As we all know, industrial production and the development of science and technology are inseparable from the automation control of PLC, 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 photocoupler device and the input circuit to drive the internal circuit on or off.
(2) output interface: the results of program execution through the output interface photocoupler devices and output components (relays, thyristors, transistors) output, control the external load on or off.
2, PLC's basic unit consists of which parts? What is the role of each?
(1) CPU: the core component of the PLC, the command PLC for a variety of work. Such as accepting user programs and data, diagnostics, implementation of the executive program, and so on.
(2) memory: storage system and the user's program and data.
(3) I / O interface: PLC and industrial production site is controlled by the object of the connection between the components, used to accept the signals of the controlled device and the output program execution results.
(4) communication interface: through the communication interface with the monitor, printer and other devices for information exchange.
(5) power supply.
3, What types of PLC switching output interface? What are the characteristics of each?
Thyristor output type: under normal circumstances, 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.
4, according to the structure of the type points, PLC which types? What are the characteristics of each?
(1) the whole type: the CPU, power supply, I / O components are concentrated in a chassis, compact, low price, generally small PLC using this structure; 2) module type: the CPU, power supply, I / O components are concentrated in a chassis, compact, low price, generally small PLC using this structure.
(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: a combination of integral and modular features, stacked PLC CPU, power supply, I / O interfaces, etc. are also independent modules, but they are connected by cable, making the system not only flexible configuration and compact size.
5, what is called 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, the five stages of scanning the time required is called the scan cycle.
Scan cycle with the CPU operating speed, PLC hardware configuration and the length of the user program.
6, PLC using what way to execute the user program? User program execution process includes what stages?
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.
(3) control speed: PLC contacts are actually triggers, instruction execution time in microseconds.
(4) timing and counting: PLC uses semiconductor integrated circuits as a timer, the clock pulse provided by the crystal, high precision delay, wide range; PLC has a relay system does not have the counting function; (5) reliability and maintainability: PLC has a relay system does not have the counting function; PLC has a relay system does not have the counting function.
(5) reliability and maintainability: PLC microelectronics technology, high reliability, with the self-test function can be found in time.
8, PLC why the output response lag phenomenon? How to improve I / O response speed?
Because the PLC uses a centralized sampling, centralized output cycle scanning mode of operation, the state of the inputs only in each scanning cycle of the input sampling stage can be read, and the results of the program execution only in the output refresh stage to be sent out; the second PLC input and output delay, the length of the user program can be caused by the lag in the output response.
To improve the I / O sampling, output refreshing, or direct input sampling, output refreshing, as well as interrupt the input and output and intelligent I / O interface and other ways.
9, Siemens series PLC internal soft relays which are?
Input relays, output relays, auxiliary relays, status registers, timers, counters, data registers.
10,How to choose PLC?
(1) model selection: should be considered from the structure of the form, installation, functional requirements, response speed, reliability requirements, model unity and other aspects;.
(2) capacity selection: should be from the I / O points, the user 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) power supply modules and programmers and other equipment selection.
11, a brief description of the PLC centralized sampling, centralized output mode of operation, the use of this mode of operation has what advantages and disadvantages?
Centralized sampling: in a scanning cycle, the input state of the sample only in the input sampling stage, when entering the program execution stage after the input will be blocked.
Centralized output: In a scan cycle, only in the output refresh stage will the output image register related state be transferred to the output latch to refresh the output interface, in other stages the output state has been stored in the output image register. The use of this mode of operation can improve the system's anti-interference capability, enhance system reliability, but will cause the PLC input / output response lag.
12, PLC using what kind of work? What are the characteristics?
PLC using centralized sampling, centralized output, cycle scanning mode of operation.
Characteristics: centralized sampling refers to a scanning cycle, PLC input state sampling only in the input sampling stage, when entering the program execution stage after the input will be blocked.
Centralized output means that in a scan cycle, the PLC only in the output refresh stage will be the output image register and the output of the state of the transfer to the output latch, the output interface to refresh, in other stages of the output state has been saved in the output image register.
Cyclic scanning refers to the PLC in a scanning cycle needs to perform multiple operations, it uses a time-scanning method in order to perform one by one, repeated week after week.
13, electromagnetic contactor mainly consists of which parts? Briefly describe the working principle of electromagnetic contactor.
Electromagnetic contactor is generally composed 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 produces electromagnetic suction to attract the armature, and drive the contact action, so that the normally closed contacts open, normally open contacts closed, the two are linked. When the coil is de-energized, the electromagnetic force disappears, the armature in the release of the role of the spring is lowered, so that the contact recovery, that is, the normally open contacts open, normally closed contacts closed.
14, briefly programmable controller (PLC) definition.
Programmable logic controller (PLC) is a specially designed for applications in industrial environments and digital computing 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, 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 extend the principle of its function and design.
15, short answer PLC system and relay contactor system working principle of the difference.
Component devices are different.
The number of contacts is different.
The implementation of different methods of control