Common faults and handling methods of the hottest

Common faults and handling methods of PLC

Maintenance overview

generally, all types of PLC (the SR series PLC produced by Wuxi Huaguang Electronic Industry Co., Ltd. is used as the description template below, and the other types of PLC are similar) are designed to work continuously in the long term. However, it is also necessary to modify actions in some places occasionally. It is very important to quickly find this place and modify them. It takes a lot of time to modify actions that occur outside the PLC

fault finding equipment

sr PLC indicator light and internal equipment are beneficial to the fault finding of the whole PLC control system. The programmer is the main diagnostic tool, which can be easily plugged into the PLC. The state of the whole control system can be observed on the programmer. When you go to find the fault of the control system with PLC as the core, as a habit, you should bring a programmer

basic fault finding sequence

raise the following questions and deny them one by one according to the reasonable actions found. Replace various modules in SR step by step until all faults are eliminated. All major corrective actions can be completed by replacing the module. Except for a screwdriver and a multimeter, there is no need for special tools, oscilloscopes, advanced precision voltmeters or special test procedures

1. Is PWR light on? If it is not on, check the power supply voltage at the voltage input terminal (VAC or VAC) of the frame with AC power supply; For frames that require DC voltage, measure the DC voltage between the +24vdc and 0vdc terminals. If it is not a suitable AC or DC power supply, the problem occurs outside the SR PLC. If the AC or DC power supply voltage is normal, but the PWR light is not on, check the fuse and replace the CPU frame if necessary

2. Is PWR light on? If it is on, check the error code displayed, and make corresponding corrections against the code definition in the error code table

3. Is the run light on? If not, check whether the programmer is in the PRG or load position, or whether there is a program error. If the run light is not on and the programmer is not plugged in, or the programmer is in run mode and does not display an error code, the CPU module needs to be replaced

4. Is the batt light on? If it is on, the lithium battery needs to be replaced. Since batt light is only an alarm signal, even if the battery voltage is too low, the program may not have changed. After replacing the battery, check the program or let the PLC test run. If the program has errors, reload the program recorded on the tape into the PLC after completing the initialization of system programming

5. In a multi frame system, if the CPU is working, the run 'relay can be used to check the operation of several other power supplies. If the run relay is not closed (high resistance state), check the AC or DC power supply according to the first step mentioned above. If the AC or DC power supply is normal and the relay is disconnected, the frame needs to be replaced

general troubleshooting steps

other steps are related to the user's logical knowledge. In fact, the following steps are only relatively common, and they need to be modified or adjusted for the specific application problems you encounter. The best tool to find faults is your feeling and experience. First, plug in the programmer and turn the switch to the run position, and then follow the following steps

1. If the PLC stops at the place where some outputs are excited, and it is generally in the intermediate state, look for the signal that causes the next operation (input, timer, line stream, drum controller, etc.). The programmer will display the on/off state of that signal

2. If the input signal, compare the status displayed by the programmer with the LED indication of the input module, and the result is inconsistent, replace the input module. At present, there are multiple modules to be replaced on the expansion frame, so before you replace the module, you should first check the i/o and adjust the hardness tester to the level; (2) The connection between the expansion cable and the steel ball whose surface is not smooth or whose diameter exceeds the tolerance

3. If the input state is consistent with the LED indication of the input module, it is necessary to compare the state of the LED and the input device (button, limit switch, etc.). The two are different. Measure the input module. If there is a problem, replace the i/o device, field wiring or power supply; Otherwise, replace the input module

5. If the signal is a line stream and there is no output or the state of the output is different from that of the line stream, you have to use a programmer to check the drive logic of the output and check the program list. The inspection should be carried out from there to left. Find out the first contact that is not connected. If the one that is not connected is the input, press the second and third steps to check the input point. If it is a line, press the fourth and fifth steps to check. Make sure that the main control relay step affects the logic operation

6. If the signal is a timer and stops at a non-zero value less than 999.9, replace the CPU module

7. If this signal controls a counter, first check the logic of control reset, and then the counter signal. Proceed according to 2 to 5 above

replacement of components

the following are the steps to replace the sr-211pc system

first, replace the frame

1, cut off the AC power supply; If a programmer is installed, unplug the programmer

2. Unplug the plastic cover plate from the terminal board at the right end of the frame and remove the power wiring

3. Unplug all i/o modules. If there are multiple working circuits during the original installation, don't mess up the wiring of iu/o, and write down the position of each module in the frame, so as not to make mistakes when re plugging

4. If the CPU frame, unplug the CPU components and fill the module. Put it in a safe place for reinstallation later

5. Remove the two screws fixing the frame at the bottom and loosen the two screws at the top, but do not remove them

6. Push the frame up, and then pull it down and put it next to it

7. Insert the new frame from the top screw,

8. Install the bottom screw and tighten the four screws

9. Insert the i/o module, and pay attention to the same position as when it is removed

if the module is inserted in the wrong position, it will cause dangerous or wrong operation of the control system, but will not damage the module

