Application of Mitsubishi industrial control products in electrical complete sets of equipment - News - Global IC Trade Starts Here Free Join

Spot Remarks 2017+

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Mitsubishi industrial control products are widely used in various industrial and mining enterprises. Although the quality of the products themselves has been guaranteed, the situation of the industrial site is ever-changing and the law is unclear. After the complete set of equipment, the whole system is inevitably disturbed. Since interference is a process of interaction, the effect of either party on the other party can cause system failure. Therefore, it is very complicated in principle analysis and practical solution, both for situational judgment and practical experience. According to the current users, the source of the problem is more likely to occur in the process of using the product:

1 Due to the large equipment and scattered layout, the wiring is too long, the path is unreasonable, resulting in poor grounding, formation of interference loops, generation of line noise, and interaction with related equipment.

When the 2nd line is not in accordance with the principle of strong and weak electricity, the power, control and communication are combined. The power is easier to distinguish, and the control signal content is more, and its classification is different according to different actual requirements.

3 The interaction between related equipment and system, generally electromagnetic interference, roughly:

a) Equipment with pulse generation source such as inverter and servo device

b) Equipment for generating pulses and arcs, such as wire cutters and EDM machines

c) Jitter of the lighting device (fluorescent lamp) during the opening phase

d) Reverse peak voltage when the relay and contactor are released

e) peripheral equipment is close to part of the signal frequency of the system

The basic classification of a control signal:

1 switch (digital) type input

a) Dry contact --------- operation button (switch), stroke and limit switch, relay, contactor auxiliary contact, etc. Since the conduction current of the plc input terminal is 5-7 mA, in order to ensure signal stability, the current must be maintained at 3.5 and 4.5 mA when the input terminal is turned on. If it is bad due to poor contact or the wire is too long, it is susceptible to interference. In addition, larger contactor contact contacts should be considered for reliable contact at low currents.

b) Proximity switch, Photoelectric Switch, open collector type encoder, etc. --------- These components are mostly placed in the field, and there is a certain distance between the PLC and the PLC. A product with good switching performance. Generally, it is more susceptible to interference when the level interval/pulse width ratio is large.

c) Differential encoder--------- This type of sensor is more suitable for long-distance, high-speed applications, and the chance of interference is less than the former. The open collector type will attenuate the output level due to the long lead length.

2 switch (digital) output:

a) Relays ----------- used to drive contactors, solenoid valves, lights, electronic circuits and other equipment. The load power supply is below DC30V and below AC240V. In the case of AC loads, in order to facilitate the cable, such control signals can be placed together with the power line under normal conditions. The DC load is determined according to the voltage level and the nature of the equipment being driven.

b) Transistor output (DC5-30V) I drives relays, indicator lights, electronics, and other equipment. Interference factors should be considered for low voltage loads. II Drives the inverter, positioning device, electronic circuit, etc. in level or pulse form. It is recommended to keep at least 30cm in proper distance from the power line. Consider designing as far away as possible from equipment that may affect each other.

c) Precautions-----------Inductive components such as external load (contactor, solenoid valve) connected to PLC output should be connected with RC absorption circuit or freewheeling diode according to AC/DC property. Although the Mitsubishi plc promotion has not caused interference due to neglecting this work, it will shorten the life of its internal output components, and it will easily affect external electronic devices, and the effect is obvious.

3 analog input:

Connected to the PLC in the form of voltage or current, generally output from various types of detection or control equipment (sensors, instrumentation, etc.), such as they are susceptible to interference due to problems such as excessive line length, improper use or quality, and thus impede the system. Operation. Especially for small signals, current type input is recommended.

4 analog output:

It is output from the PLC to the relevant equipment in the form of voltage or current. Like the analog input, it pays attention to the reliability of small signals, such as interference and attenuation in long distances.

5 communication lines:

a) Optical cable ------------ Because of the way of level transmission, high-performance, low-loss information transmission can be performed. Can be immune to electromagnetic interference.

b) Coaxial cable and twisted pair----------- are all electrical connections, with level transmission characteristics. Due to the good medium and refined structure, the coaxial cable has a long distance, high speed, a large number of link stations and less interference, but the cost is high. The performance of the twisted pair in this respect is lower than that of the former, but the price is economical and the cable is convenient, and it can be made by itself. It is more suitable in the case of large system and limited space (requires terminal resistance). When arranging the communication cable, try to separate it from the power line and the control line and ensure that the communication of the whole system is smooth and undisturbed. At present, there is still little communication abnormality caused by Mitsubishi products due to interference.

