PLC is made up of which a few parts -

PLC by the CPU, power supply, input circuit, output circuit, storage and communication interface circuit several major part as shown

a PLC internal structure, CPU

PLC of the CPU is the central processing unit (CPU), actually can do all kinds of computing and data processing and the various input signals into the input register, and then by using the Boolean operation, timing, counting and arithmetic operation, data processing and transmission, communication network and a variety of operations, to compile and execute the command of the program, sends the results to the output side, to respond to all sorts of external devices.

PLC system, storage of a memory is mainly used for storing system program, the user program and working state data. The PLC controller memory including system program memory and user memory.

1。 System program memory ( ROM）

system program memory ( ROM） To the storage system management procedures, monitoring program and system internal data, PLC before delivery has its curing in read-only memory ROM or PROM, user can't change.

2。 User memory ( RAM)

RAM including user program memory ( Program area) And data storage ( Data area) Two parts.

RAM the temporary data storage, the intermediate result, and the user program. This type of memory generally have low power CMOS - RAM, can read and modify the storage content. After power off store content is missing, generally keep by lithium batteries. That is to say the user memory used to store the user control for specific tasks, PLC programming language programs.

user memory according to the choice of different types of memory ( Can be a block of RAM, EPROM and EEPROM memory) The software, the user can modify and increase or decrease. User data storage can be used to store the user use the ON/OFF state of the device and data, etc. , the user is related to the size of the user program memory storage capacity, the size of the is an important index of PLC performance.

PLC in order to read, write and modify the user program is stored in CMOS static RAM, with a continuous supply of lithium battery to keep the power, to ensure that the program will not be lost after useing.

the working data stored in RAM is often change during the process of PLC operation and often get some data, to meet the requirement of random access, working in the PLC data storage, has deposited in the input and output relay, auxiliary relay, counter, timer, such as logical data storage area, the status of the device are the initial value setting and running situation of the user program. According to the demand, some data in the power lost in the backup battery to maintain the existing state, this part can save data when power storage area called a data area.

switch input and output interface is connected to industrial field control electrical interface.

switch input and output interface adopts photoelectric isolation and RC filter, and realized the PLC electrical isolation of internal and external circuit, and reduce the electromagnetic interference, at the same time meet the need of industrial field of all kinds of signals matching.

, for example, switch input adopts photoelectric coupling circuit, interface circuit and the limit switch, manual switch, encoders, site input device control signals into the CPU can accept and digital signal processing.

1。 Input interface

input interface is used to accept, the acquisition of external input signal, and converts the signals into the CPU acceptable internal information.

input interface circuit can be collected signals have three categories, including active and passive switch and analog signals. Button, contactor contacts are passive, such as switch and travel switch, the proximity switch, transistor switch circuit and so on are the active switch, the analog signal is produced potentiometer, tachogenerator, and all kinds of transducer signal.

2。 Output interface

output interface circuit is a bridge between the PLC and the external load, to be able to PLC controller output signal is converted into outward can drive the external circuit control signal, in order to control such as contactor coils of electrical power.

switch output circuit including relay output, thyristor output and the transistor output three output form.

relay output slow response and large load capacity, each output of the maximum current is 2 a, can answer the dc or ac load.

transistor output response is fast, on load capacity is small, each output current in dozens of ma, can be connected dc load, equivalent circuit as shown in figure:

4

PLC, power supply module power supply module can be external input power after processing, into the PLC of the CPU, memory, input/output interface circuit inside the work needed to dc power supply.

many PLC controller adopts dc voltage switching power supply, dc power supply can not only provide a wide range of independent voltage for internal use, but also for the external input ( Such as sensors) Provide power supply, depending on the type of PLC, some use single ac power, the general is 220 v, some use dc power supply, generally for 24 v.

Professional plc controller price also understand that when you're working with programmable control systems product, it's important to understand that quality of plc manufacturers always matters.
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