Injection plastic PLC control system Anti -Granulator Machine

Date:2022-7-19 Author:Sam

1. Overview \u0026 nbsp;

\u0026 nbsp; \u0026 nbsp; The current application of PLC in injection molding machine control is becoming wider and wider. The reliability of the PLC control system directly affects the safety production and economic operation of the injection molding machine. The anti -interference ability of the system is the key to the reliable operation of the entire system. The various types of PLC used in the automation system are installed in the control room concentrated, and some are installed on the production site and each motor equipment. Most of them are in the harsh electromagnetic environment formed by strong electromagnetic circuits and strong electric equipment. In order to improve the reliability of the PLC control system, on the one hand, PLC manufacturers are required to use the ability to improve the equipment; on the other hand, it is required to pay great attention in engineering design, installation construction and maintenance. The anti -interference performance of the system. \u0026 nbsp;

2. Electromagnetic interference sources and the interference of the system \u0026 nbsp;

1. Generally affecting the interference sources of industrial control equipment, most of them occur in parts where current or voltage changes are changing. The strenuous parts of these charges are noise sources, that is, the source of interference. \u0026 nbsp;

The interference type is usually divided according to the causes of interference, noise
spinning machine
interference mode and noise’s waveform properties. Among them: different causes of noise, divided into discharge noise, surge noise, high -frequency oscillation noise, etc.; According to the waveforms and properties of noise, it is divided into continuous noise, occasional noise, etc Molester interference and differential interference. Common model interference and differential model interference are more commonly used classification methods. Co -mode interference is the potential difference between the signal to the ground, which is mainly formed by the communist state (same direction) of the power grid, the difference between the land power difference and the space electromagnetic radiation on the signal line. The co -mode voltage is sometimes large, especially the power supply room with poor isolation performance. The co -mode voltage of the transmitter output signal is generally high, and some can reach up to 130V. The co -mode voltage can be converted into a differential voltage through the asymmetric circuit, which directly affects the measurement and control signal, causing damage to components (this is the main cause of the high damage rate of some system I/O modulus). It can also be for communication. Differential mold interference refers to the interference voltage that acts between the signal two poles. It is mainly used by the space electromagnetic field coupling induction between the signal and the voltage formed by the unbalanced circuit interference. control precision. \u0026 nbsp; 2. The main source of electromagnetic interference in the PLC control system \u0026 nbsp;

(1) radiation interference from space \u0026 nbsp;

The radiation electromagnetic field (EMI ) It is mainly by the temporary process of electric network and electrical equipment, Lightning, radio radio, television, radar, high -frequency induction heating equipment, etc., are usually called radiation interference, and its distribution is extremely complicated. If the PLC system is placed in the frequency field where the radiation is placed, the influence is mainly through the two paths: First, the radiation inside the PLC is directly interfered by the circuit induction; The induction of the communication line introduces interference. Radiation interference is protected by the size of the electromagnetic fields generated by the on -site equipment and the electromagnetic fields generated by the equipment, especially the frequency. Generally, it is protected by setting up the shielding cable and PLC local shielding and high -voltage leakage components. \u0026 nbsp;

(2) Interference from the out -of -the -system lead \u0026 nbsp;

is mainly introduced through the power supply and signal line, which is usually called conduction interference. This interference is more serious at the industrial site in my country. \u0026 nbsp;

The interference from the power supply \u0026 nbsp; \u0026 nbsp;
Practice has proved that there are many cases of the PLC control system failure due to the interference of the power supply. The higher PLC power supply is solved. \u0026 nbsp;

The normal power supply of the PLC system is powered by the power grid. Due to the wide range of grid coverage, it will be induced by all space electromagnetic interference and the induction voltage and circuit on the line. Especially the changes inside the grid, the switching operation waves, the start and stopping of large power equipment, the harmonics caused by the passing drive device, and the short -circuit of the power grid, etc., all pass to the original side of the power supply through the transmission line. The PLC power supply usually uses isolation power, but its institutions and manufacturing process factors make it unsatisfactory. In fact, due to the existence of distributed parameters, especially distributed capacitors, absolutely isolation is impossible. \u0026 nbsp;

The interference \u0026 nbsp; \u0026 nbsp;
Various signal transmission cables connected to the PLC control system from the signal line. In addition to the various types of information transmission, there will always be external interference signals invading. There are two main channels for this interference: first, the power grid interference in the power supply power supply of the power supply or the shared signal instrument through the transmitter, which is often ignored; the second is the interference of the signal line by the space electromagnetic radiation sensing, that is, the signal line on the signal line The external sensing interference is very serious. Signal introduction interference will cause abnormal I/O signal work abnormalities and measurement accuracy, and will cause component damage in severe cases. For systems with poor isolation performance, it will also cause interference between signals, causing the backflow of the common ground system, causing logical data changes, errors and crashes. The PLC control system is very serious due to signal introduction interference, which causes many cases of system failure. \u0026 nbsp;

