I. Definition of PLC
Programmable logic controller (Programmable Logic Controller) referred to as PLC, which is defined as: designed specifically for applications in industrial environments and a digital computing operations of electronic systems. It uses a class of programmable memory, used to store the user program, the implementation of logical operations, sequence control, timing, counting and arithmetic operations and other user-oriented instructions, and through the digital or analog inputs and outputs to control various types of machinery or production processes.PLC is based on microprocessors, a combination of computer technology, automated control technology and communications technology to develop a general-purpose industrial automatic control device. PLC is a general industrial automatic control device based on microprocessor and integrating computer technology, automatic control technology and communication technology. With the progress of science and technology and the continuous development of programmable controllers, functions continue to increase, the definition will change.
II. the structure of the PLC composition
Programmable controller is essentially a special computer for industrial control, the actual composition of the system and microcomputer is basically the same, generally consists of the following five parts:
1. Central processor. Logical and mathematical operations, control the entire system, so that it works in a coordinated manner;
2. Memory. Used to store the system's monitoring program, user program, logic variables and some other information;
3. Interface circuit. It is the PLC and field devices and peripheral equipment contact channel, such as input / output interface, keyboard / display interface, communication interface and expansion interface, and so on;
4. Input and output circuits. Input circuit is used to isolate the input signal and level conversion; output circuit is used to amplify the output of the PLC and level conversion, drive field devices;
5. Power supply. Including the system power supply, standby power and power-down protection power supply.
III. the working principle of PLC
PLC uses a different way of operation from the general microcomputer - scanning technology. When the PLC is put into operation, its work is completed in a cyclic scanning mode, generally divided into three stages, namely, input sampling, user program execution and output refresh three stages. The completion of the above three stages is called a scanning cycle. During the entire operation, the PLC CPU to a certain scanning speed to repeat the above three stages, a cycle of time used for: T = (read time * input points) + (computing speed * program steps) + (output time * output points) + self-diagnostic time, touch-screen technology in the PLC applications
Users need to set the amount of voltage, frequency of the target value, which is the use of dip switches digital setting input area to achieve this purpose. The user can directly increase or decrease the operation on the dip switches to get the desired target value. After setting on the dip switches, clicking the "OK" button, the value is sent to the PLC target value saving unit, and clicking the "Cancel" button, the original value remains unchanged, and the multiple of the value, the precision, and the address of the value in the intrinsic unit of the PLC are set in the properties of the dip switches. The multiplier, the precision and the address of the value in the inner unit of the PLC are set in the properties of the dip switches.
According to the working principle, the touch screen can be divided into four categories: infrared sensor, surface acoustic wave, capacitive sensor and resistive pressure, and different working principles will determine the response time, positioning accuracy and working environment of the touch screen. In foreign countries, touch screen technology has been quite mature, in Europe and the United States, such as: Micro Touch, ELO and Dynapro and other manufacturers have nearly two decades of manufacturing history; Japan's Nisha, Gunze and so on have more than 10 years of production experience. In the development of product technology, the East and West are different, Europe and the United States to capacitive touch screen, surface acoustic wave type and five-wire resistive development direction, the product to the majority of large-sized products; Japan's touch-screen technology is four-wire resistive as the main direction of development, the product to the small and medium-sized as the main goal; Taiwan and South Korea, most of the manufacturers are close to the footsteps of the Japanese to the development of the four-wire resistive majority.
Touch is one of the simplest and most instinctive common behaviors of human beings. There are many reasons to use touch technology, including in kiosk-type applications to limit end-user access to the computer, but also the need for data entry and computer sealing, protection between the two trade-offs between the harsh environment. Touch screens work by dividing the screen image area into a pre-determined grid (largely dependent on screen size and resolution). Touching a quadrant of a menu option executes a subroutine with the same effect as using a mouse or typing a command at the prompt line. There are five components involved in touchscreen technology: the touch sensor, the LED display, the controller, the software driver, and the CPU in the touchscreen. touchscreens are the simplest and most direct way to achieve interaction between the user and the computer. Although touchscreen technology is relatively new, the basic way users interact with touchscreens has been around for a very long time: your hand reaches out for what you want, which is the instinct of almost all children and adults. Companies in a wide range of industries have successfully utilized the utility of touchscreens in their own applications.
Airlines use it to simulate the cabin and train pilots to fly the plane; touchscreens on locomotives are used to display the status of train operations in all directions; real estate companies use it to enable home buyers to view full-color images of commercial properties at the snap of a finger; restaurants use it to streamline in-store POS terminals; and bank ATMs use it to simplify the operation of users' withdrawals and deposits.
Across all industries, the substantial benefits of touchscreen technology remain the same: touchscreens allow users to operate the host computer immediately without any training, and without specialized training in computers. The use of touchscreens virtually eliminates the possibility of operator error due to the clear menu settings available to the user. Touch screen in the true sense of the input and output devices to achieve the integration of the success of its replacement of the keyboard and mouse, strong and durable, can withstand the harsh environment of the keyboard and mouse are vulnerable to damage through the touch screen can quickly access all types of digital media, will not be hindered by text-based interfaces; the use of the touch screen to ensure that the space will not be wasted because the input devices have been fully integrated into the display.