Industrial production and the development of science and technology are inseparable from the PLC automation control, PLC can be broadly understood as: centralized relay extension control cabinet, the actual production applications, PLC greatly save the cost of industrial control, strengthen the centralized management of equipment and automatic control, want to learn PLC, the first PLC foundation needs to be solid.
1, from the composition of the PLC, in addition to the CPU, memory and communication interfaces, and the industrial field directly related to which interface? And explain its main functions.
(1) input interface: accept the signal of the controlled device, and through the photocoupling device and the input circuit to drive the internal circuit on or off.
(2) Output interface: the results of the program execution through the output interface photocoupler devices and output components (relays, thyristors, transistors) output, control of the external load on or off.
2, the basic unit of the PLC consists of which parts? What is the role of each?
(1) CPU: The core component of PLC directs PLC to perform various tasks. Such as accepting user programs and data, diagnostics, implementation of the executive program, etc.; (2) Memory: storage of data.
(2) Memory: Stores system and user programs and data.
(3) I / O interface: PLC and industrial production site is controlled by the connection between the object parts, used to accept the signals of the controlled device and output program results; (4) communication interface: PLC and industrial production site is controlled by the object parts, used to accept the signals of the controlled device and output program results.
(4) communication interface: through the communication interface and monitor, printer and other equipment for information exchange; (5) power supply.
(5) Power supply.
3, What types of PLC switching output interface? What are the characteristics of each?
Thyristor output type: in general, only with AC loads, fast response speed, high frequency of action.
Transistor output type: under normal circumstances, only with DC loads, fast response speed, high frequency of action.
Relay output type: in general, with AC and DC loads, but its response time is long, low frequency of action.
4, according to the structure of the type points, PLC which types? What are the characteristics of each?
(1) overall: the CPU, power supply, I / O components are concentrated in a chassis, compact, low price, generally small PLC using this structure; (2) Module: the module type: the CPU, power supply, I / O components are concentrated in a chassis, compact, low price, generally small PLC using this structure; (3) the PLC is not a module.
(2) modular: the various parts of the PLC is divided into a number of separate modules, according to the needs of different modules can be selected to form a system, with flexible configuration, easy to expand and maintain the characteristics of the general medium and large PLC using this structure. Modular PLC by the frame or substrate and a variety of modules, modules installed in the frame or substrate socket.
(3) Stacked: Combining the overall and modular features, stacked PLC CPU, power supply, I/O interfaces, etc. are independent modules, but they are connected by cable, making the system not only flexible configuration and compact size.
5, What is meant by PLC scan cycle? It is mainly affected by what?
PLC scanning process includes internal processing, communication services, input processing, program execution, output processing of five stages, these five stages of scanning the time required for a scan is called the scan cycle.
The scanning cycle is related to the CPU operation speed, PLC hardware configuration and the length of the user program.
6, PLC adopts what way to execute the user program? What are the stages of user program execution process?
PLC uses a cyclic scanning method to execute the user program, the user program execution process includes input sampling stage, program execution stage and output refresh stage.
7, PLC control system compared with the relay control system, what are the advantages?
(1) control method: PLC using the program to achieve control, easy to change or increase the control requirements, and PLC contacts unlimited; (2) the way of working: PLC using the program to achieve control, easy to change or increase the control requirements, and PLC contacts unlimited.
(2) the way of work: PLC using serial mode of operation, to improve the system's ability to resist interference; (3) the control speed: PLC using serial mode of operation, to improve the system's ability to resist interference.
(3) Control speed: PLC contacts are actually triggers, and the instruction execution time is in microseconds.
(4) Timing and counting: PLC adopts semiconductor integrated circuits as timer, the clock pulse is supplied by crystal, the delay time is high in accuracy and wide in range, PLC has the counting function which is not available in relay system; (5) Reliability and maintainability: PLC has the counting function which is not available in relay system.