Interference from when the grounding system is chaotic. \u0026 nbsp; \u0026 nbsp;
Grounding is one of the effective means to improve electronic equipment electromagnetic compatibility (EMC). Correct grounding can inhibit the effects of electromagnetic interference, but alsoIt can inhibit the device out of interference; and the wrong grounding will introduce serious interference signals, making the PLC system unable to work properly. \u0026 nbsp;

The ground lines of the PLC control system include systematic land, shielded land, communication ground, and protective land. The disorder of the grounding system chaos on the PLC system is mainly due to uneven distribution of the potential of each ground place. There are differences in ground potential differences between different ground locations, causing the current circuit current and affecting the normal operation of the system. For example, the cable shielding layer must be grounded a little. If both ends of the cable shielding layer are grounded, there is a difference in ground potential, and the current flows over the shielding layer. When an abnormal state such as lightning strikes, the ground line current will be larger. \u0026 nbsp;

In addition, the shielding layer, ground line, and earth may constitute a closed loop. Under the action of changing magnetic fields, there will be inductive currents in the shielding layer. Through the coupling between the shielding layer and the core wire , Drive the signal loop. If the system is chaotic with other grounding treatment, the generated ground flow may generate the potential distribution on the ground line, which will affect the normal operation of logic circuits and simulation circuits in the PLC. The logical voltage interference of PLC work is low, and the distribution interference of the logical potential potential can easily affect the logical operation and data storage of PLC, causing data confusion, program running or crash. The distribution of simulated ground potential will lead to a decrease in measurement accuracy, causing serious distortion and misunderstanding of signal measurement and control. \u0026 nbsp;

(3) interference from the internal \u0026 nbsp;

is mainly generated by the mutual electromagnetic radiation between the internal components and circuits of the system, such as the logical circuit radiating and its analog circuit The influence of simulation and logical land and the use of components are not matched with each other. This belongs to the content of the PLC manufacturer’s electromagnetic compatibility inside the system. It is more complicated. It cannot be changed as the application department. It does not need to consider too much, but choose a system with more application performance or test. \u0026 nbsp;

3. The anti -interference design of the project application of the PLC control system. Three aspects of inhibitory measures: suppress the source of interference; the transmission pathway of cutting or attenuation of electromagnetic interference; improve the anti -interference ability of the device and system. These three points are the basic principles of inhibiting electromagnetic interference. \u0026 nbsp;

The anti -interference of the PLC control system is a system engineering that requires manufacturing units to design and produce products with strong anti -interference capabilities, and depends on the use of the department in engineering design, installation construction, operation and maintenance Comprehensive consideration and comprehensive design in combination with the situation can ensure the electromagnetic compatibility and operating reliability of the system. When the anti -interference design of specific engineering is carried out, the following two aspects should be mainly. \u0026 nbsp;

1. Device selection \u0026 nbsp;

When choosing a device, we must first choose a product with high anti -interference capabilities, including electromagnetic compatibility (EMC), especially anti -external interference capabilities, such as PLC systems with floating ground technology and good isolation performance; second The anti -interference indicators given by the manufacturer, such as a total of simulation system, differential modeling ratio, pressure resistance, allowing how much electric field strength and high -frequency magnetic field strength environment; Application performance. \u0026 nbsp; When choosing foreign imports, it should be noted that my country uses 220V high internal resistance grid, while Europe and the United States are 110V low internal resistance grids. Due to the large internal resistance of my country’s power grid, the drifting of the zero point of the zero point, and the large changes in the land potential, the electromagnetic interference of the industrial enterprise on -site is at least 4 times higher than that of Europe and the United States. The anti -interference performance of the system is higher. In domestic industries, it is not necessary to run reliable. This must be reasonably selected according to my country’s standards (GB/T13926) when using foreign products. \u0026 nbsp;

2. Comprehensive anti -interference design \u0026 nbsp;

mainly considers several types of inhibitory measures from outside the system. The main contents include: blocking the PLC system and external leadership to prevent the air -to -space radiation electromagnetic interference; isolation and filtering the external lead, especially the principle power cable, layered layered to prevent the transmission electromagnetic interference through the external lead; correctly design the grounding site And ground device to improve the grounding system. In addition, software must be used to further improve the security and reliability of the system. \u0026 nbsp;

