附录
Abstract: Programmable controller in the field of industrial control applications, and PLC in the application process, to ensure normal operation should be noted that a series of questions, and give some reasonable suggestions.controller翻译中文
Key words: PLC Industrial Control Interference Wiring Ground Proposal Description
Over the years, programmable logic controller (hereinafter referred to as PLC) from its production to the present, to achieve a connection to the storage logical leap of logic; its function from weak to strong, to achieve a logic control to digital control of progress; its applications from small to large, simple controls to achieve a single device to qualified motion control, process control and distributed control across the various tasks. PLC today in dealing with analog, digital computing, human-machine interface and the network have been a substantial increase in the capacity to become the mainstream of the field of control of industrial control equipment, in all walks of life playing an increasingly important role.
ⅡPLC application areas
Currently, PLC has been widely used in domestic and foreign steel, petroleum, chemical, power, building
materials, machinery manufacturing, automobile, textile, transportation, environmental and cultural entertainment and other industries, the use of mainly divided into the following categories:
1. Binary logic control
Replace traditional relay circuit, logic control, sequential control, can be used to control a single device can also be used for multi-cluster control and automation lines. Such as injection molding machine, printing machine, stapler machine, lathe, grinding machines, packaging lines, plating lines and so on.
2. Industrial Process Control
In the industrial production process, there are some, such as temperature, pressure, flow, level and speed, the amount of continuous change (ie, analog), PLC using the appropriate A / D and D / A converter module, and a variety of control algorithm program to handle analog, complete closed-loop control. PID closed loop control system adjustment is generally used as a conditioning method was more. Process control in metallurgy, chemical industry, heat treatment, boiler control and so forth have a very wide range of applications
3. Motion Control
PLC can be used in a circular motion or linear motion control. Generally use a dedicated motion control module, for example a stepper motor or servo motor driven single-axis or multi-axis position control module, used in a variety of machinery, machine tools, robots, elevators and other occasions.
4. Data Processing
PLC with mathematics (including matrix operations, functions, operation, logic operation), data transfer, data conversion, sorting, look-up table, bit manipulation functions, you can complete the data collection, analysis and processing. Data
processing is generally used, such as paper making, metallurgy, food industry, some of the major control system
5. Communications and networking
PLC communication with the communication between PLC and the PLC and other communications between intelligent devices. Along with the development of factory automation network, the PLC now has communication interface, communication is very convenient.
ⅢApplication features of PLC
1. High reliability, strong anti-interference
High reliability is the key to performance of electrical control equipment. PLC as the use of modern large scale integrated circuit technology, using the strict production process, the internal circuits to the advanced anti-jamming technology, with high reliability. Constitute a control system using PLC, and the same size compared to relay contactor system, electrical wiring and switch contacts have been reduced to hundreds or even thousands of times, fault also greatly reduced. In addition, PLC hardware failure with self-detection, failure alarm timely information. In the application software, application are also incorporated into the peripheral device fault diagnosis procedure, the system is in addition to PLC circuits and devices other than the access protection fault diagnosis. In this way, the whole system extremely high reliability.
2. Fully furnished, fully functional, applicability
PLC to today, has formed a series products of various sizes, can be used for occasions of all sizes of industrial control. In addition to processing other than logic, PLC data, most of computing power has improved, can be used for a variety of digital control in the field. A wide variety of functional units in large numbers, so that penetration to the position of PLC control, temperature control, CNC and other i
ndustrial control. Enhanced communication capabilities with PLC and human-machine interface technology, using the PLC control system composed of a variety of very easily.
3. Easy to learn, well engineering and technical personnel welcome
PLC is facing the industrial and mining enterprises in the industrial equipment. It interfaces easily, programming language easily acceptable for engineering and technical personnel. Ladder language, graphic symbols and expressions and relay circuit very close to are not familiar with electronic circuits, computer principles and assembly language do not understand people who engage in industrial control to open the door.
4. System design, the workload is small, easy maintenance, easy to transform
PLC logic with memory logic instead of wiring, greatly reducing the control equipment external wiring, make the control system design and construction of the much shorter period, while routine maintenance is also easier up, even more important is to change the procedures of the same equipment has been changed production process possible. This is particularly suitable for many varieties, small batch production situations.
(1)Installation and wiring
●Power lines, control lines and power lines and PLC I / O lines should be split wiring, isolation transformer and PLC and I / O should be used between the cable connection Shuangjiao. The PLC's IO lines and power lines go separate lines, such as to be in the same groove, the separation of bundled communication lines, DC lines, if conditions allow, the best sub-groove alignment, not only will it have the greatest possible distance and can reduce the noise to a minimum.
●PLC should stay away from strong interference sources such as welding, high-power silicon rectifier devices and large power equipment, not with the high-voltage electrical switch installed in the same cabinet. PLC in the cabinet should stay away from power lines (the distance between the two should be more than 200mm). And PLC cabinets installed within the same inductive load, such as large power relay, contactor coil, arc should be parallel RC circuit.
●PLC input and output separately from the best alignment, switch and analog should be laid separately. The transmission of analog signals should be shielded cable, one end or both ends of the shield should be grounding resistance should be less than the shielding layer 1 / 10.
●AC output line and DC output lines do not use the same cable, the output line should be far from power lines and power lines, to avoid parallel.
(2)I / O wiring terminal
Input Connection
●Input wiring generally not too long. But if the environment interfere with small, small voltage drop, the input terminal can be properly longer.
