Fieldbus selection problem - Database & Sql Blog Articles

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Before specifically determining which fieldbus product to use, in general, the following aspects should be clarified:

1. The size of the scale, that is, how many nodes need to use the field bus to form a network.

The size of the scale has an impact on the choice of the field bus. For example, CAN can connect up to 110 devices, while the number of nodes in LONWORKS can reach 32,000, and the number of nodes in PROFIBUS is from tens to more than one hundred.

2. Environmental conditions: This includes the distance of the node distribution, the safety and explosion requirements of the site, and the electromagnetic environment.

The difference in environmental conditions has an impact on the choice of the field bus. First, the distance of the node distribution determines the length of the communication line. In this respect, the capacity of different buses is different, and the range of variation is tens of meters to 10 kilometers. The safety explosion-proof requirements on site are a very important indicator. According to the above analysis, except for the CAN bus, the other can meet the requirements of safety explosion-proof. According to the current development trend, it is best to use H1 of PROFIBUS-PA or FF. The advantages and disadvantages of the on-site electromagnetic environment determine the communication medium that constitutes the network. If the electromagnetic interference on the site is serious, it is best to use optical fiber as the transmission medium.

3. Transmission signal situation: This includes the transmission signal is analog or digital, the amount of information, the requirements for real-time. Different transmission signal conditions also impose different requirements on the field capability. If the analog and digital signals coexist, HART can be used. If the amount of information transmitted is particularly large, the real-time performance is not high, you can consider PROFIBUS-FMS; if it is information volume Large, real-time high, you can consider the choice of PROFIBUS-FMS and PROFIBUS-DP system.

4. Field equipment situation: This refers to the technical transformation of the old equipment, or the use of new smart meters that meet the requirements of the fieldbus. This situation exists in many units in China. Since many of the instruments used in the original are Type II or Type III watches, and the current use is better, but it is hoped to use advanced fieldbus technology to improve the comprehensive automation level of production. This is actually a proposal to establish a fieldbus network based on the full use of the original old equipment. Fortunately, the remote intelligent I/O provided by the market can meet this requirement. For example, the domestic Beijing Zhongji Pufa Industry and Trade Development Co., Ltd. can produce this kind of product. Through this I/O, the traditional instrument can be simulated. The 20 mA or 0-5 volt signal is converted into a fieldbus compatible communication signal to enable connection and communication with the fieldbus network. This kind of scheme is a desirable way to carry out technological transformation of some old enterprises that are not financially sufficient. In short, as a user, we always want to choose the product with the best performance-price ratio. However, because the user's own needs vary widely, often a kind of on-site product is difficult to meet the needs of all aspects, so in the actual selection, we can use the gateway technology. , integrate different fieldbuses to meet your own requirements.

In addition, if there are several products that meet your own requirements and the performance price ratio is similar, the factor to be considered should be the service. If there are many users, the service is good (including installation, Training, maintenance, etc., should consider giving priority to this product. According to the current situation, PROFIBUS and FF have advantages in this respect.