Is programmable logic controller PLC full name of the English abbreviation, in Taiwan area referred to as 'can Cheng Qi', according to the name of its role is mainly used to implement the industrial logic control.
Early automation can be divided into industrial electrical automation, automatic control automation and production process automation, only industrial automation PLC to study this course, so visible PLC focuses on application in the electric control system.
earlier, there is no price is more expensive, PLC or PLC controller
logic control basically is to use the relay and contactor.
Relay or contactor is a coil with a few road normally open or normally closed contacts, the use of self-preservation and between the coil and contact interlock to combine a variety of complex industrial control logic, such as machine tool control, to start the motor and reversing, to cooperate with each other, between the shaft to turn colder liquid circulating pump, to make the drive rev. Stop, with a lot of relay.
Logic is divided into combinatorial logic and temporal logic, relay implementation combinational logic is easy, but the implementation temporal logic is a little difficult, after all, time relay is relatively rough.
because of relatively large volume of relay and contactor, so complex logic, design difficulty, want to consider a number of circuit loop, a bit not careful is wrong;
Installation is also trouble, want to use a lot of electrical cabinet, layout is not easy.
Debugging is a painful thing, modify the line, because encountered very prone to errors;
Much more to worry about maintenance, line, dazzle you, relay has certain life cycle, let whole maintenance electrician vexed problem such as poor contact.
electronic technology developed, single machine appeared, and then people try to use a single machine to replace the relay circuit, the result is very complex logic, as long as the integration on a board can meet the functional requirements.
So the industrial electrical system can realize more complex logic control, small volume, it's much more easier than relay to maintain.
But not single machine reliability, industrial sites need strong anti-interference, dust and vibration is also very severe, and the use of assembly language programming, general electrician can not learn.
single chip microcomputer, the function of the single machine basically is integrated into one chip, so there's a company called modicon PLC was designed, the product out, considering the requirement of industrial sites, hardware processing is stable and reliable, and then the software
according to the electrician habits of thinking, make a set of ladder diagram programming system, and the relay circuit is the same as the offline, so 'connection' on the computer, in accord with to replace the physical, can realize the 'soft' method to modify the logic circuit.
design inside the counter and timer, so avoid the trouble of the timer and time relay, modify the count and the duration is very convenient, the previous traditional relay difficult temporal logic control is done very accurate.
Even some bosses worry that customers don't give money, use the calendar to set a clock, dong zhong run to a certain time points a seconds, partial function will stop automatically.
in the field of industrial control, as long as it is to use logic control device, can use PLC to realize.
Such as metallurgy, plastics, wood, water treatment, chemical industry, petroleum, building materials, electric power, electrical appliances and so on, almost all areas, as long as there is the occasion of automation equipment, PLC is used, and some civilian areas, such as security, transportation, intelligent household is also using PLC, etc.
early PLC just can complete logic control, but the chips and electronic technology is developing very fast, PLC increased the analog processing capabilities, the analog sensor can directly read data, it can be used to do some data collection and monitoring, if the data is used to control frequency converter device, and can achieve some goals closed-loop control.
PLC increased high-speed count function, can realize some parameters such as length measurement, as well as high-speed pulse output, can be used to control the servo and stepper positioning controller.
PLC operation speed is fast, can be in inside oneself write some PID or fuzzy algorithm function, can be used to do some complex control loop, and even some PLC itself with the PID module, direct call.
PLC also integrates all kinds of communication interface such as 485232 and RJ45 these, can be achieved and inverter, touch screen, temperature control modules, industrial control products such as communication network.
PLC to increase the function of these, many aspects have replaced the controller inside the process control field, only need to add a function module and PLC, can easily achieve the function of the traditional controller some, some large function of PLC to realize, how much worse than DCS system.
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