1. Assign measuring points
Check out the special requirements or equipment first, and then configure the general equipment after processing. This will improve efficiency and prevent misoperation. Here are a few principles for configuration of general DCS system equipment.
The same measuring points should be allocated on different DCS system cards as much as possible. This is to spread the risk. If a module is replaced or malfunctions, another module can also monitor the same measuring point.
The same equipment should be allocated in the same DCS control station as many as possible. This distribution is to minimize the data link between stations and reduce complexity and points of failure.
If there is a variable exchange between the stations of the DCS system, it is best to use hard wiring. This approach is also to enhance the stability of the system, but there are some disadvantages, because this takes up at least two DCS system card channels , One AI input, one AO output, so it can be considered according to the situation. If there are many variables that need to be exchanged, the only way to use network variables is to complete data exchange through the functions of the server computer software.
Each DCS card module should have 2-4 spare channels. In order to adapt to the changes of the system, because if users add measurement points or swap from broken channel, and cannot find the channel, it will bring a lot of trouble to our work, so this is necessary to have spare.
There should be have spares for each type of card in each control station. This is for the convenience of maintenance consideration: if the card fails, the problem can be solved by replacing a new one by hot plugging in the first time.
Add four identification for each wire in the database, controller/cabinet number, module number, channel number and signal description, so that each data point is allocated to a different channel of a specific module without duplication and easy to find the signal wiring.
According to the characteristics of the control system, each control station has a certain load capacity, which means that the number of modules that can be connected is limited. Therefore, it must be divided into several control units and cabinets.
Before submitting the final configuration results, must carefully "go through" the above work. It need to re-verify every step. When the database is organized is some data hidden due to misoperation? Or accidentally deleted? Did mess up the data when sorting? Compare the system diagram to find the position of each point in the database. Finally, according to the distribution principle, recalculate whether the configuration is reasonable and whether it meets the requirements.
2. Complete the DCS system hardware configuration according to the number of I/O points
The hardware configuration of the DCS system of different brands is not necessarily the same, but the configuration ideas and methods are the same: DCS system hardware is determined according to the exact requirements of the site and the number of DCS system I/O points . The DCS system hardware configuration needs to complete the following:
Hardware redundancy configuration
Redundant configuration of key equipment is an important means to improve the reliability of DCS. DCS system redundancy usually includes power supply redundancy, controller redundancy, communication redundancy, operation station redundancy and DCS system I/O board redundancy. For specific redundancy requirements, it is best to communicate carefully with the DCS system manufacturer, and do a good job of redundancy configuration and statistics on the number of related equipment.
The configuration of the connection
Configure server connection, power connection, I/O connection, communication connection and other hardware devices according to system requirements and control scale;
Confirm the number of cabinets of the DCS system
The DCS system cabinet is used to put and install the DCS card module. The configuration requirements of the DCS system cabinet of different manufacturers are different, but the corresponding cabinet is basically configured according to the number of cards that has been determined. The DCS cabinet is used to house various connection, DCS card module and intermediate relays. The common size of the DCS cabinet is 2100*800*600mm.
Hardware installation
Different DCS, for the installation of various connection, there will be according to the requirements in logical or physical order.
3. Assign operator station
In general, each main production equipment is equipped with an operator station, so this application is equipped with 4 operator stations, plus an engineer station. Some systems need to be equipped with redundant servers, so it should choose a higher configuration computers, and printers should be equipped if necessary. When it is necessary to communicate with other systems, it should be equipped with corresponding communication equipment, such as serial port cards. In order to prevent other equipment from interfering with and damaging the main control system, most of them use communication methods for data exchange, which means that other systems cannot be connected to the main system.
4. Draw network system and power distribution diagram
After confident that the previous work has been completed, start the next step, drawing the power distribution system diagram and network system diagram. The content of the power distribution system diagram includes the details of the power supply and grounding system of the entire control system, including the power entering the system, the power wiring principle in the system, and the system grounding principle. This is a very important content, because after the equipment arrives on site, the power supply is connected by the construction team. Whether the power supply is stable or not directly affects the stable operation of the system. Generally, the system is a two-layer network connection. The network location and IP address of each computer must be described. If there are other connection methods, it should be clearly pointed out. The network system diagram can also include the module distribution diagram of each control unit, which is used to indicate the specific location of each I/O card and the bus connection mode of the front-end data collection.
5. Terminal wiring diagram
Don’t forget another important drawing, which is the I/O terminal wiring diagram. This part of the drawing describes the signal content of each channel in each I/O card, as well as how to wire it. The construction personnel determine the direction and length of the cable according to the distribution position of the measuring point. They can also combine the signals of adjacent positions into one cable. Therefore, we can see that a reasonable design can not only ensure the integrity of the system function, but also can save a lot of materials and man-hours, this is depend on design experience.
The characteristics of this stage are complicated and require concentration. Because it easy to cause trouble to the subsequent work, it is not easy to track the error, and sometimes leads to fatal errors. Therefore, the author recommends to find and read some DCS construction project that already finish from the beginning of the design. Study each step in detail to get better understanding about each process.
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