Upper Machine refers to a computer that can directly issue control commands, usually a PC, displaying various signal changes (hydraulic, water level, temperature, etc.) on the screen.Lower Machine is a computer that directly controls devices and obtains their status, typically a PLC or microcontroller. Commands issued by the upper machine are first sent to the lower machine, which then interprets these commands into corresponding timing signals to directly control the relevant devices. The lower machine periodically reads the device status data (usually analog signals) and converts it into digital signals to feedback to the upper machine. In short, while the actual situations vary widely, the essence remains the same: both upper and lower machines require programming and have dedicated development systems.
The upper machine is also known as HMI (Human-Machine Interface, also referred to as Human-Machine Interface: with RS232, RS485, RJ45 network interfaces). Lower Machine is a computer that directly controls devices and obtains their status, typically a PLC or microcontroller. Commands issued by the upper machine are first sent to the lower machine, which then interprets these commands into corresponding timing signals to directly control the relevant devices. The lower machine periodically reads the device status data (usually analog signals) and converts it into digital signals to feedback to the upper machine. In short, while the actual situations vary widely, the essence remains the same: both upper and lower machines require programming and have dedicated development systems. Upper Machine commands are first sent to the lower machine, which then interprets these commands into corresponding timing signals to directly control the relevant devices. The lower machine periodically reads the device status data (usually analog signals) and converts it into digital signals to feedback to the upper machine. In short, while the actual situations vary widely, the essence remains the same: both upper and lower machines require programming and have dedicated development systems.
In concept, the controller and service provider is the upper machine, while the controlled and serviced entity is the lower machine. This can also be understood as the relationship between the master and slave, but the upper and lower machines can be interchangeable. How the two machines communicate generally depends on the lower machine. TCP/IP is generally supported. However, the lower machine typically has a more reliable proprietary communication protocol. When purchasing a lower machine, it comes with a large number of manuals and CDs that explain how to use the proprietary protocol for communication, often providing numerous examples that are generally straightforward for programmers, involving the use of some new APIs. Multi-language support modules generally support several high-level languages for upper machine programming.
Typically, communication between the upper and lower machines can use different communication protocols, such as RS232 serial communication or RS485 serial communication. When communicating between a computer and a PLC, not only can traditional D-type serial communication be used, but also more suitable industrial control communication like PROFIBUS-DP can be employed. Using packaged program development tools, communication between the PLC and upper machine can be achieved. Of course, one can also write their own driver-type interface protocol to control communication between the upper and lower machines.
1Definition of Human-Machine Interface Products
Connecting Programmable Logic Controllers (PLC), frequency converters, DC speed controllers, instruments, and other industrial control devices, using a display screen to show information, and through input units (such as touch screens, keyboards, mice, etc.) to write working parameters or input operational commands, achieving information interaction between humans and machines. It consists of hardware and software components.
2Composition and Working Principle of Human-Machine Interface (HMI) Products
Human-Machine Interface products consist of hardware and software components. The hardware part includes processors, display units, input units, communication interfaces, and data storage units. The performance of the processor determines the performance level of the HMI product and is the core unit of the HMI. Depending on the product grade of the HMI, processors can be selected from 8-bit, 16-bit, or 32-bit. HMI software is generally divided into two parts: the system software running on the HMI hardware and the screen configuration software running on a PC under the Windows operating system (such as JB-HMI screen configuration software). Users must first use the HMI screen configuration software to create an “engineering file,” which is then downloaded to the HMI processor via the serial communication port of the PC for execution.
1. What is the difference between a human-machine interface and what people commonly refer to as a “touch screen“?
Strictly speaking, there is an essential difference between the two. A “touch screen” is merely a hardware component that may be used in a human-machine interface product, serving as an input device that replaces some functions of a mouse and keyboard, installed at the front of the display screen; whereas a human-machine interface product is a device for human-machine interaction that includes both hardware and software. In industry, people often refer to human-machine interface products with touch input capabilities as “touch screens,” but this is not scientifically accurate.
2. What is the difference between a human-machine interface and configuration software?
Human-machine interface products, often referred to as “touch screens,” include HMI hardware and corresponding dedicated screen configuration software. Generally, different manufacturers’ HMI hardware uses different screen configuration software, with the main connected device type being PLC. Configuration software is a general tool software product running on a PC hardware platform and Windows operating system, which can also form an HMI product together with a PC or industrial computer; general configuration software supports a wide variety of device types, such as various PLCs, PC boards, instruments, frequency converters, modules, etc. Moreover, due to the powerful performance of the PC hardware platform (mainly reflected in speed and storage capacity), the functionality of general configuration software is also much stronger, suitable for large monitoring systems.
3. Do human-machine interface products have an operating system?
Any human-machine interface product has a system software component, which runs on the HMI processor and supports multi-task processing functions. The processor must have a small operating system to manage the operation of the system software. High-performance human-machine interface products based on tablet computers generally use common embedded operating systems such as WinCE and Linux.
4. Can a human-machine interface only connect to a PLC?
No, that is not the case. Human-machine interface products were developed to solve the human-machine interaction issues of PLCs, but with the advancement of computer technology and digital circuit technology, many industrial control devices now possess serial communication capabilities. Therefore, any industrial control device with serial communication capabilities, such as frequency converters, DC speed controllers, temperature control instruments, data acquisition modules, etc., can connect to human-machine interface products to achieve human-machine interaction functionality.
5. Can a human-machine interface only connect to other devices through standard serial communication ports?
In most cases, yes. However, with the development of computer and digital circuit technology, the interface capabilities of human-machine interface products are becoming increasingly robust. In addition to traditional serial (RS232, RS422/RS485) communication interfaces, some human-machine interface products now have network ports, parallel ports, USB ports, etc., allowing them to connect with industrial control devices that have network ports, parallel ports, USB ports, etc., to achieve human-machine interaction.
6. Do devices with communication capabilities necessarily connect with human-machine interface products?
That should be the case. General human-machine interface products provide a large number of commonly used device communication driver programs for selection. Generally, as long as the corresponding communication driver program is selected in the human-machine interface’s screen configuration software, communication between the HMI and the device can be established. If the selected HMI product’s configuration software does not have the communication driver program for the device to be connected, the user can inform the HMI product manufacturer of the communication port type and protocol content of the device to have the HMI manufacturer compile the communication driver program for that device.
7. Can a PC with a touch screen directly communicate with a PLC to complete HMI functions?
Of course, it can. However, corresponding HMI software must also be developed to make the PC a true HMI product.
8. What is the future development trend of human-machine interfaces?
With the advancement of digital circuits and computer technology, the future human-machine interface products will have increasingly blurred distinctions between high, medium, and low functions; the functionality of HMIs will become richer. HMI products larger than 5.7 inches will all feature color displays, and the lifespan of the screens will also be extended. Due to the decreasing costs of computer hardware, HMI products will primarily consist of high-end products based on tablet PCs, as these high-end products have significant advantages in processor speed, storage capacity, types and quantities of communication interfaces, networking capabilities, and software resource sharing, which is the future direction of HMI product development. Of course, small-sized (display size less than 5.7 inches) HMI products, due to their advantages in size and price, will see widespread application in human-machine interaction for small machinery as their functionality continues to enhance (such as adding I/O functions).