The content of the PLC system design

One, the input circuit design 1 power supply, power supply circuit of PLC is commonly AC85 - 240 v ( There is also a DC24V) Wide, adapt to the power supply, but for the sake of anti-interference, purification should be equipped with power supply components ( Such as power supply filter, 1:1 isolation transformer, etc. ) 。 2, the use of PLC DC24V power supply companies PLC products usually have DC24V power supply, small, but the power capacity for tens of hundreds of ma, ma to use to pay attention to when its load capacity, at the same time get short circuit measures ( Because of overload or short circuit of the power supply will affect the operation of the PLC) 。 If 3, external DC24V power input circuit of DC24V power supply close to switches, photoelectric switch, etc. , and PLC DC24V power supply capacity is not enough, to provide DC24V power supply from outside; But the power supply '- 'End and PLC DC24V don't' - 'Side and'. com 'and is linked together, otherwise it will affect the operation of the PLC. 5 ma, therefore, when the input circuit of series diode or resistance ( Can't start) , or when a parallel resistance or leakage current ( Can't completely cut off) , it will be wrong action, reduced sensitivity, measures should be taken to this. On the other hand, when the input device, the input current is greater than the PLC input current, the biggest can also cause misoperation, should use low current input device, and choose to lose artificial leak type input of PLC, Bp's public input elements relative to negative potential, the input current is out of PLC. Second, the output circuit design, the comparison between various output mode (1 1) Relay output: advantage is that can bring different between different common point load, ac or dc voltage can also be different, and load current can be up to 2 a/point; But the relay output is not suitable for high frequency load action, this is decided by the life of the relay. Its life takes load current increase and decrease, generally between the hundreds of thousands of times to Jl one million times, some products can reach more than 10 million times, the response time of 10 ms. ( 2) Thyristor output: on load capacity of 0. 2 a/point, can only take ac load, can adapt to the high frequency motion, the response time of 1 ms. ( 3) Transistor output: the biggest advantage is adapted to the high frequency motion, short response time and generally to 0. About 2 ms, but it can only take DC 5 - 5 a/point, but each 4 points shall not be greater than zero. 8A。 When your system output frequency for 6 times per minute, should be the preferred relay output, because of its simple circuit design, strong anti-interference and load capacity. When the frequency is below 10 times/min, relay output can be used both ways; Can also be driven by PLC output darlington transistor ( 5 - 10) , and then driving load, can be greatly reduced. 2, anti-jamming and external interlock when PLC output with perceptual load and power load when the PLC output surge current impact, therefore, the dc load should be in the side and in the flow diode, perceptual load on communication should be and surge absorbing circuit, which can effectively protect the PLC. When two quantities of output in the PLC internal software has been obtained, interlock, also should undertake the outside of the PLC interlock, to enhance the reliability of the system. 3, 'GOM' point to select different PLC controller products, the number of its '. com 'point is not the same, or a'. com 'point to take eight dots, some with 4 dots, also have take 2 or 1 dots. When the load variety, and current is big, adopt a '. com 'point to take 1 - 2 the output points of PLC products; When the load quantity and types, using a '. com 'with 4 - Eight output points of PLC controller products. This will bring many convenient for circuit design, each '. com 'point to add a fuse, 1 - 2 2 a fuse, the output of the 4 - At 8 o 'clock the output plus 5 - 10 a fuse, because there is no fuse inside the PLC. 4, PLC external drive circuit for PLC output cannot be directly drive the load cases, must be adopted in the external drive circuit: can use triode, also can use solid state relay or thyristor driving circuit, protection circuit and surge absorbing circuit should be adopted at the same time, and each road has shown diode ( 领导) Instructions. PCB should make plug type, easy to maintenance. PLC input and output wiring also to have certain request, please see the instruction for use of the company. Don't need to extend commonly; When the system is large, will be extended. Different products, the number of total points of the system and extension module has a limit, when the extension still cannot meet the requirements, the network structure can be used; At the same time, some manufacturers of individual instruction does not support extension module, therefore, should pay attention to when to software establishment. When the temperature simulation module, each manufacturer has some rules, please see the relevant technical manuals. The company has a variety of extension modules, such as single input module, output module, input and output module, temperature module, high-speed input module, etc. PLC of this modular design provides convenience for the user's product development. Four, PLC network design when using PLC controller network design, its difficulty is much bigger than the PLC unit control. First of all, you should choose yourself more familiar with the model, the basic instructions and functions have a deeper understanding, and instruction execution speed and user program storage capacity should also be careful about. Otherwise, cannot meet the real-time requirements, you cause a system crash. In addition, the communication interface, communication protocol and data transfer speed also want to consider.
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