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Do You Really Understand Human Machine Interface (HMI) - HMI Q&A

Nov 03, 2021

Q1: Is HMI only used to connect to PLC?

That’s not true. HMI products are originally produced to solve the problem of PLC human-computer interaction. But with the development of computer technology and digital circuit technology, much industrial control equipment has a serial communication interface ability. So as long as there is a serial communication interface ability of the industrial control equipment, such as VFD (variable frequency drive), DC speed regulator, temperature control instrument, and data acquisition module, they can be connected to HMI products to realize the human-computer interaction function.


Figure 1: ABB HMI screen

Q2: What is the difference between HMI and “touch screen”?

Strictly speaking, there is an essential difference between them. Because “touch screen” is only the hardware part that may be used in HMI products, which is an input device installed in the front of the display screen to replace some functions of mouse and keyboard. HMI products are a type of human - machine interaction device that includes hardware and software. In the industry, it is not scientific that people often call the HMI products with touch input function “touch screen”.

Fingers touching the phone on the touch screen

Figure 2: Touch screen

Q3: Is there operating system in HMI products?

HMI products have a system software component. The system software runs in the HMI processor, supporting multitasking. The processor needs a small management system software to run. In the high-performance HMI products based on the tablet computer, WinCE, Linux, and other general embedded operating systems are commonly used.

an embed HMI screen with Linux system

Figure 3: HMI with Linux system

Q4: What’s the difference between HMI and supervisory control and data acquisition (SCADA)?

HMI products are often called as "touch screen", contain HMI hardware and corresponding special SCADA software. In general, HMI hardware of different manufacturers use different SCADA software, and the main type of equipment connected is PLC.

SCADA software is a general tool software running on the PC hardware platform and Windows operating system, and it can also constitute HMI products together with PC or Industrial computer.

General SCADA software supports different types of equipment, including PLC, PC board cards, instruments, VFD, modules. Moreover, due to the strong performance of the PC hardware platform (mainly reflected in the speed and storage capacity), the SCADA software has many strong functions, which are suitable for large monitoring systems.

An SCADA software applied in industry

Figure 4: SCADA software

Q5: Can the device with communication function be connected to the HMI product?

It’s true normally. Because the universal HMI products provide a large number of commonly used device communication drivers to choose. Generally, the communication connection between HMI and the device can be completed as long as the communication driver corresponding to the connected device is selected in the SCADA software of the HMI products.

If there is no communication driver to be connected with the device in the SCADA software of the HMI product, the user can inform the HMI product manufacturer of the communication port type and protocol content of the device to be connected, and ask the manufacturer to compile the communication driver of the device.

Power: 24VDC,0.5A Fuse: 1.6A/250V 3.6*10mm

Figure 5: ABB HMI CP420B

Q6: Is HMI connected to devices only by standard serial communication interface ?

Most of the time. With the development of computer technology and digital circuit technology, the interface capability of HMI products is getting stronger and stronger. In addition to the traditional serial (RS232, RS422/RS485) communication interfaces, some HMI products with data interfaces such as network interface, parallel interface, and USB interface which can be connected to industrial control devices with the same interfaces to realize human-machine interaction of devices.

RS232 serial communication interface

Figure 6: Serial communication interface RS232.

Q7: Can PC with touch screen communicate directly with PLC to complete HMI function?

Sure. It is of importance that the corresponding HMI software should be compiled to make the PC a real HMI product.

HP Pavilion all-in-one PC

Figure 7: Touch screen computer

Q8: What is the trend of HMI?

As the development of digital circuit technology and computer technology, the functional gradation of future HMI products will be less and less necessary, and the functions of HMI will be more and more abundant. The screen of HMI products which is more than 5.7 inches will be all color display, whose service life will be longer.

Due to the reduced cost of computer hardware, tablet PC will be taken as the high-end products of HMI hardware. It’s because such products have great advantages in processor speed, storage capacity, types and quantity of communication interfaces, networking ability and software resource sharing, which is the development direction of HMI products in the future.

Of course, functions of small-sized HMI products with display size less than 5.7 inches are further enhanced (such as adding IO functions), as well as their size and price, so that they will be widely used in HMI applications of small mechanical devices.

CP620 Control Panel 4.3 TFT touch screen, 64 K colors, 480 x 272 pixel, PB610 runtime license

Figure 8: ABB HMI CP620

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