A, the power of the programmable logic controller power plays a very important role in the whole system.
Without a good, reliable power supply system is not work properly, therefore, programmable logic controller manufacturers also attaches great importance to power supply design and manufacturing.
General ac voltage fluctuation in the + 10% (
Range, can not take other measures to PLC communicate directly connected to the grid.
Second, the central processing unit (
The central processing unit (
Is the control center of the programmable logic controller.
It according to the function of the programmable logic controller system program to receive and storage from programmer type in the user program and data;
Check that the power supply, memory, I/O and warn the timer state, and diagnose the grammatical errors in the user program.
When programmable logic controller is put into operation, the first it receives in the form of scanning field state of each input device and data, and deposited in the I/O image area respectively, and then passes from the user program memory read the user program, after command interpretation shall be governed by the provisions of the directive arithmetic or logical operation into the I/O image area or the result of the data register.
After all of the user program is performed, the last I/O image area of each output state or output register data sent to the corresponding output device, so cycle run, until stop running.
In order to further improve the reliability of programmable logic controller, in recent years of large scale programmable logic controller also adopts double CPU redundancy system, the CPU or the use of three voting system.
In this way, even if a CPU fails, the whole system can still run normally.
Three, memory storage of system software known as the system program memory storage.
For application software called user program memory storage.
4 and 1 input/output interface circuit.
The input interface circuit and microcomputer by optical coupling circuit of the input interface circuit, the function is programmable logic controller and the control interface interface input channel.
Field output interface circuit by the output data registers, called the road and interrupt request circuit integration, the role of programmable logic controller through the output interface circuit to perform component output corresponding control signals on site.
Five, the function modules such as counting, positioning function module.
Six, communication module working principle: when a programmable logic controller after put into operation, its working process is generally divided into three stages, namely the input sampling, the user refreshes the three stages of program execution and output.
Complete the above three stages as a scan cycle.
During the whole operation, programmable logic controller CPU at a certain scanning speed repeat the above three stages.
The input sampling stage in the input sampling stage, programmable logic controller in scanning way in order to read all the input state and data, and put them into the corresponding cell in the I/O image area.
After the input sampling, transferred to the user program execution, and the output refresh stage.
In these two stages, even if the input state and data changes, the relevant unit I/O image area of the status and the data will not change.
Therefore, if the input is the pulse signal, the pulse signal must be greater than the width of a scan cycle, can ensure in any case, this input all can be read.
2, user program execution stage in the user program execution stage, programmable logic controller is always the sequence according to the top-down to scan a user program (
When scanning each ladder diagram, and always scan ladder diagram on the left side of the control circuit, composed of various contact and press the left right after the first, after the first order of composed of contact control circuit logic operations, and then according to the result of logic operation, refresh the logic coil in the system RAM memory area corresponds to a state;
Or refresh the output coil in the I/O image area corresponds to a state;
Or to determine whether or not to perform the function of the trapezoidal diagram of special instructions.
Namely, in the execution of a user program, the only input point in the I/O image in the state and the data will not change, while the other dots and soft devices in the I/O image area or the state of system RAM memory area and the data are likely to change, and in the ladder diagram above, the program execution results to row below those who use these coils or data of ladder diagram work;
On the contrary, the ladder diagram below, the competition for the logic state of the coil or data only on to the next scan cycle in the above procedure.
In the process of program execution if using I/O instructions immediately can directly access I/O points.
Using I/O instructions, the input process image register values will not be updated, application values directly from the I/O module, the output process image register will be updated immediately, with the input some differences immediately.
After the output refresh stage when scanning the user program, enter the output refresh stage programmable logic controllers.
During this period, the CPU according to the I/O image in the corresponding state and data refresh all the output latch circuit, then the output circuit drive corresponding peripherals.
At this moment, is the real output of programmable logic controller.