4. Main anti -interference measures \u0026 nbsp;

1. Use good power supply to inhibit the interference \u0026 nbsp;

in the PLC control system, the power supply system, the power supply Posted a very important position. The power grid interference string into the PLC control system is mainly entered through the power supply of the PLC system (such as CPU \u0026 NBSP; power supply, I/O power supply, etc.), the power supply power supply of the transmitter and the power supply power supply with direct electrical connection with the PLC system. At present, the power supply of power supply for the PLC system generally uses a good power supply, and the power supply of the instrument supply of direct electrical connection for the power supply of the transmitter and the PLC system is not received enough. The isolation measures are generally not enough. It is mainly used by the distribution parameters of the isolation transformer, the poor inhibitory interference ability, and the co -mode interference and differential mode interference through the power coupling. Therefore, the distribution capacitor and large inhibitory belt (such as multiple isolation and shielding and leakage technologies) should be selected for transmitter and common signal instrument power supply to reduce the interference of the PLC system. \u0026 nbsp;

In addition, it is necessary to ensure that the feeding point of the grid is not interrupted, and an online uninterrupted power supply (UPS) can be used to improve the safety and reliability of power supply. And UPS also has strong interference isolation performance, which is an ideal power supply for the PLC control system.\u0026 nbsp;

2. Ao set in the cable \u0026 nbsp;

In order to reduce the power cable radiation electromagnetic interference, especially the frequency conversion device feeds the electric cable. In a certain project, the author uses a copper -belt armor to shield the power cable, which reduces the electromagnetic interference of the power line production. The project has achieved satisfactory results after being put into production. \u0026 nbsp;

Different types of signals are transmitted by different cables, respectively. The signal cable should be layered in layers according to the type of transmission signal. It is strictly forbidden to use different wires of the same cable Close to parallel Ao to reduce electromagnetic interference. \u0026 nbsp;

3. Hardware filtering and software anti -interference measures \u0026 nbsp;

Signal before accessing the computer, and connect capacitors between the signal line and the interface to reduce co -mode interference; in the signal; Polarized filters between poles can reduce differential module interference. \u0026 nbsp;

Due to the complexity of electromagnetic interference, it is impossible to eliminate the impact of greeting interference. Therefore, in the software design and configuration of the PLC control system Improve the reliability of the system. Some common measures: digital filtering and industrial frequency plastic surgery, which can effectively eliminate cyclical interference; regular correction reference point potential, and use dynamic zero points to effectively prevent potential drift; use information redundancy technology, design corresponding software flags; Adopting indirect jump, setting up software traps, etc. to improve the reliability of the software structure. \u0026 nbsp;

4. Select the ground point correctly to improve the grounding system \u0026 nbsp;

The purpose of grounding is usually two, one is for safety, and the other is to suppress interference. The perfect grounding system is one of the important measures for the anti -electromagnetic interference of the PLC control system. \u0026 nbsp;

The system grounding method is: floating ground, direct grounding, and capacitor grounding. For the PLC control system, it is a high -speed and low -level control device, which should be directly grounded. Due to the effects of signal cable distributed capacitors and input device filtering, the frequency of signal exchange between devices is generally lower than 1MHz, so the PLC control system ground wire uses a little grounding and tandem. The concentratedly arranged PLC system is suitable for a parallel grounding method. The center of the cabinet center of each device leads to the grounding pole with a separate ground line. If the device is large, a series of grounding should be used in series. Use a large cross -section copper bus (or insulating cable) to connect the center of the cabinet in each device, and then directly connect the ground -to -ground line. The ground wire uses a copper guide line with an cross -section of 22mm2, and the total bus is a copper volleyball with an cross section greater than 60mm2. The grounding resistance of the ground pole is less than 2Ω. It is best to be buried in the building 10 \u0026 nbsp; ~ \u0026 nbsp; 15m far away, and the PLC system places must be more than 10m apart from the strong power equipment.Essence\u0026 nbsp;

When the signal source is connected, the shielding layer should be on the signal connection; when not ground, it should be grounded on the PLC side; when there is a connector in the middle of the signal line, the shielding layer should be firmly connected and performed.Avoid multi -point grounding; when the shielding of the twisted pair of multiple measuring points signals is connected to the multi -core pair -to -twisted screen cable, each shielding layer should be connected to each other and pass through insulation.Select the appropriate single -point connection at the ground.\u0026 nbsp;

5. End language \u0026 nbsp;

The interference in the PLC control system is a very complicated problem. Therefore, in the design of anti -interference designAnti -interference, you need to do specific analysis for some interference, and adopt the method of taking the right medicine to make the PLC control system work normally