8. Why does PLC produce output response lag? How to improve I/O response speed?
Because the PLC adopts the cyclic scanning mode of centralized sampling and centralized output, the state of the input terminal can only be read in the input sampling stage of each scan cycle, and the execution result of the program is only sent out in the output refresh stage; secondly, the PLC input , output delay delay, the length of the user program, etc. can cause output response delay.
To improve I/O input sampling, output refresh, or direct input sampling, output refresh, and interrupt input and output and intelligent I/O interface and other methods.
9. What kinds of soft relays are there in FX0N series PLC?
Input relays, output relays, auxiliary relays, status registers, timers, counters, data registers.
10. How to choose PLC?
1) Model selection: It should be considered from several aspects such as structural form, installation method, functional requirements, response speed, reliability requirements, and model unity;
2) Capacity selection: should be considered from the two aspects of I/O points and user storage capacity;
3) I/O module selection: including switch and analog I/O module selection, as well as special function module selection;
4) Selection of other equipment such as power supply module and programmer.
11. Briefly describe the characteristics of PLC centralized sampling and centralized output work mode, what are the advantages and disadvantages of adopting this work mode?
Centralized sampling: in one scan cycle, the sampling of the input state is only performed in the input sampling stage, and the input terminal will be blocked when entering the program execution stage.
Centralized output: in one scan cycle, only in the output refresh stage, the output-related state in the output image register is transferred to the output latch, and the output interface is refreshed, and the output state is kept in the output image in other stages. in the register. Adopting this way of working can improve the anti-interference ability of the system and enhance the reliability of the system, but it will cause the lag of PLC input/output response.
12. What kind of working method does PLC adopt? What are the characteristics?
PLC adopts the working mode of centralized sampling, centralized output and cyclic scanning.
Features: Centralized sampling means that in one scan cycle, the PLC samples the input state only in the input sampling stage, and the input end will be blocked after entering the program execution stage.
Centralized output means that in one scan cycle, the PLC only transfers the output-related state in the output image register to the output latch in the output refresh stage, and refreshes the output interface, and the output state is always saved in other stages. in the output image register.
Cyclic scan means that the PLC needs to perform multiple operations in one scan cycle. It uses the time-sharing scan method to perform one by one in sequence, and runs repeatedly.
13. What are the main parts of the electromagnetic contactor? Briefly describe the working principle of electromagnetic contactor
Electromagnetic contactor is generally composed of electromagnetic mechanism, contacts, arc extinguishing device, release spring mechanism, bracket and base.
The contactor works according to the electromagnetic principle: when the electromagnetic coil is energized, the coil current generates a magnetic field, which makes the static iron core generate electromagnetic attraction to attract the armature, and drives the contacts to act, so that the normally closed contacts are disconnected and the normally open contacts are closed. linked. When the coil is powered off, the electromagnetic force disappears, and the armature is lowered and released under the action of the release spring, so that the contact is restored, that is, the normally open contact is disconnected, and the normally closed contact is closed.
14. Briefly describe the definition of programmable logic controller (PLC)
A Programmable Logic Controller (PLC) is an electronic device specially designed for digital operation in industrial environments. It uses a programmable memory to store instructions for performing logical operations, sequential operations, timing, counting and arithmetic operations, and can control various types of digital or analog inputs and outputs. Mechanical or production process.
PLC and its related peripheral equipment should be designed according to the principle that it is easy to form a whole with the industrial control system, and it is easy to expand its functions.
15. Briefly answer the difference between the working principle of PLC system and relay contactor system
The components are different;
The number of contacts is different;
Different methods of implementing controls;
Works differently.
16. Short answer What are the characteristics of the STL stepping ladder instruction of Mitsubishi FX 2N series PLC?
(1) The transfer source is automatically reset;
(2) Double output is allowed;
(3) Main control function.
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