For the development of an automated system, there are many development platforms that can be used. Common ideas include the following: 1. A control system with an embedded programmable chip such as a single-chip computer, DSP, etc. as the core. 2. A control system with a capture card as the core. 3. Control system with PLC as the core. Below, we will compare the pros and cons of each program, so as to provide a reference for us to design an automated system in the future.
1. Microprocessor-based control system
The hardware of the control system with microprocessor as the core mainly includes the design of signal conditioning circuit, converter, processor circuit, communication interface circuit and power supply circuit. The software mainly includes processor embedded programs, communication protocols, and human-machine interface programs (in the case of a host computer). The following figure shows the general structure of the control system.
For this solution, it is the lowest and most complex solution. We first need to design a hardware circuit and go through the process of making a model. This process takes as little as ten days and a half months, and it takes longer to redo if you encounter problems. Next, you need to write a program. The program is divided into an embedded program and a host computer program. The length of time to write a program is related to system requirements and programmer experience. Embedded programs are usually written in C language. There are many programming languages available for host computer programs. Popular ones include C++, Labview, LabWindows, VB, etc. Labview is relatively simple. After the program is written, joint debugging of software and hardware and joint debugging of the host computer and the single-chip program are also required. These tasks are both time-consuming and laborious. Nowadays, the labor cost is getting bigger and bigger, the cost of the whole scheme can be said to be spent on human resources, and the development of the system also needs a long period.
2. The control system with acquisition card as the core
This solution reduces the design workload. The acquisition card is a hardware that contains A/D, D/A conversion circuits and communication interfaces. At the same time, many acquisition cards also have PWM, IO interface and other functions, which can be adapted to a wider range of applications. If the sensor selection and the acquisition card selection are appropriate, no signal conditioning circuit is even needed, which greatly saves the time of hardware design and debugging.
At the same time, the acquisition card has an embedded program developed and can be used by connecting to a power source. Therefore, the use of capture cards also reduces the task of program development. Each function software attached to the capture card has a program interface, which can quickly call and build a personalized application. Programmers only need to add example programs to their own programs to quickly develop their own man-machine interface programs, which can reduce debugging work and development time.
In short, the use of acquisition cards as the core simplifies hardware design and software writing compared to the single-chip solution. Of course, in the past, if the acquisition card solution was used, the cost of mass production was too high. For example, with NI and Advantech data acquisition cards, the unit price is basically 10,000 yuan. For most users who value cost, they will still choose the previous solution. , Develop your own collection system. However, the price of the domestically produced capture card is already very low. The price of the general-purpose capture card is only a few hundred yuan. Compared with the relatively large labor cost, the advantage of using a capture card to develop a control system is obvious, which helps us to develop and control quickly. Cost, even if the user develops the acquisition system, the cost of production debugging and management is difficult to lower than the cost of directly using the existing data acquisition card.
3. PLC as the core control system
PLC is mainly used in control systems with particularly high stability requirements and low speed, and the application scenarios are very limited. In addition, the price of PLC is higher than the previous two programs, so it is not recommended to use this program except in special fields.
Finally, I will introduce two cost-effective capture cards:
HK-USB-V12 data acquisition card (purchase link)
AD: 12-bit precision, single channel 100KHz sampling rate, 16 channels, multi-range optional
IO: 16 channels, 5V level
DA: 12-bit precision, 2 channels, 10V range
Additional functions: PWM measurement, PWM output, 32-bit counter
HK-USB-V53 data acquisition card (purchase link)
AD: 16-bit precision, 200KHz sampling rate, 4-channel simultaneous acquisition, multi-range optional
IO: 32 channels, 5V level
DA: 12-bit precision, 2 channels, 10V range
Additional functions: 2-channel PWM measurement, 2-channel PWM output