DCS system is a decentralized control system that combines modern high-tech technologies such as computer, display, communication, continuous monitoring, alarm, and programmable control. It has comprehensive functions, convenient operation, flexible configuration, and stable reliability. Practice has proven that the application of DCS systems in large and medium-sized production enterprises not only helps with daily production maintenance and reliable and stable operation, but also saves expenses for enterprises, thereby reducing costs and improving their core competitiveness.
Common faults in DCS system
1.1 Communication Failure
There are various network topologies and communication protocols used in DCS systems, but different brands of DCS systems in the market are mostly divided into two levels in terms of network organizational structure: one is towards the central processing unit and its expansion sub stations (lower level computers), and the other is the human-machine interface, such as various stations (upper level computers) of operators, servers, and operator stations. Communication failures usually manifest in several forms: system crashes, network disconnections, communication interruptions, and so on. There are three common reasons for communication failures: firstly, the operation of DCS system communication functions is mostly completed by asking data from one node to another node. If the other node does not have the data, it will ask again and again until it reads the data. If the data is not available online, the network will be blocked and communication cannot proceed normally. Secondly, DCS configuration is lacking, and its application software has been increasing with the development of technology. However, it is not actually connected to I/O points. Therefore, even if the CPU reads data, there are very few effective ones, which puts a considerable load on the CPU and can easily cause network congestion. Finally, factors such as network communication media issues, hardware upgrade drivers not keeping up, high operating environment temperatures, etc. may all cause obstacles to communication.
1.2 Hardware Failure
Hardware failures generally manifest in the process control layer, mainly in the modules of the entire system, especially in the case of I/O damage. Hardware failures can be very obvious, so they are relatively easy to detect. The impact they bring is usually only local, and if the parameter display does not change, it is a manifestation of hardware damage. Hardware damage is often caused by improper use or prolonged use, leading to aging of components. If the surrounding environment of DCS is dusty and high-temperature, it will seriously shorten its service life. Considering this, it is best to ensure that the civil and decoration projects have been completed before installing the DCS control system. If it is in summer, it is also important to turn on the air conditioning in a timely manner. When selecting DCS system products for complex environments, the protection level should be given special consideration. At present, many brands of DCS products in the market have developed hardware self diagnosis functions, which can directly reflect the location of the faulty hardware on the upper computer, and can also pinpoint which channel has malfunctioned, bringing a lot of convenience to troubleshooting hardware faults.
In addition to channel faults, there are also human-machine interface faults in hardware faults. Specific manifestations of human-machine interface faults include: the mouse cannot operate normally, and because it fails, it is very inconvenient for operators to use. The reason for this situation may be the instability of the USB interface, or it may be a problem with the computer motherboard. The crash may be due to defects in the DCS system software itself, or it may be caused by excessive CPU load. When this situation occurs, it is important to patiently analyze the cause. The function keyboard operation fails, and sometimes there may be poor key contact, which can cause abnormal keyboard operation.
1.3 Software Failure
Software failures are usually caused by defects in the DCS system itself, mostly occurring in the early stages of DCS software upgrades. Software is the most complex part of the DCS system, with complex programs and often cross functional tasks for configuration workers. As a result, once communication is not in place, vulnerabilities will occur and software errors are inevitable. The modification of DCS system software needs to be strictly carried out in accordance with regulations, and backup should be made for the modification. In case of data loss, backup can be used for repair. There are three main types of software failures: the configuration information of the main CPU and the slave CPU is inconsistent, causing the CPU to be unable to complete initialization; Excessive network communication pressure causes system chaos; After a component update, the relevant parameters did not change accordingly.
1.4 Power failure
A power failure can directly lead to the malfunction and cessation of operation of DCS system controls, causing economic losses. Controlling the power supply is not an exaggeration to say, the lifeline of DCS system. If some particularly important power supplies fail, it will directly affect the orderly and stable operation of protection logic and other control logic, and even lead to the misoperation of some interlocking driving components, causing serious production accidents. Common faults in power supply include: (1) loose or unstable crimping of the wiring head, resulting in poor contact; (2) CPU issues or improper safety configuration, resulting in power interruption; (3) The wiring of power lines lacks scientificity and is too close to facilities with strong magnetic interference; (4) Various reasons lead to module damage.
2 Preventive measures
2.1 Anti signal interference
Even minor signal interference can cause communication failures, affect system operation, cause system paralysis, or directly interfere with signals entering DCS, resulting in misoperation and other significant losses. To better resist signal interference, it is necessary to install a dense layer of steel wire mesh before painting the walls around the central control room, and then connect it to the PE grounding system, which can effectively avoid the huge interference of strong electromagnetic fields. Secondly, it is best not to connect power equipment in series to ground them, and to keep the power equipment as far away from the grounding wire as possible. Thirdly, a dual loop redundant power supply system is adopted to power the DCS, maintaining uninterrupted UPS power supply and improving the overall anti-interference level of the power supply and circuit. Fourthly, all analog signals entering the DCS system must be connected with shielded cables, and the shielding layer must be properly grounded with a ground resistance of less than 1 Ω. Fifth, try to shield the radio around the DCS system as much as possible.
2.2 UPS power supply maintenance
Regularly use an infrared thermometer to measure the actual temperature of key wiring terminals, and record it in detail. If there is any temperature rise, be extra careful; Use a multimeter to measure the power supply voltage and record the data. If there are fluctuations, be extra careful; During the maintenance or shutdown phase of the DCS system, timely switch experiments should be conducted to monitor whether the redundant CPU can automatically switch and be in normal working condition; Check the I/O modules, and replace some aged and corroded electrical connectors in a timely manner; Strictly follow the battery usage rules for charging or discharging; Inspect the fan and clean it if necessary to ensure that the air duct is unobstructed.
2.3 DCS software and hardware system operation and management
2.3.1 Operation management. The so-called operation management refers to daily inspections, software management, spare parts management, and so on. Software is the core of the DCS system, and the program is complex. Its configuration and modification must be executed according to regulations, and the modification information must be backed up to prevent faults caused by data loss; If there is a problem with the DCS device, it needs to be replaced with spare parts. Before installation and use, it is necessary to conduct a comprehensive test of its function to avoid the recurrence of the entire system failure.
2.3.2 Maintenance management. Maintenance management attaches great importance to maintenance processes and procedures. In order to ensure the stable operation and quality of the DCS system, and to operate normally for a long time, regular major maintenance must be carried out at regular intervals, such as software backup, power cleaning, component cleaning, etc.
With the development of technology, DCS control systems are becoming increasingly mature and perfect, and are widely used in various industrial production fields, becoming indispensable self-control equipment. The powerful functions of DCS have brought huge economic benefits to industrial production.