The function of the touch screen is to control the soft relay of the PLC, for example, if you use X3 as the start, then you can connect X3 in parallel in the PLC program, for example, M45, set a virtual button in the touch screen, and then set it to M45 action in its characteristics, then when the touch screen and PLC are connected, press this button and press the practical button The effect is the same. The touch screen can also directly read and write the data register data in the PLC, which reflects the working status of the PLC and can vividly simulate the current working status of the machine, just like real-time monitoring. In short, in addition to the X point, the touch screen can control most of the soft components in the PLC, and in addition, the content of the touch screen must be one-to-one correspondence in the PLC.
The touch screen control station is called the upper computer in the automatic control, which is the human machine interface (hmi).
However, the touch screen does not have a CPU (no computing function), and the PLC is controlled by the touch screen in the industry, which is actually realized through configuration software.
For example, to put it simply, a switch quantity above the PLC has its own special method of indicating the program (generally the turn-on is called set, and the shutdown is called zero), and the corresponding thing may be a relay. So how do you control the relay to turn on in the program? It's the same principle as a touch screen. The program is stored in the CPU, and when the program is programmed, a specific switch will account for a "one" bit of switching signal in memory. When this switching signal (binary number) is 1, the CPU announces to the outside that the high-level trigger relay is energized, the loop at the other end of the relay is turned on, and the device is controlled.
The same is true for the graphics in the touch screen, a switch is set to two conditions, 1 when it is turned on, and 0 when it is turned off, when the CPU reads this signal through the network, the CPU will respond accordingly through the IO module to control the device to get power. In this way, ordinary users will have the illusion that the touch screen can control the device.
In fact, the real control of the equipment is composed of a demand current loop. It is controlled by a relay (in terms of switching output, the function of PLC is much greater than this). The relay blocks the high-voltage equipment and the PLC, and the low-voltage side is generally connected to the coil, and when the CPU reads 1, the coil is energized, and the coil is energized so that the thin piece of the relay is turned on, so that the high-voltage side is energized and constitutes its own circuit.
With CPUs, it is possible in industry to eliminate the need for wires in every location. This greatly reduces the cost, and the flexibility and scientificity of the operation are also greatly enhanced. Therefore, PLC is developed on the principle of relay, which is more advanced than the principle of relay. This is because the PLC comes with arithmetic logic units and so on. If you know the single-board computer, you will be able to understand the PLC. PLC is flexible to MCU.
In fact, as long as conditions permit, you can even use a mobile phone or remote control state-owned enterprises or other more abstract things to control the device.
Therefore, in order to realize touch screen control, there must be special personnel to configure the touch screen interface, which corresponds to the equipment I/O in the PLC
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