PLC control of the basic working principle, classification
The basic working principle of PLC
one). PLC with "sequential scanning, continuous cycle" work
1. Each scan process. Focus on the input signal sampling. Focus on the output signal to refresh.
2. Enter the refresh process. When the input port is closed, the program in the implementation phase, the input has a new state, the new state can not be read. The new state is read only when the next scan is made.
3. A scan cycle is divided into input samples, program execution, and output refresh.
4. The contents of the component map register are changed as the execution of the program changes.
5. The length of the scan cycle is determined by three.
(1) the speed at which the CPU executes the instruction
(2) the time of the instruction itself
(3) the number of instructions
6. Due to the use of centralized sampling. Centralized output of the way. There is a phenomenon of input / output hysteresis, that is, input / output response delay.
two). PLC and relay control system, computer distinction
1. Differences between PLC and relay control system
The former work is "serial", the latter work is "parallel".
The former with "software", the latter with "hardware".
2. Differences between PLC and Microcomputer
The former works by "cyclic scan". The latter works by "standby or interrupted"
3.PLC programming
The most prominent advantage of PLC is the use of "soft relays" instead of "hard relays". Use "software programming logic" instead of "hardware routing logic".
PLC programming language has ladder, Boolean mnemonic language, and so on. Especially the first two are commonly used. Classification of PLCs
C) by structure:
1. Integral: the PLC components are installed together or a few printed circuit boards, and together with the power supply installed in the chassis to form a single whole, called the host or the basic unit, small, ultra-small PLC This structure.
2. Modular: is the basic composition of the PLC made of independent modules. Medium, large PLC in this way. Easy to repair.
The basic working principle of PLC
one). PLC with "sequential scanning, continuous cycle" work
1. Each scan process. Focus on the input signal sampling. Focus on the output signal to refresh.
2. Enter the refresh process. When the input port is closed, the program in the implementation phase, the input has a new state, the new state can not be read. The new state is read only when the next scan is made.
3. A scan cycle is divided into input samples, program execution, and output refresh.
4. The contents of the component map register are changed as the execution of the program changes.
5. The length of the scan cycle is determined by three.
(1) the speed at which the CPU executes the instruction
(2) the time of the instruction itself
(3) the number of instructions
6. Due to the use of centralized sampling. Centralized output of the way. There is a phenomenon of input / output hysteresis, that is, input / output response delay.
two). PLC and relay control system, computer distinction
1. Differences between PLC and relay control system
The former work is "serial", the latter work is "parallel".
The former with "software", the latter with "hardware".
2. Differences between PLC and Microcomputer
The former works by "cyclic scan". The latter works by "standby or interrupted"
3.PLC programming
The most prominent advantage of PLC is the use of "soft relays" instead of "hard relays". Use "software programming logic" instead of "hardware routing logic".
PLC programming language has ladder, Boolean mnemonic language, and so on. Especially the first two are commonly used. Classification of PLCs
C) by structure:
1. Integral: the PLC components are installed together or a few printed circuit boards, and together with the power supply installed in the chassis to form a single whole, called the host or the basic unit, small, ultra-small PLC This structure.
2. Modular: is the basic composition of the PLC made of independent modules. Medium, large PLC in this way. Easy to repair.
评论
发表评论