1. Communication network failure: communication network faults are generally easy to occur at the contact bus and local bus, or caused by wrong address identification.
2. Node bus failure: The transmission medium of the node bus is generally coaxial cable, some use the token signal transmission mode, and some use the multi-channel transmission bus signal transmission mode with conflict detection. Either way, an interruption at any point on the trunk of a bus will result in a communication failure for all stations on that bus and their sub-devices.
3. Local bus failure: The local bus or fieldbus is generally a data communication network composed of twisted pairs. Because the connected equipment is a primary element or control equipment that is directly connected with the production process, the working environment is harsh, the failure rate is high, and it is easy to be affected by the malfunction of maintenance personnel
4. Error of address mark: Whether it is a local component or a bus interface, once its address identification is wrong, it will inevitably cause disorder in the communication network. Therefore, it is necessary to prevent the failure of the address identification of each component, and prevent human misoperation and alteration.
5. Hardware failure: According to the different functions of each hardware, the failure of DCS system can be divided into man-machine interface failure and process channel failure.
6. Human failure: In the maintenance or fault handling of the system, sometimes human misoperation will occur, which will occur for personnel who often carry out system maintenance or newly participate in system maintenance. Generally, when modifying control logic, installing software, restarting the device, or forcing the device, the protection signal is the most likely to misoperate.
7. Power failure: there are many problems in the power supply, such as the standby power supply can not be self-invested, the unreasonable insurance configuration and the internal fault of the power supply cause the power supply to be interrupted, and the fluctuation of the stabilized power supply causes the protection malfunction and the poor contact of the plug leads to the no output of the stabilized power supply; In some systems, the entire cabinet is supplied with a safety supply for all input signals or a power supply, and the external load is large, and the control power supply is neither connected nor redundant.
8. Failures caused by interference: There are many cases of failures caused by interference. The interference signal of the system may come from the system itself or from the external environment. Because different systems have strict requirements for grounding, once the grounding resistance or grounding mode does not meet the requirements, it will reduce the efficiency of network communication or increase the possibility of bit error, which will cause some functions to be abnormal, and cause network paralysis.
DCS communication fault prevention measures
01 Do a good job of backing up data in a timely manner
To regularly and timely backup DCS configuration software, PID parameters and various application software data, etc., the backup can use mobile hard disks, U disks, etc., but it is best to use DCS special memory. When the DCS system needs to optimize and change the test points and logic during operation, the configuration must be backed up in advance, and the system must be recorded in detail, such as the PID parameters of each control loop, the positive and negative effects of the regulator, etc.
02 Reasonable arrangement of hard-wired input/output
In order to minimize the data exchange between different I/O stations of DCS, it is necessary to make scientific and reasonable changes and arrangements to the hard-wired input/output to prevent information transmission blockage caused by excessive transmission load, so that the DCS communication system has abnormal phenomena such as untimely and inaccurate information transmission.
03 Strengthen training and standardize operating procedures
When carrying out DS system maintenance, it is necessary to standardize the operating procedures, because some work has greater potential safety hazards, and relevant staff should be trained by relevant work experience to prevent DCS communication failures caused by human factors. For example, when uninstalling the application software in the system, changing the control parameters and modifying the human-machine interface, it is necessary to operate in strict accordance with the relevant regulations, which can effectively reduce the possibility of DCS system failure.
04 Ensure that there is no source of electromagnetic interference
Electromagnetic interference will affect the stability and reliability of the DCS system, so it is necessary to ensure that there are no sources of electromagnetic interference around the DCS system. It is strictly forbidden to use walkie-talkies, mobile phones and tablet computers and other instruments and equipment that can generate electromagnetic waves in the cabinet room to avoid generating interference signals and causing system copper communication failures.
05 Strict design of controller and communication network load
In the design stage, the workload of the DCS controller should be strictly calculated and standardized, and the communication network load should be carefully calculated, and the redundancy of I/O points and the number of alarms should be taken into account when the design is changed. At the same time, before the formal operation of the system, it is necessary to carry out debugging and trial operation, simulate various emergencies that may occur, find out the communication failures in time, and prevent unnecessary economic losses after operation.
06 Establish a scientific and reasonable DCS maintenance management system
DCS maintenance personnel should check the working status of DCS cabinets and communication network modules on time every day, check whether fault prompts occur, analyze the causes of abnormal situations in time, and deal with them in time. Check the hardware working status of the network with a network tester, as well as check the indicator lights of the switches, use the "ping" command to check the computer network, and the IP settings of each computer. When inspecting the card and communication parts, wear an anti-static wrist to prevent communication failure caused by static electricity.
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