How to choose PLC products

In modern industrial production equipment, there are a large number of digital and analog control devices, such as the start and stop of motors, the opening and closing of solenoid valves, the counting of products, the setting and control of temperature, pressure, and flow, etc. For these automatic control problems in industrial sites, using programmable logic controllers (PLCs) to solve automatic control problems has become one of the most effective tools.

Hardware selection: There are many PLC products on the market, including domestic brands, foreign brands such as Japan's OMRON, MITSUBISHI, FUJJ, anasonic, Germany's SIEMENS, South Korea's LG, etc. In recent years, the price of PLC products has dropped significantly, and its cost performance is getting higher and higher, which is an important reason why many technicians choose PLC.

So, how to choose PLC products?

1. System scale First, determine whether the system uses a single PLC or a PLC network, and then calculate the number of PLC input and output points. When purchasing a PLC, leave a certain margin (10%) based on the actual number of points required.

2. Determine the load type. According to whether the load at the PLC output terminal is DC or AC, whether it is a large current or a small current, and the frequency of the PLC output point action, determine whether the output terminal uses a relay output, a transistor output, or a thyristor output. It is very important to use different output methods for different loads to ensure the stable operation of the system.

3. Storage capacity and speed Although the PLC products of foreign manufacturers are generally the same, there are certain differences. At present, no completely compatible products have been found between companies. The development software of each company is different, and the storage capacity of the user program and the execution speed of the instruction are two important indicators. Generally, the larger the storage capacity and the faster the speed of the PLC, the higher the price, but the PLC product should be reasonably selected according to the size of the system.

4. Selection of programmer PLC programming can be done in three ways:

It is programmed with a general handheld programmer, which can only program with the statements in the statement table specified by the merchant. This method is inefficient, but it is more suitable for products with small system capacity and small usage, and it is small in size, easy to debug on site, and has a low cost.

It is programmed with a graphic programmer, which uses ladder diagram programming, which is convenient and intuitive. General electrical personnel can use it freely in a short period of time, but the programmer is relatively expensive.

It is programming with an IBM personal computer plus a PLC software package. This method is the most efficient method, but most companies' PLC development software packages are expensive, and this method is not easy to debug on site.

Therefore, PLC products should be selected reasonably based on the size and difficulty of the system, the length of the development cycle and the financial situation.

5. Try to choose products from large companies whose quality is guaranteed, and they have good technical support and generally good after-sales service, which is also beneficial to your product expansion and software upgrades.