1. Switch logic control replaces the traditional relay circuit to realize logic control and sequence control, which can be used for single machine control, multi-machine group control and automatic production line. Such as injection molding machine, printing machine, stapler, modular machine tool, grinder, packaging production line, electroplating production line, etc.
2. Industrial Process Control In the industrial production process, there are some continuously changing quantities (namely analog quantities), such as temperature, pressure, flow, liquid level and speed. PLC adopts corresponding A/D, D/A conversion modules and various control algorithm programs to process analog signals and complete closed-loop control. PID regulation is a widely used regulation method in general closed-loop control system. Process control is widely used in metallurgy, chemical industry, heat treatment, boiler control and other occasions.
3. Motion control PLC can be used to control circular motion or linear motion. Generally, special motion control modules are used, such as single-axis or multi-axis position control modules that can drive stepping motors or servo motors, which are widely used in various machinery, machine tools, robots, elevators and other occasions.
4. Data processing PLC has the functions of mathematical operation (including matrix operation, function operation and logic operation), data transmission, data conversion, sorting, table lookup and bit operation, and can complete data acquisition, analysis and processing. Data processing is generally used in some large-scale control systems, such as papermaking, metallurgy, food industry and so on.
5. Communications and networks
PLC communication includes communication between PLCs and communication between PLCs and other intelligent devices. With the development of factory automation network, now PLC has communication interface, and communication is very convenient.
Third, the application characteristics of PLC
1. High reliability, strong anti-interference ability and high reliability are the key properties of electrical control equipment-PLC has high reliability because it adopts modern large-scale integrated circuit technology and strict production technology, and its internal circuit adopts advanced anti-interference technology. Compared with the relay contactor system of the same scale, the electrical wiring and switch contacts are reduced to hundreds or even thousands, and the faults are greatly reduced. In addition, PLC has the function of hardware fault self-checking, which can send out alarm information in time when there is a fault. In the application software, users can also write the fault self-diagnosis program of peripheral equipment, so that the circuits and equipment in the system except PLC can also obtain fault self-diagnosis protection. In this way, the whole system will be extremely reliable.
2. Complete facilities, perfect functions and strong applicability-PLC has developed to today and has formed a series of products of various scales, which can be used in industrial control occasions of various scales. In addition to the logic processing function, PLC mostly has perfect data operation ability, which can be used in various digital control fields. A large number of functional units emerge, which makes PLC penetrate into various industrial controls such as position control, temperature control and CNC. Coupled with the enhancement of PLC communication ability and the development of man-machine interface technology, it is very easy to form various control systems with PLC.
3. Easy to learn and easy to use, welcomed by engineers and technicians-PLC is the industrial control equipment of industrial and mining enterprises. Its interface is simple, and the programming language is easily accepted by engineers and technicians. The graphic symbols and expressions of ladder diagram language are quite close to relay circuit diagram, which opens the door for people who are not familiar with electronic circuits, computer principles and assembly language to engage in industrial control.
4. The design of the system has the advantages of small workload, convenient maintenance and easy transformation-PLC uses storage logic instead of wiring logic, which greatly reduces the external wiring of control equipment, greatly shortens the design and construction cycle of control system, and makes daily maintenance easier. More importantly, it makes it possible for the same equipment to change the production process by changing the program. This is especially suitable for multi-variety and small batch production. [Edit this paragraph] What are the reasons for the PLC crash? There are many reasons for PLC crash, and errors in software and hardware may lead to the crash. 1, hardware
(1) I/O channel, PLC automatically detects I/O errors and enters the stop mode.
(2)I/O is damaged, the program runs to the place where I/O feedback signal is needed, and the instruction cannot be executed downwards.
(3) Line interference or open circuit of expansion module (functional type, such as A/D).
(4) The power supply is disturbed or faulty.
(5) 5) The connection module and address allocation module of PLC are faulty.
(6) Faults caused by cables.
2. Software.
(1) triggered an infinite loop.
(2) The program rewrites the contents of the system parameter area, but there is no initialization part.
(3) Protection program startup: hardware protection and limited use time (used to recover payment)
(4) Data overflow, excessive step size and watchdog (dog time can be modified) action.
Repair and maintenance of PLC
A, maintenance procedures, equipment testing and adjustment rules on a regular basis
(1) Check the connection of terminals in the PLC cabinet once every six months or once every quarter, and reconnect them in time if they are loose;
(2) Re-measure the working voltage of the host power supply in the cabinet every month;
Second, the provisions of the regular cleaning of equipment
(1) Clean the PLC once every six months or every quarter, cut off the power supply of the PLC, remove the power rack, CPU motherboard and input/output board in turn, purge them, then install them in place in turn, restore all connections, and then power on the PLC host. Carefully clean the sanitation in the PLC box;
(2) Replace the filter screen under the power frame every three months; Third, preparation before maintenance, maintenance procedures (1) Prepare tools before maintenance; (2) In order to ensure that the components do not fail and the templates are not damaged, protective devices must be used, and anti-static preparations should be made carefully;
(3) Contact the dispatcher and operators before maintenance, and hang the maintenance card when necessary;
Fourth, the sequence and method of equipment disassembly
(1) Stop the machine for maintenance, and there must be two or more people to monitor the operation;
(2) Turn the mode selection switch on the front panel of CPU from the "run" position to the "stop" position;
(3) Turn off the main power supply of PLC, and then turn off other power supplies of Moban;
(4) Write down the number and connection position of the power cord connecting the power rack, and then remove the screws connecting the power rack and the cabinet, so that the power rack can be removed;
(5) The CPU motherboard and I/O board can be removed by rotating the screws under the template;
(6) Installation shall be carried out in the reverse order;
V. Maintenance Process and Technical Requirements
(1) When measuring voltage, use a digital voltmeter or multimeter with an accuracy of 1%.
(2) The power rack and CPU motherboard can only be disassembled when the main power supply is cut off;
(Before the RAM module is taken out of or inserted into the CPU, the power of the PC should be disconnected to ensure that the data is not confused;
(4) Before disassembling the RAM module, check whether the battery of the module works normally. If the battery fault light is on, the PAM content of the removed module will be lost;
(5) The main power supply should also be turned off before removing the I/O board, but if production needs it, the I/O board can also be removed while the programmable controller is running, but the QVZ (timeout) light on the CPU board is on;
(6) When inserting the template, be extra careful, handle it with care, and carry away the items that generate static electricity;
(7) Replacement parts shall not be operated with electricity;
(8) After maintenance, the formwork installation must be in place.
PLC is mainly suitable for the control core with small batch and changeable process equipment, so as to shorten the development cycle and quickly apply it to production.