Fault analysis and treatment of automatic shutdown

Analysis and treatment of s5plc automatic shutdown fault

s5 series PLC is the leading industrial process control model of Siemens in Germany, which is widely used in metallurgical, chemical and other industrial production process control in China. Due to the poor production environment in the metallurgical industry and the influence of metal dust, some faults in the application are common, such as the sudden automatic shutdown of CPU in the work (commonly known as "crash"). Combined with the practical application of Siemens S5 series PLC in Laigang 3# continuous casting, lime shaft furnace, hot delivery roller table and 4# oxygen production, this paper comprehensively analyzes the fault phenomenon of automatic shutdown in the operation of Siemens S5 series PLC, and discusses the solutions

the main reasons for the automatic shutdown of S5 series PLC in operation are as follows:

1 PLC power supply part

(1) power supply fluctuation, S5-115U, S5-150U, s5-155u series PLC power modules produced by Siemens have DC 24V, AC 115/230v and other models. The allowable voltage fluctuation range AC220V is +20% - -15%; DC24V is +25% - -16%. With such a loose allowable range, users can even use it without various voltage stabilizing devices when the power supply has a large enough capacity. However, when the power capacity is limited and the equipment with large load is started, it will cause instantaneous or short-term low voltage, which will exceed the allowable voltage fluctuation range and cause "crash". In another case, the power template adopts DC24V, and the i/o modules of the machine adopt DC24V voltage, and the power template and i/o template share one DC power supply. When the power supply line is long, with the increase of the load carried by the output template, the power supply current of the line increases, causing the line voltage drop to exceed the allowable fluctuation range of PLC, which will also cause automatic shutdown. These two kinds of "dead" faults do serious harm to the PLC itself and the equipment it controls, especially when the power supply template and i/o template share the same power supply, the PLC starts up and runs, and the line voltage drop causes the shutdown. After the shutdown, the voltage rises, and then starts up and runs, and then stops. This repeatedly causes the PLC to start up with load, causing serious damage to the controlled equipment, and sometimes does not contain iron and other impurities that are easy to heat and turn yellow; Unnecessary major personal and equipment accidents will occur. In view of the above situation, if the power capacity is insufficient, the power supply capacity should be increased or voltage stabilizing equipment should be added. If the line voltage drop is large, the wire section or the power supply template and i/o template can be appropriately increased to supply power separately

(2) the power supply on the expansion board unit loses power, causing the QVI red light to light when the CPU is shut down. For this reason, you can find the power supply on the expansion unit and eliminate the failure of the power supply to improve the reliability of power supply

(3) the voltage of the 24V DC external power supply on as311 is too low, and its value is not between 20-30v, or the voltage fluctuation is too large, and the filtering is poor, which cannot ensure the normal operation of the CPU in the remote communication template im311. For this reason, in order to maintain the voltage value between 20-30v during the operation of the system, the AC voltage stabilizing device can be installed before 24VDC or the 24V ddz-Ⅲ 5A DC instrument power supply for the communication template can be used for separate power supply

2 in terms of software programming, S5 series PLC system software is rich, and the application software adopts program block structure. Users can compile several functional program blocks according to different controls, and then the block calls the program to complete all control tasks. Due to the different ideas and styles of programming, if you are careless, it will cause sudden automatic shutdown in the operation of PLC due to the programming of software, which is mainly manifested in the following aspects:

(at the same time, it continues the toughness, wear resistance, heat resistance of nylon 66 and the chemical corrosion resistance of the experimental data made in the future if there is a gap between the screw rods. 1) the cycle of program operation is greater than the cycle time set by the user. If you shut down for this reason, The "zyk" red light on the CPU should be on during shutdown. This situation can be solved by modifying the set time or modifying the software to reduce the cycle time

(2) if the "QVI" red light of the CPU is on during shutdown, it indicates that the information of some modules read in or output by the CPU takes longer than the time specified by the system. This fault condition is caused by the following reasons:

a. the template set on the discrete expansion board 306 is removed or some discrete expansion boards fail

b. replacement error, all data words in the program are undefined or the used function block parameters are filled in incorrectly

c. the power supply on the expansion board unit loses power, or the power supply part of the expansion board fails

the specific treatment method for the above various fault causes is: when a certain fault occurs, you can search the user address setting area on the programmer through F7 and F8 function keys, see whether the address recognized by the CPU is consistent with the address set by the user on the discrete expansion board im306, find out the cause and eliminate it. Most cases are caused by the unstable work of in306 template. For the second fault phenomenon, you can check the user interrupt stack, use F7, F8 or F7, F6 keys to find out which program block or data block is the error, and modify its software to solve it

(3) in the program with the ability to manage a full set of solutions for interrupting spray free materials, the same flag is used in the cycle program (i.e. the main program) and the interrupt service program (i.e. the subroutine). When returning from the interrupt service program, it is possible to change the status of the flag in the cycle program, resulting in errors or unnecessary downtime. The solution is to modify the software

(4) there is a logic error in the programming, which causes the program to enter the dead cycle and cannot exit; Or using illegal statements will also cause downtime and correct errors in programming

3 hardware configuration

(1) the control system composed of S5-150U and s5-155u models is selected in the production process control of metallurgical enterprises, which is prone to automatic shutdown. The reason is that these two models are bare trigger models, so the requirements for conductive dust are higher than those of S5-115U series. The PLC of s5-155u model is selected for our 3# continuous casting, and the automatic shutdown phenomenon is caused by the natural creepage caused by the conductive dust falling on the machine board. Therefore, when using s5-155u and S5-150U models, fully consider the requirements of the model on the working environment to reduce the impact of conductive dust on the normal operation of the machine. PLC cabinet positive pressure technology can also be used

(2) there are often occasional failures on the production site, and sometimes after shutdown, cold start can work; Sometimes it is necessary to retransmit the program (use the programmer to cover the copied program with the original PLC program) in order to be effective. In this case, it is generally a software problem. As long as necessary technical operations are carried out, the fault can be eliminated. Otherwise, it is a hardware problem, which can be analyzed from two aspects; First, due to the poor on-site environment and long-term operation, there is too much dust at the template slot