Application of PLC in belt transformation

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1 Introduction The zinc nitrate belt is one of the important equipment for zinc nitrate production. However, the zinc nitrate production site has a lot of dust and corrosion, and the distance between the control room and the on-site control components is far, and there are many series loop control components. The belt often breaks down frequently due to high contact resistance or poor contact, and often stops or fails to start, which brings great difficulties to production and maintenance. In the past, many modifications were made to reduce contact resistance and voltage drop, but the results were very small. The reason is that the line between the field cable and the contactor coil is as long as 500m, and the use of traditional contactor control cannot reduce the length of the control line and control components. Figure l shows one of the contactor control circuits of the belt. In the figure, QC is the universal selector switch, 1SOFF and 1SFW are on-site start and stop buttons, 1HH-3HH are emergency stop buttons, 1K is the thermal element, and KA is the contactor coil. At the same time, there are also unsafe factors in the transportation of zinc nitrate belts. For the sake of safety, the bell must be rung before starting, and the bell must be rung at least 3 times, with an interval of several seconds, so that there is enough time to take measures to avoid danger before starting. However, in the past, the manual ringing method was used. Due to errors in each person's operation, the intervals may be longer or shorter. Some even forget the number of ringings and often ring more or less. The operation is cumbersome and unsafe. In view of the above existing problems, based on the viewpoint of simplicity, automation and safety first, PC automatic control is used to achieve the above requirements. 2 Theoretical analysis of the cause of the original contactor control failure In Figure 1, there are up to 7 components connected in series between Lines 1 and 2. The contact resistance of the series components is oxidized, causing the contact resistance to be too large. In addition to the power supply fluctuation factor, when the power supply between the contactor coils U≤70%, the contactor cannot pull in. When the power supply between the contactor coils U≤30%, the coil will return. http://www.nmtech.com.cn/jishuwang/upload/070124837345185.jpg Solution: Reduce or eliminate the number of circuit components, reduce the contact resistance between the coil and the power supply, shorten the cable length, stabilize the power supply voltage, etc. These methods can only limit the impact of contact resistance on the relay. 3 Reasons for using new programmer control The programmer control is very little affected by the power supply. The input side power supply is DC24＼AC110V, and the working power supply is a wide power supply AC110~240V. At the same time, programmer control is used to completely isolate the contactor from the field control components. The distance from the programmer to the contactor is only 1m. The maximum contact resistance of the field control components will not exceed 4Ω. The contact resistance * * decrease. The programmer controls the bell ringing with high accuracy in time and number of times. Reduces errors and errors caused by human operation. Also use a programmer * * The number of relays is reduced (12 if relay control is used). Programmer control reduces the number of serial components in the loop, and the series loop eliminates the transfer switch QC and thermal components, making the loop more reliable. * * improve. Programmer control reduces the number of cables to the field and makes contactor wiring simpler. 4 New programmer control schematic diagram Figure 2 is a programmable programmer control diagram, which is designed as a control schematic diagram for 4 belts. Both the thermal element and the emergency stop switch use normally open contacts, which is fundamentally different from the previous control method. On the one hand, the normally open connection can prevent the disadvantages caused by the use of normally closed contacts in field switches (contact release due to mechanical vibration). The thermal element is used as both an alarm and a parking element. The belt opening and parking button is an on-site explosion-proof button, and the emergency stop switch is an airtight selector switch. Each belt emergency stop switch is connected in series. In the figure, only one is drawn to simplify the circuit. The emergency stop is a parallel connection for each belt button. The wiring is simple and reliable, both in terms of the number of components and the number of terminals. * * are reduced, making installation and troubleshooting easier. http://www.nmtech.com.cn/jishuwang/upload/070124838339777.jpg http://www.nmtech.com.cn/jishuwang/upload/070124840002616.jpg http://www.nmtech.com.cn/jishuwang/upload/070124840542767.jpg5 Before starting the logic diagram of the programmer, first press the bell button 0001, 0507 starts, and the bell starts. After T10 passes for 5 seconds, the bell stops. At the same time, M0001 works. After T11 passes for 3 seconds, close 0507, and the bell starts again. After 3 times, CNT disconnects and rings the bell 0507, 0509 allows the driving light to turn on. After another 5 seconds, if 0002 is not closed, the belt cannot drive. On the contrary, within 5 seconds after the driving permission light turns on, if 0002 closes, the drive is successful. Ring the bell intermittently several times to give on-site operations or maintenance personnel enough reaction time to leave the belt and prevent accidents. If the operator does not press the start button within the specified time after ringing the bell, it means that the on-site belt processing or other reasons cannot meet the driving conditions, then the ringing of the bell will be invalid, the driving lights are allowed to go out, and the bell will be ringed again next time. When driving, if the selection position of the on-site selector switch is in the interlocking position, 0003 is closed, and the driving is started under the premise that the emergency stop switch and the thermal element are not activated. In order to meet the process requirements during startup, according to the principle of sequential startup, the fourth skin is started first, after the fourth skin is started, there is a delay of 2 seconds, the third skin is started, and so on, gradually starting the three skins to the first skin. If the selector switch is turned to single unit (0003 normally open), the single unit will start and the interlock will be released. In case of failure, 0508 fault alarm occurs, protection takes action, and all belt circuits are disconnected.