How to judge whether the DI card of DCS system fails in time?

Q 1: What are the control system problems or process problems? A: When the following situations occur, it means that there is a problem with the control system, and the microcomputer maintenance personnel should be notified immediately for maintenance, and the operator will go to the scene to deal with it. 1. Frequently changed data remains unchanged for a long time, and several or all data remain unchanged. 2. In the control grouping screen, it is impossible to switch between manual and automatic, or once the data is manually entered, it will be restored to the original data and cannot be modified. 3. In the trend chart screen, several trends are straight lines. 4. In the monitoring screen, a number of data fluctuate greatly at the same time.

Judge whether the fluctuation data is the relevant parameter in the process. If it is a related parameter, notify the instrument and microcomputer personnel to check whether the fluctuation of the regulating system causes the change of the related parameter. At the same time, set the relevant adjustment system to manual state, and go to the site for adjustment when necessary. If the fluctuation data have no direct influence on each other technically, it may be that a card of the microcomputer has failed, so the relevant self-adjusting system will be adjusted manually immediately, and the adjustment will be made on site if necessary, and the microcomputer and instrument personnel will be notified for inspection. Q2: How to power on the DCS system after overhaul, and how to check the power supply of DCS? A: DCS system has certain requirements for power supply quality. Pay attention to 1 when powering on DCS after maintenance. Confirm whether the external power supply is stable. If the voltage is unstable during maintenance, please do not power on. 2. Test whether the external power supply voltage meets the requirements of 198V-242V. 3. When power is on, first turn on the main power supply, and then turn on the power supply of the operation station, control cabinet and external distribution cabinet in turn (the opposite is true in case of power failure). 4. After electrifying, check the DCS card fault alarm, voltage fault alarm, switch and network, and test the power supply voltage. 5. Use a multimeter to check the 5V and 24V voltages of each cabinet of DCS. If it is lower than 5V and 24V, it is abnormal. If it is necessary to check the power supply quality in depth, it is necessary to use an oscilloscope or power quality analyzer for detection and analysis. Expert's suggestion: the person in charge of system maintenance can only power on when the conditions are met. Power-on procedures should be strictly followed. Q3: What should we pay attention to in the daily management of the central control room? A: The daily management of the control room is very important for the stable operation and maintenance of the system. Pay attention to daily management: 1). The doors and windows of the control room are arranged reasonably, and the operation station, control cabinet and UPS are placed in a standardized manner with clear marks. 2) Keep the control room clean every day, maintain proper temperature and humidity, and check the operation of lighting and air conditioning. 3) Check the waterproof, dustproof, anti-corrosion and anti-vibration conditions of the system every day, and rectify the loopholes in time. 4) Standardize management. Irrelevant personnel are not allowed to touch the card in the control cabinet, and the operating station is provided with a password to strengthen safety management. 5) Check the identification of switches, terminals and external accessories in the control cabinet to make the identification clear and easy to maintain. Expert advice: the temperature range of the control room is 0-50 degrees Celsius, and about 20 degrees is appropriate; Humidity range: 10%-90% RH, no condensation. Q4: How to know the current fault situation of DCS system in daily maintenance? A: It is very important to pay attention to observation during daily maintenance. The key points of observation and understanding are: 1, whether the card indicator light of the control station is abnormal (whether the fault light is red), and 2. Enter the monitoring "fault diagnosis" screen, and check whether there are card operation fault prompts and communication network abnormality prompts. Check whether the system power supply is normal. 4. Check whether the power supply fan of the control station is running, whether the switch indicator light is normal and whether there is corrosion (whether the connector or the copper bar of the cabinet is black, etc.). ). Q5: How to simply check the grounding of DCS system?

A: DCS grounding is a very complicated problem, involving many nodes and links from the site to the DCS cabinet, such as grounding location, grounding mode, grounding resistance and so on. However, the routine inspection of DCS mainly includes several aspects: 1, the DCS cabinet should be grounded at a single point, and check whether there is any place that may lead to multi-point grounding, such as the contact between the cabinet and channel steel, whether the grounding point is a single down lead of grounding pile or grounding grid (the line diameter is greater than 16mm2 and the length is less than 30m), and whether the connection (or welding) points of components are good (corroded). 2. Check whether the grounding point of DCS is used together with electrical grounding or lightning rod downlead, and whether the distance meets the requirements. Generally, the distance between DCS grounding and electrical grounding is greater than15m, and the grounding point between DCS and lightning rod is greater than15m. 3. Measure whether the grounding resistance of DCS system is less than 4 ohms. The size of grounding resistance is related to many factors, such as good contact, soil moisture, conductivity and so on. The instruments for measuring grounding resistance are shaking table and clamp table. Q6: How to check the DCS system network during routine maintenance? A: 1. Use the network tester to test whether the network cable hardware is normal and check whether the switch indicator is normal. 2. Check and monitor the "Troubleshooting" screen to see if there is a fault prompt. 3. Use the "ping" command for each computer to check whether the network is normal and the IP settings are correct. 4. Check whether the network card flow control is turned off and whether the network card driver is installed normally. 5. Use the SCDIAGNOSE software that comes with the configuration software to detect the network status. Q7: How to prevent static electricity in DCS system maintenance? Answer: If you don't pay attention to maintenance, static electricity may have a great impact on DCS card or communication. During the maintenance of DCS, especially when contacting hardware cards or communication components, the following measures should be taken to prevent static electricity. 1, keep the environment with a certain humidity. Especially in the northern area or dry winter, the cases of electrostatic failure are far greater than those in the southeast coastal areas or other seasons. Therefore, in some important places, such as computer rooms, laboratories and electronic instrument assembly and adjustment workshops, the problem of maintaining a certain humidity should be considered, especially for those closed air-conditioned rooms, there should be certain humidity control equipment. 2, laying anti-static floor, control room and operation room are required to lay anti-static floor. 3. When maintaining the card or holding it by hand, you must first pay attention to the electrostatic discharge of your opponent and try to avoid direct contact with the electronic components, panel circuits and solder joints of the card. 4. Cards should be stored in antistatic plastic containers or antistatic plastic bags, and stored in card boxes. 5, system maintenance should also pay attention to wear DCS anti-static wrist.