Since the user selects Mitsubishi products as part of the system when the equipment is complete, it has configured a certain number of peripheral equipment, such as low-voltage electrical appliances, motors, solenoid valves, sensors, instrumentation, electronic circuits, computers, various networks and other industrial control products. . Some of these products or networks do not all have industry standards or have not been tested. System integration may have an impact on each other. Therefore, in the system design, component selection, equipment in place, installation, wiring, debugging, maintenance, etc., there are reasonable or not problems, there are congenital conditions and there are also human factors, or just after the normal operation, for many reasons Causes environmental changes and causes abnormalities.

In order to reduce the chance of interference in the complete set of electrical appliances, relevant preparatory work should be done in accordance with relevant industry regulations to eliminate hidden dangers. In view of the system design, equipment in place and other matters are subject to user's own production conditions, use requirements, funding conditions and other factors weighed, inconvenient to change, here only from the electrical aspects of the recommendations, including:

1 equipment in place ---------- In the case that the whole system has been determined (including the components in the electrical cabinet), refer to the principle, try to make the layout reasonable, and reduce the invalid cable path to reduce Harmful factors.

2 cable ------------ If the conditions are limited, the detailed classification should also be roughly divided into strong and weak electricity, and as far as possible to ensure that the cable reduces parallel opportunities to reduce the mutual inductance between the wires. In addition, when the weak signal line is long, the twisted pair can be used as needed to reduce the distributed capacitance and mutual inductance.

3 Even if the interference cannot be eliminated on the hardware, sometimes in some cases, the method of supplementing the corresponding program can be used to improve.

At present, according to users' reports, it is easy to cause interference when using high-speed counting, temperature control, inverter, servo (stepping) devices and other products.

1 high speed counting module AISD62:

The encoder is 30m away from the module, and there is a misalignment (pulse loss) when counting. Installation wiring requirements should be attached to the encoder and the power supply should be connected separately, but not through the module power line path, the situation is improved after correction.

2 thermocouple temperature module FX2N-4AD-TC:

The temperature value often jumps indefinitely, the range is 3-5 °C, which affects the work of the unit. The BFM of the average sampling points is repeatedly adjusted in the program, and there is no effect. After the shield end of the compensation wire is changed to 0V of the module power supply, the situation is obviously improved. The fluctuation range is 0.1-0.3 °C. In some cases, if the above measures are taken, it still has no effect. The thermocouple + transmitter + ordinary A/D module can be used. Since the transmitter itself has formed an isolation link, the numerical disturbance can be solved to a large extent. problem.

3 positioning module FX1S (1N), FX2N-1PG, FX2N-10 (20) GM:

The anti-interference measures for the positioning module and the servo can be found in the product manual. Here is a brief explanation of the connection to the stepper motor driver. Many stepper motor drivers are different from imported products. The common phenomenon is that the position error is large due to the motor out of step caused by the interference pulse. In addition to the similar method to the servo device, it is easier to install the filter. Improve it. Since the operating frequency range of the pulse-driven device is wide, it is difficult to calculate the input (output) impedance, so it is not easy to install components such as self-made filters. If improperly selected, it will not only absorb normal high-frequency pulses, but also reduce The level of response of the system, the application depends on the specific circumstances.

4 inverter FR-E500:

The user installed multiple A500 and E500 series inverters in the electric control cabinet. When running, there are multiple E500 inverters. The frequency on the operation panel is displayed as 0, and the RUN indicator is off, but it runs as usual. Press any key to resume display. During the observation, it was found that all the grounding ends of the inverter were connected to the cabinet of the electrical cabinet, and the cabinet was not grounded. Grounding is a more rigorous work, and it must be done thoroughly. If it is unconditional, it can be temporarily grounded. If it is half done and halfway, it will easily cause interference. The fault is eliminated after the equipment is delivered to the site and grounded.

5 inverter FR-A500:

When the inverter is running, it will interfere with the user control instrument. After the motor is removed, the inverter will run at no load. The system is normal. The initial judgment should be caused by the output line noise. Use the FR-BLF line noise filter to connect to the inverter U and V. Between the W end and the motor. The degree of interference is significantly reduced. If the line noise is not from the load but from the grid input, the filter can be connected to the R, S, and T terminals on the incoming side.

6 In some cases, because the interference cannot be completely eliminated, the program can be added in the software. The principle is to reduce the sensitivity of the interfered data, and to make it relatively slow and not easy to fluctuate through the timed average operation. Of course, it is only suitable for occasions where real-time requirements are not high.

The functions and technical data of the above products are only based on Mitsubishi products. The relevant content is just some of my experiences in the past work. These phenomena are far beyond the scope of a certain brand of products. In view of the complexity and uncertainty of the interference phenomenon and the field experience, some of the understandings are not comprehensive. It is hoped that the peers with relevant experience will supplement and correct, and better maintain and improve the credibility of the products they are engaged in.