The characteristics of the PLC programmable controller, PLC) The characteristics of

In order to adapt to industrial environment, compared with general control device, PLC machine has the following characteristics: 1. High reliability, strong anti-interference ability of industrial production control equipment reliability requirements: (1) the average time between failures long (2) the failure time to repair ( Mean time to repair) Short of any electronic equipment, usually in the form of two kinds: (1) accidental failures. Due to the external environment such as electromagnetic interference, ultra high temperature, cryogenic, overvoltage, undervoltage, vibration caused by the fault. This kind of failure, as long as it doesn't cause damage to system components, once back to normal environmental conditions, system is back to normal. But for PLC, affected by the outside world, the internal storage of the information may be damaged. (2) a permanent fault. Because components unrecoverable damage caused by failure. If we can limit the occurrence of accidental fault conditions, if we can make the PLC in the bad environment can not be affected or limit the consequences of impact in the minimum range, PLC in bad conditions disappear automatically after returned to normal, so it can improve the average time between failures; If the PLC can increase some diagnostic measures and appropriate means of protection, in permanent fault occurs, can quickly find out failure points, and limit failure in local, can reduce the mean time to repair of PLC. To this end, the PLC manufacturers adopted many measures in hardware and software aspects, make the PLC besides itself has strong ability of self diagnosis, timely give error messages, stop running outside waiting for repair, also make PLC has strong anti-interference ability. Hardware measures: main module adopts large or very large scale integrated circuit, a large number of switch actions performed by the non-contact electronic memory, I/O system design with perfect channel protection and signal conditioning circuit. (1) block - — For power transformer, CPU, programmer, such as main components, conductive, permeability good material for shielding, in case of interference. (2) filter - — For power supply system and input circuit adopts various kinds of filter, such as LC or PI type filter network, in order to eliminate or suppress the high frequency interference, also weakened the interaction between the various modules. (3) the power adjustment and protection - — The microprocessor, the core components required to + 5 v power supply, using multilevel filter, and the integrated voltage regulator to adjust, to adapt to the ac grid fluctuation and the influence of the overvoltage, undervoltage. (4) isolation - — Between the microprocessor and the I/O circuit, using photoelectric isolation measures, effectively isolate the I/O interface between the CPU and electrical connection, reduce the fault and error action; Between the I/O port is insulated from each other. (5) adopts modular structure - — This structure will help in fault cases short-term fix. Once found a module failure, can quickly change, make the system back to normal work; At the same time can also help to search the cause of the problem. Software measures: strong self-checking and protection function. (1) fault detection - — Software testing environment on a regular basis, such as electricity, owe voltage, lithium battery voltage is too low and strong interference signal, etc. In order to timely processing. (2) the information protection and recovery - — When there is an accidental fault conditions, does not destroy the PLC internal information. Once fault conditions disappear, then back to normal, to keep working on the original program. So, PLC when the fault condition is detected, immediately save now state in memory, cooperate to closed storage software, prohibit any operation of storage, in case the stored information was washed away. (3) set the alarm clock WDT ( Watchdog) — — If the program execution time per cycle than the time stated on the WDT, announced a program into an infinite loop, immediately report to the police. (4) strengthen the inspection and calibration of application - — Once the program is wrong, and immediately report to the police, stop execution. (5) to the program and dynamic data of battery backup - — After the blackout, using the backup battery power, the state and the information is not lost. PLC factory test projects, one is the anti-jamming test. It requires that can withstand the amplitude is 1000 v, 1 ns rise time, pulse width for 1 mu S interference pulse. In general, the average time between failures can reach hundreds of thousands to tens of millions of hours; Made system can be up to 4 ~ 50000 hours or longer. 2. Strong commonality, variable control program, easy to use a variety of hardware of PLC variety complete device, can form can satisfy various requirements of the control system, the user does not have to own design and production of hardware devices. Users in the hardware to determine later, in the production process to change or update production equipment, don't need to change the PLC hardware equipment, by reprogramming can meet the requirements. As a result, PLC in addition to the application in the single machine control, also is widely used in factory automation. 3. Not only has strong function, adaptation of wide modern PLC logic, timing, counting, sequence control and also with digital and analog input and output, power, communication, man-machine dialogue, self-checking, according to records, etc. Can control a production machinery, a production line, and can control a production process. 4. PLC programming is simple, easy to grasp the current, most are still controlled by relay in the form of 'ladder diagram programming way'. Both inherited the traditional control lines clear and intuitive, and given that most factories in electrical technical personnel's habit of reading and programming level, so it is easy to accept and grasp. Ladder diagram programming language element symbols and expressions and relay control circuit principle diagram is quite close. By reading the PLC user manual or short-term training, electrical technicians and technical workers will soon be able to learn to use ladder diagram of control program. At the same time also provides a functional diagram, statement table such as programming language.