Question What data should be backed up during the daily maintenance of DCS? Answer: It is necessary to back up data that are considered important, such as configuration, PID parameters, process parameters (set values), system installation software, computer drivers, trends and reports. Q9: How to quickly eliminate the display fault of a measuring point signal (temperature, pressure or flow rate, etc.). ) in DCS system?

Answer: Incorrect or non-display of signal display data is a common problem, which may be caused by field instruments or DCS. The methods of quick judgment are: 1, simulating standard signal test with signal generator (provided that there must be available signal generator on site), or connecting another signal cable of the same type to this channel for signal introduction test. If it is normal, check whether the DCS signal input on site is wrong. 2. Check whether the positive and negative signal wires are connected reversely, whether the jumper of the card is set correctly (especially the new point), and whether the parameters such as configuration model, range and compensation are set incorrectly. 3. Check whether other measuring points of the card to which the signal belongs work normally, and judge whether it is a card fault by replacing the spare parts of the card according to the actual situation on site, and pay attention to the jumper setting when replacing. Q 10: sometimes the monitoring of the operating station will automatically quit. Is it abnormal? A: There are many reasons for the system to quit. It is normal for the system to occasionally exit 1 times in a few months, because if the computer occupies too much memory or runs too many programs, it may affect the monitoring exit. But if you quit frequently (such as daily or weekly), this is not normal. There are several reasons for the general system to quit: 1, the system software installation is not standardized, and it can be solved after reinstallation. 2. Multiple alarms occur at the same time, resulting in insufficient computer system resources to report errors. 3. The configuration path of the system call is the network path, not the local path. 4. Hardware failure such as motherboard or hard disk. 5. If the hard disk space is insufficient, you can automatically quit. Q 1 1: Abnormal after computer restart? A: The user uses Dell LCD monitor on site, and the operating system is WIN NT. After the operating system restarts, I can't enter the desktop normally, prompting that vga format is not supported. Communicate with maintenance personnel what they did before restarting the computer, and feedback will improve the resolution of the display. In the process of self-checking after improving the resolution, it can be judged that NT system can't recognize the display system. Enter the BIOS, and the system will return to normal after the default settings are restored. Q 12: Why does the operator's keyboard crash? A: Cause analysis: The keyboard shell is poorly grounded, and the impact of human static electricity on the keyboard will also cause the keyboard to crash. Solution: 1 When producing a new keyboard shell, the outsourcing unit is required to leave grounding holes or electrodes on the keyboard; 2. When installing, make the keyboard shell and keyboard cable reliably connected in a shielded way; 3. Remove part of the coating on the keyboard shell to make the shell have an effective grounding point. Q 13: What is the reason for the abnormal pressure signal? Answer: The pressure signal is full range, which is inconsistent with the actual situation. Disconnect the positive pole of the signal line behind the card, and the signal will change from full scale to about 8kg pressure signal (the range is 0- 13kg). Through field observation, the measuring point passes through the safety guardrail. Short-circuit the signal line, but after passing through the safety barrier, the signal shows normal. The preliminary judgment is that there is something wrong with the safety guardrail. The reason may be that the same set of signals, the safety barrier is grounded. When the safety barrier fails, another mA signal is coupled to the signal, resulting in signal interference. Q 14: how to check the thermal resistance signal? A: First, check the configuration of the thermistor to confirm that the model of the thermistor in the configuration is consistent with the actual model; Secondly, ensure that the upper and lower computer configurations are consistent. Finally, if you still suspect that there is something wrong with the temperature measurement, you can measure the resistance between the field thermal resistors A and B as r1; The resistance between b and c is R2. According to the temperature measurement principle of three-wire thermal resistor, the actual resistance value of thermal resistor can be obtained as R 1-2R2. Then look up the table to find out the corresponding temperature. This temperature is then compared with the monitored temperature. If there is a big difference, please replace the card and try again. Q 15: How to quickly troubleshoot system communication? Answer: If communication failure is found during system operation, the following checks should be made: 1. It is very important to know the specific failure phenomenon, whether it is total communication interruption, partial data communication abnormality or communication abnormality of an operating station. 2. Engineers can visit the monitoring fault diagnosis screen to observe whether there are any communication cards or bus fault alarms (such as data forwarding cards and main cards). If the card is found to be faulty, please replace it with spare parts. 3. Check whether the current network is unblocked and whether the power supply of switches and control stations is normal. The computer ping command can be used to check whether each network node is unobstructed. 4. Faults such as network cables, switches and SBUS wires may lead to network faults, so they can be eliminated and replaced for testing. 5. Check whether the IP settings of the problematic operating station are correct, whether the card addresses (main card and data forwarding card) are set correctly, whether the network card driver is installed correctly, and whether the network cable connection is incorrect (cross, etc.). ).？