●Input / output lines can not be used with a cable, input / output lines should be separated.
●The extent possible, normally open contact form to connect to the input in the establishment of the ladder and relay the same schematic, easy to read。
Output connection
●Output wiring is divided into separate output and public output. In different groups, using different types and voltage levels of output voltage. However, output in the same group can only use the same type, the same voltage level of power.
●As the PLC's output devices are packaged in printed circuit board and connected to the terminal board that if the load short-circuit connecting the output components, printed circuit boards will be burned.
●With relay output, inductive load borne by the size, will affect the relay service life, hence the use of inductive load shall exercise reasonable choice, or additions isolation relays.
●PLC may interfere with the output load, so to take measures to control, such as the DC output of the continued flow of control protection, exchange of the output RC snubber circuit, transistors and resistors Triac output bypass the protection.
ⅣPLC applications need to pay attention to the problems
PLC is an automation controls for industrial equipment, generally do not need to take measures, it can be directly used in industrial environments. However, despite the high reliability as mentioned above, strong anti-interference ability, but when the production environment is too harsh, especially strong electromagnetic interference,
or installed incorrectly, it may cause error or operator error, resulting in incorrect input and of the wrong output, this will result in loss of control and malfunction of equipment, which can not guarantee the normal operation of PLC, PLC control system to improve the reliability demands of its manufacturers improve equipment PLC's anti-jamming capability; the other hand, to design , installation and use of maintenance attach great importance to coordinate with to improve problem-solving, and effectively en
hance the system robustness. Therefore, in use should be aware of the following questions:
1 The work environment
(1)Temperature
PLC required temperature at 0 ~ 55oC, installation, heating large components can not be placed below the space around the ventilation and cooling should be large enough.
(2)Humidity
To ensure the PLC, insulation, air relative humidity should be less than 85% (no condensation).
(3)Shock
PLC should be made from a strong vibration source, to prevent the vibration frequency is 10 ~ 55Hz frequent or continuous vibrations. When the environment is inevitable when using vibration, shock absorption to take measures, such as glue, such as using shock absorption.
(4) Air
To avoid corrosion and flammable gases, such as hydrogen chloride, hydrogen sulfide, etc.. The more the air of dust or corrosive gas environment can be installed in
a closed PLC better control room or control cabinet.
(5) Power
PLC for the interference caused by power line has a certain ability to resist. The reliability of power supply in demanding or especially serious interference with the environment, you can install a isolation transformer with shielding to reduce interference between the equipment and land. PLC DC 24V output generally has provided input, when input when using an external DC power supply, DC power supply should be used. Because the average rectifier power supply, due to ripple effects, easy to PLC received an error message.
2. Control system interference and its source
On-site EMI PLC control system is the most common and most likely one of the factors affecting system reliability, the so-called root of the problem symptoms first, identify the problems and to propose solutions to the problem. Must be aware of on-site sources of interference.
(1)The source of interference and general classification
PLC control system affect the source of interference, most of current or voltage produced dramatic changes in the location, the reason is the current change in magnetic field, produces electromagnetic radiation on equipment; magnetic field change generated currents, electromagnetic waves generated high speed. Usually different modes of electromagnetic interference by interference, into common mode
and differential mode noise interference.
Common mode interference is the signal-to-ground potential difference, mainly by the network in series, to potential difference and the space of electromagnetic radiation in the common signal line sensor state (in the same direction) voltage superimposed formed. Common-mode voltage circuit can be converted by asymmetric differential mode voltage, direct impact on measurement and control signals, resulting in component damage (this is the number of system I / O module, the main reason for the higher failure rate), this can dc common-mode interference also for the exchange. Differential mode interference is the effect on the signal interference voltage between two poles, mainly by the electromagnetic field in the signal coupling induced by the unbalanced conversion circuit formed by the
common mode interference voltage, this disturbance superimposed on the signal directly affects the measurement and control accuracy.
(2) PLC system and the way the main source of interference
Strong electrical interference
PLC system, the normal power supply by the power supply. As the network scope, it will be all the space on a line of electromagnetic interference induced voltage. Internal changes, especially power, knife switching surges, large-scale power equipment starts and stops, caused by AC and DC drives harmonics, short circuit transient shocks are transmitted through the transmission line power of the original edge.
Cabinet interference
High-voltage electrical control cabinet, a large inductive load, confusing layout are easy on the PLC to a certain degree of interference.
The introduction of interference from the signal line
PLC control system is connected with all kinds of signal transmission lines, in addition to the effective transmission range of information but there will always be external interference signal intrusion. This interference There are two main ways: first, shared by the transmitter power supply or signal instrumentation string into the grid power supply interference, which are often neglected; second signal induced by the interference of electromagnetic radiation of space, that is the signal Online external sensor interference, this is very serious. Introduced by the signal interference may cause I / O signal abnormalities and accuracy of work significantly reduced, will cause severe damage components.
From the grounding system disorder, disturbance
Ground is to improve the electromagnetic compatibility of electronic equipment (EMC) is one effective means. Properly grounded, can not only inhibit the impact of electromagnetic interference, but also outgoing interference suppression equipment; and the wrong ground, it will introduce serious interference signal to PLC systems will not work.
Interference within the system from the PLC
Mainly by the system internal components and circuit interaction between electromagnetic radiation, such as logic circuits and their mutual radiation effects on analog circuits, analog with logic and compo
nents to the interaction between the use

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