(5) Reliability and maintainability: PLC adopts microelectronics technology, high reliability, with the self-test function to find out their own faults in time, monitoring function is convenient for debugging and maintenance.
8, PLC why the output response lag phenomenon? How to improve I/O response speed?
Because PLC adopts centralized sampling, centralized output cycle scanning mode of operation, the state of inputs can only be read in the input sampling stage of each scanning cycle, and the execution result of the program can only be sent out in the output refreshing stage; Secondly, the input and output delay of PLC, the length of user program, etc. can cause the output response hysteresis.
It is necessary to improve I/O sampling and output refreshing, or direct input sampling and output refreshing, as well as interrupting input and output and intelligent I/O interfaces.
9, What are the soft relays inside the FX0N series PLC?
Input relays, output relays, auxiliary relays, status registers, timers, counters, and data registers.
10,How to select PLC?
1) Model selection: should be from the structural form, installation, functional requirements, response speed, reliability requirements, model uniformity and other aspects to consider.
2) capacity selection: should be from the number of I / O points, the user's storage capacity of two aspects to consider.
3) I/O module selection: including switching and analog I/O module selection, as well as the selection of special function modules.
4) Selection of power supply module and other equipment such as programmer.
11, a brief description of the characteristics of the PLC centralized sampling, centralized output mode of operation, the use of this mode of operation has what are the advantages and disadvantages?
Centralized sampling: In a scanning cycle, the sampling of the input state is only carried out in the input sampling stage, and the inputs are blocked after entering the program execution stage.
Centralized Output: During a scan cycle, the state of the output image registers is transferred to the output latches only during the output refresh stage, and the outputs are stored in the output image registers during the rest of the scan cycle. Adopting this mode of operation can improve the anti-interference ability of the system and enhance the reliability of the system, but it will cause a lag in the response of the PLC input/output.
12, What kind of operation mode does the PLC use? What are the characteristics?
PLC adopts centralized sampling, centralized output and cycle scanning.
Characteristics: Centralized sampling means that in one scanning cycle, the PLC samples the input state only in the input sampling stage, and the input will be blocked when it enters the program execution stage.
Centralized output means that in one scanning cycle, the PLC only transfers the state related to the output in the output image register to the output latch in the output refresh stage, and refreshes the output interface, while the output state is always stored in the output image register in other stages.
Cyclic scanning means that the PLC needs to perform several operations in one scanning cycle, and it adopts a time-sharing scanning method to perform them one by one in sequence, and the operation is repeated from week to week.
13, Electromagnetic contactor mainly consists of which parts? Briefly describe the working principle of electromagnetic contactor.
Electromagnetic contactor generally consists of electromagnetic mechanism, contact, arc extinguishing device, release spring mechanism, bracket and base and other parts. Contactor according to the electromagnetic principle of work: when the electromagnetic coil is energized, the coil current generates a magnetic field, so that the static iron core generates electromagnetic suction to attract the armature, and drive the contact action, so that the normally closed contact is open, normally open contact is closed, the two are linked. When the coil is de-energized, the electromagnetic force disappears, and the armature drops under the action of the release spring, so that the contacts are restored, i.e., the normally open contacts are open and the normally closed contacts are closed.
14, Briefly explain the definition of programmable logic controller (PLC).
Programmable logic controller (PLC) is a specially designed for applications in industrial environments and digital operations of electronic devices. It uses a memory that can be programmed to store instructions to perform logical operations, sequential operations, timing, counting and arithmetic operations, etc., and can control various types of machinery or production processes through digital or analog inputs and outputs.
PLC and its related peripherals should be in accordance with the industrial control system is easy to form a whole, easy to expand its functions and design principles.
15, a brief answer to the PLC system and relay contactor system working principle of the difference.
Component devices are different.
The number of contacts is different.
Implementation of the control method is different.
The working method is different.
16, Mitsubishi FX 2N series PLC STL step ladder instruction has what characteristics?
(1) Automatic reset of the transfer source.
(2) Allow double output;
(3) Master control function.