10. Insert the removed CPU and filling module

11. Reconnect the power wiring on the terminal on the right side of the frame, and then cover the plastic cover of the power terminal

12. Check whether the power connection is correct, and then turn on the power. Carefully check the operation of the whole control system to ensure that all i/o modules are in the correct position and the program has not changed

II. Replacement of CPU module

1. Cut off the power supply and unplug the programmer if it is plugged in

2. Squeeze the upper and lower fastening buckles of the CPU module panel in the middle to make them out of the bayonet

3. Pull the mold out of the groove vertically

4. If EPROM memory is installed on the CPU, unplug the EPROM and install it on the new CPU

5. First align the printed circuit board with the bottom guide slot. Insert the new CPU module into the bottom guide

6. Slightly shake the CPU module to align it with the top guide slot

7. Insert the CPU module into the frame until the two elastic latches buckle into the bayonet

8. Plug in the programmer again and power on

9. After the system is programmed and initialized, reload the program recorded on the tape. Check the operation of the whole system. These measures include reducing the package size

III. replacement of i/o module

1. Cut off the power supply of the frame and i/o system

2. Remove the plastic cover on the terminal of the i/o module. Remove the field wiring of the faulty module

3. Remove the field wiring of the i/o terminal or the removable wiring socket, depending on the type of module. Label each wire or mark the installation wire for future reconnection

4. Squeeze the upper and lower elastic latches of the i/o module in the middle to make them out of the bayonet

5. Pull out the i/o module vertically

common fault analysis and maintenance of PLC process control

in order to prolong the service life of PLC control system, it is necessary to have a clear estimate of the equipment consumption and component equipment failure point of the system in the system design, production and use, that is to say, it is necessary to know which parts of the whole system are most prone to failure, so as to take measures. This paper will analyze the fault distribution law of PLC process control system

in order to prolong the service life of the PLC control system, it is necessary to have a clear estimate of the equipment consumption of the system and the failure point of components and equipment in the system design, production and use, that is to say, it is necessary to know which parts of the whole system are most prone to failure, so as to take measures. Taking the PLC process control system of special cement line 1 of our plant as an example, this paper analyzes the fault distribution law of the PLC process control system, hoping to be helpful to the system design and maintenance of the PLC process control system

1. The concept of system failure

system failure generally refers to the total failure of the entire production control system, which can be divided into PLC failure and field production control equipment failure. PLC system includes central processing unit, mainframe, expansion chassis, I/O module and related network and external equipment. The on-site production control equipment includes I/O ports and on-site control and detection equipment. What are the methods to maintain the tension machine, such as relays, contactors, valves, motors, etc

2. Fault statistics, analysis and treatment of the system

2.1 introduction to the process control system of special cement line 1 of our plant

during the transformation of the system in 2000, the PLC process control system with A2 series pic of Mitsubishi Corporation of Japan as the core was adopted

the system has two centralized control rooms: kiln tail control room and kiln head control room, of which the kiln head control room is the main station; Two on-site workstations: automatic raw material batching workstation at the kiln end and automatic water adding and pelletizing workstation at the kiln end; Two TV monitoring systems: preheater inlet blanking monitoring and kiln head TV fire watching. The on-site workstation is an independent microcomputer automatic control system, which only communicates with the master station with analog quantities and interlocks with switching quantities. Frame synchronous full duplex communication mode is adopted between master station and slave station:

2.2 system

statistics of fault data

statistics of PLC faults in the past three years of operation of the system are shown in Table 1

the fault statistics of field control equipment are shown in Table 2

according to the statistics, the total number of system faults is 126, of which the fault proportion of PLC is about 4.7%, and the fault proportion of field part is about 95.3%. Compared with the fault data of other PLC process control systems, and considering that the operation time of the system is not very long, this proportion is relatively close to the fault distribution law of general PLC process control systems, and has a certain universality. Generally speaking, the failure rate of PIC part is about 5%, and the failure rate of field control equipment is about 95%

estimation of fault distribution of PLC process control system

2.3 system fault analysis and treatment

2.3.1 PLC host system

plc host system is most prone to failure in the power supply system and communication network system. In the continuous work and heat dissipation of the power supply, the fluctuation impact of voltage and current is inevitable. Communication and network are likely to be interfered by external factors, and the external environment is one of the biggest factors causing the failure of external communication equipment. The damage of the system bus is mainly due to the fact that most PLCs are plug-in structures. The long-term use of plug-in modules will cause damage to the bus at local printed boards or backplanes, connector interfaces, etc. under the influence of changes in air temperature and humidity, the plastic of the bus is aging, and the printed circuit is aging