DCS system reliability research and field conditions - Solutions - Huaqiang Electronic Network

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I. Introduction

The main function of decentralized control systems (dcs) is to control, monitor, manage and make decisions on the production process. Therefore, it must have high reliability to ensure the safe and economic operation of the plant. With the continuous development of large-scale computer systems and computer communication networks, the reliability problem has become a very important issue, and its theory is constantly developing and perfecting under this situation. The research content of reliability technology is roughly divided into four aspects: reliability design, reliability analysis, reliability test, and reliability management.

Second, the reliability measures of the DCS system

In the DCS system, many technical measures to improve reliability have been adopted. These technical measures are based on the following four basic ideas: 1 to make the system itself less prone to failure, the so-called fault prevention; 2 to minimize the impact of the fault in the event of system failure, the so-called fault security and fault Weakening; 3 When the system fails, it can let the system continue to operate, so-called fault tolerance; 4 When the system fails, it can be repaired without stopping the system operation, so-called online maintenance. Based on these four basic ideas, various reliability measures are adopted in the DCS system to reduce the occurrence of accidents and the losses caused.

1. Strict quality management and improve system hardware level

In order to realize the hardware reliability of the DCS system, manufacturers of DCS systems have adopted a series of measures to improve hardware quality, such as strict screening of components, derating of aging components, full consideration of the impact of parameter changes, and low adoption. Power consumption components, noise suppression technology, etc.

2. Reliability measures for DCS system site design

After the DCS has a problem, there will be cases where the device is out of control due to inoperability and unmonitoring. In the case of light, the outage of equipment affects economic benefits, and the serious ones endanger the safety of people and equipment. Therefore, in the design, we must carefully consider the following reliability of the system according to the specific conditions of the site:

(1) Power system

The power supply system of the DCS system is the basis of its operation, and the power supply load should not exceed 60% to avoid high-load operation of the power supply. At the same time, we must consider the use of high-quality power supply. Generally, the author uses the ups power supply. It is best to use two UPSs for each other. After a fault occurs, the backup machine can be switched without interference, improving the reliability of the power supply. Do not use the same busbar of the UPS input power supply. According to the wiring of the electrical plant, take the different busbar power supply with high reliability. This will ensure that the power supply of the DCS system will not be affected after the electrical bus has a problem. DCS power system (UPS, power cabinet, etc.) should be installed in the electronic equipment room that meets the requirements of dust-free, vibration-free, anti-corrosion, etc. when installing on site. At the same time, the cable hole is sealed before installation to prevent leakage of steam from the cable. The hole enters the power system and causes a short circuit in the power supply. After the DCS power supply is powered on, it is necessary to hang the "device live operation prohibition operation" sign on the UPS, power cabinet, etc., and it is not allowed to connect the DCS power system to the load unrelated to the DCS system, such as maintenance power supply, overhaul Lighting, charging equipment, air conditioning, etc.

(2) Redundant system

On-site considerations necessitate redundancy of important I/O modules, taking into account the N:1 redundancy structure of the operator station, thus avoiding equipment outages due to hardware failures in the card or operator station.

(3) Adopting backup measures

1 manual backup

For important control loops, manual backup methods can be used to increase reliability. Once the automatic control fails, use the manual operation station to directly operate. In this case, the manual operation station directly outputs 4~20mA or 1~5V analog signals to control the actuator or directly ground the device for operation, which can be manually controlled. production process.

2 automatic backup

Automatic backup is to set up another set or sets of spare control devices in a redundant manner. When the automatic control device in the running state fails, the standby control device automatically inputs to maintain the automatic control of the system. Automatic backup is a form of redundant system with redundancy of main control unit redundancy, power system redundancy, network redundancy, I/O module redundancy, operator station redundancy, and server redundancy. When the running equipment fails, the hot standby equipment will automatically and uninterruptedly operate without affecting the repair of the faulty equipment.

3, in a safe state when the system is faulty

The DCS system itself continuously performs online fault detection during operation. Once a fault is found, the faulty device is isolated from the system so that it does not affect the normal operation of other devices. After the fault occurs, an audible and visual alarm will be issued at the same time. The maintenance personnel will analyze the cause of the fault according to the prompt of the alarm and deal with the fault as soon as possible to avoid the fault from expanding. In the process of processing, you should do a good job of on-site technical measures, do not easily restart the CPU, so as not to cause disturbance to the device. If you need to restart the CPU, you need to cooperate with the operator to take precautions. Generally, the DCS resets the analog output signal when the CPU is reset. This allows manual switching control of the actuator and inverter. The actuator can also be used. Electrical mode or unplug the analog output card (actuator has a break signal hold function), after the system is normal, add the signal to the normal value and then power on the actuator and the card. However, it must be carried out according to the characteristics of the DCS itself. In some designs, there is a switch safety output (on, off, hold, etc.). If the safety output selected by the user during configuration is on, the switch will be issued when the CPU is restarted. Open instructions.

