  to the traditional instrument control system, namely the more the control tasks undertaken by microprocessor or multi-functional controller are dispersed geographically , the better the dispersion of faults can be done. From this point of view, SIEMAMS system can do much better, its one piece of control card parts (with microprocessor, which can be communicated with other cards or communication busbar as well as other subsystem, such as operator station and engineer workstation) can only undertake open-loop circuit for 2 ~ 4 motors or the electric door , and this card not only can undertake the logic control function, but also can undertake I/O functions related with these logic control. It is very beneficial to do this for the dispersion of faults. However, other systems usually concentrate many process control tasks on a few of multi-function control cards or microprocessors, and concentrate the function of input/output( I/O) on  I/O card. Objectively these systems concentrate the faults of process control, rather than disperse them, which seems to be contrary to the name  of "DCS". But SIE - MANS system also has a problem, there are some problems in communication between its ETHERNET with ME system that shall be solved. TELEPERM - ME system of SIEMANS is a very mature system, the ME system and ETHERNET network are the latest TELEPERM - EM/XP system, because it is a new system, it is believed that many applications, (especially those related to communications software) shall undergo the test of time. If these problems are resolved,  then whether from the angle of dispersion of faults or other aspects, such as the manufacturing process, this system has occupied a certain degree of advantage.DCS and dispersion of fault, it seems that SIEMANS is on the correct way, because their system is the  instrument control system closest to the traditional instrument control system, the control functions are more dispersed. If the faults shall be dispersed, the control functions must be dispersed.

2. About the size of the control room and the length of dial: This can be realized by all DCS systems. But compared with the traditional instrument control system, the size of electronic chamber and equipment shall be relatively increased, in this point, the real interest brought by DCS system bring is not significant.

3. About saving cables. The equipment and device  adopted by DCS system at this stage are still more delicate, they have higher requirement on site environment, for example, they shall be dust-proof and air conditioned, and REMOTE I/O cannot be used in great quantities, therefore, the main equipment of DCS system shall be placed in electronic chamber with better conditions, a large number of field signals shall be connected to the electronic chamber via cables. So, compared with the traditional instrument control system, the cables are reduced, but the efficiency is limited. 

4. About cutting down on the amount and type of spare parts. There is a decrease in the amount and type of spare parts, and the instrument control equipment manufacturers related with spare parts will be reduced too.

5. Regarding the relying of the operation of unit on the instrument control equipment manufacturers and the cost required by the technical training to the instrument control personnel.DCS system in application technology is still not satisfactory, as a result, the relying of operation of unit on DCS system manufacturers not only has not been reduced, but also it is increased, especially during the period of commissioning of the unit newly built, the services of experts sent by DCS manufacturer to the site seem to be essential during test run and commissioning. In order to well use DCS system, the project technical persons to be trained are also increased, so the training expenses are also increased.

6. About the  flexibility of the composition of control system, the convenience of configuration and the extendibility of the system. The flexibility of the composition of control system and the extendibility of the system cannot be matched by traditional instrument control system. The configuration of most of the DCS systems is also more convenient. However, as for most of the systems, many work shall be done in configuration, many systems are configured in off-line state, programmed in the engineer station, then are compiled and downloaded. And some systems take time in this process, it is especially prominent during debugging. About this question, SIEMANS system is distinctive, it not only is configured on-line, but also has simulation function in design, which brings great convenience to debugging.

7. DCS system provides some unique control functions, such as historical data and real-time data management, performance calculation and so on. This is what the traditional instrument control system cannot compare, it is just because of these advantages of DCS, and the process control has been pushed to a new field of higher level.

To sum up, at this stage the advantages brought by DCS system in the application of DCS system provided by the market is far from the much that we imagine. Of course, DCS system can solve the problem in production process of modernization that the traditional instrument control system is difficult to competent, and for the central control of computer, the faults are dispersed, in many aspects DCS system has its unique advantages, which cannot be matched by the traditional instrument control system and the centralized control system by computer.