Third, the site conditions

1. On-site environment

The DCS system is generally placed in the control room or in the computer electronics room. The computer room should be insulated and dustproof. It is also necessary to avoid interference from strong electromagnetic fields and away from strong vibration and strong noise. The net height of the computer room should not be less than 3.2m, the area should be no less than 20m2 (one computer and its peripheral equipment), and there should be an electrical socket in the room. The floor should be smooth and non-static, and the floor should be raised with a raised floor. The height of the lower space should be no less than 150mm. The computer room should ensure that the indoor temperature is in the range of 18 to 25 ° C, the temperature change rate is less than 5 ° C / h, the relative humidity is in the range of 45% to 70%, and condensation is not allowed under any circumstances. When the air conditioning equipment fails, the room temperature should be maintained within 24 hours without exceeding the manufacturer's permissible value. The above conditions need to be strictly controlled before the DCS system is powered on. The working environment is the basis for ensuring reliable operation of the equipment. If the environmental requirements are not met, the DCS system will be affected to varying degrees during operation, such as high temperature and high humidity. The vibration and the like will affect the normal operation of the DCS system.
2, cable laying

(1) The inner connecting wires of the control panel, table, relay cabinet, etc. should be made of copper-core PVC insulated wires. For the connection line of the plug-in (or the connection line of the FK type switch), a copper-core PVC insulated cord should be used.

(2) Thermocouple to cold junction compensator, incubator or direct connection to the instrument, the thermocouple wire extension wire or the compensation wire matching the thermoelectric characteristics of the thermocouple wire should be selected.

(3) The analog analog input signal and the low level switching signal should be connected by shielded cable. The cross section of the signal cable core should be greater than or equal to 1mm2. The high-level (or high-current) switching input and output signals can be connected by a common twisted pair cable (control cable), but should be separated from the analog signal and the low-level switch signal to separate the cable slot.

(4) Weak signals and low-level signals, especially those requiring anti-interference signals (such as computers and phase-separated instrument converters), should not be combined with a strong electric circuit or a cable or laid in the same protection tube.

(5) Cables with different signals or different voltage levels should not be laid in the same layer of brackets; when laying in the same layer of brackets, they should be arranged in a sorted manner and separated by partitions if necessary.

(6) It is forbidden to lay the cables in parallel above the oil pipeline or directly above the gas pipeline and under the oil pipeline interface.

(7) The input and output signal cables of the computer should be laid in the cable trough with cover. The cable channel and cover should be well grounded. A single signal cable should be laid in a steel cable tube, and the cable tube should be well grounded. The cable shielding layer should be shielded with copper tape or aluminum foil.

3, the site grounding common precautions

The DCS system has strict requirements on grounding. When grounding in the field, it must be strictly grounded in strict accordance with the grounding specifications of DCS manufacturers. Otherwise, the reliability of the DCS system will be affected. Pay attention to the following points when grounding the DCS system:

(1) The power ground of the I/O cabinet must be connected to the same ground as the power supply ground of the UPS to ensure equipotentiality.

(2) The grounding cable must meet the requirements of the DCS manufacturer and be connected to a dedicated grounding screw in the cabinet.

(3) System grounding and shielding grounding cannot be combined in the cabinet and must be separately connected to the grounding grid.

(4) The cabinet cannot be replaced indirectly by the cabinet and the bolts must be connected strictly by the grounding wire.

(5) The grounding should be firm and reliable, and the connecting plate should be coated with anti-corrosive paint.

(6) The grounding resistance complies with the DCS system requirements and requires rigorous measurements.

(7) Grounding is strictly in accordance with the grounding requirements of DCS manufacturers. It is not allowed to take shortcuts or to follow the grounding wire diameter requirements. #p#分页头#e#

The grounding of the DCS system does not meet the requirements. In the course of operation, unpredictable faults may occur, such as signal acquisition errors, abnormal communication, computer crash, control failure, and protection misoperation.

Fourth, system maintenance

The following points are summarized for DCS system maintenance:

(1) Regularly check the power supply of the DCS system. For the redundant power supply system, the switching experiment should be performed periodically. At the same time, the UPS power supply is periodically switched and checked, and the battery is periodically discharged and charged according to requirements.

(2) Regularly check whether the network connector and each cable are secure, and whether the terminals in the control cabinet are secure and reliable.

(3) Always check whether the control unit, I/O module, other modules, etc. work normally.

(4) Regularly check that the grounding is secure and test whether the grounding resistance meets the requirements.

(5) Regularly check the workload of the controller, computer, etc., and pay attention to whether there is an increase.

(6) Regularly check the MMI hard disk and delete the fragmented files. The history files are often backed up by the peripheral archive.

(7) Reset the DPU (Distributed Processing Unit) and MMI (Human Machine Interface) of the DCS system one by one during the maintenance period of the unit to eliminate the accumulated errors of long-term operation of the computer.

(8) For the interface between DCS system and other systems (such as MIS (Computer Management System), SIS (Factory-Level Monitoring Information System), etc.), it is recommended to install a virus firewall on the gateway station of other system side, and update the virus in time. Library. At the same time, update the operating system patches in time to improve the security of the system.

(9) Regularly check whether the system fan is working properly and the air duct is blocked to ensure the system can operate reliably for a long time.

(10) When the unit size is down, pay attention to check the power of the DPU host card COMS battery. When there is a loss of COMS data due to the lack of power in the COMS battery, the COMS battery of the motherboard should be replaced in batches.

(11) Regular inspection habits, regular inspections, and regular cleaning to ensure that the DCS system operating environment is clean and clean.