HART is an over-extension bus standard proposed by Emerson. He mainly superimposes digital signals on the 4~20 mA current signal. The physical layer uses BELL202 frequency shift keying technology to realize the functions of some smart meters, but this protocol It's not a truly open standard. To join his foundation, you can get an agreement and join the foundation to get a part of the cost. The technology is mainly monopolized by several large foreign companies. In the past two years, there have been companies in China, but they have not yet reached the level of foreign companies. A large number of smart meters now come with HART round cards, all with HART communication. However, from the domestic point of view, it has not really utilized this part of the function. At most, it only uses the handheld device to parameterize it. It does not play the function that HART smart meter should have. There is no network for device monitoring. In the long run, due to the low HART communication rate and the difficulty of networking, the purchase volume of HART instruments will decline, but since HART meters have a history of more than ten years, the number of installed devices is very large, for some system integrators. There is still a lot of space available.
Fieldbus technology is one of the hotspots of technology development in the field of automation today. It is known as the computer LAN in the field of automation. Its appearance marks the beginning of a new era of automation control technology. The field bus is a network that connects digitally, serially, and multi-station communication devices that are placed at the control site with control devices that are placed in the control room. Its key symbol is to support two-way, multi-node, bus-based all-digital communication. In recent years, fieldbus technology has become a hotspot in the development of automation and instrumentation in the world. Its emergence is a revolutionary change in the structure of traditional control systems. It is the automation, digitization, informationization, networking and decentralization of automatic control systems. The direction is moving forward to form a new type of network-integrated fully distributed control system---Fieldbus Control System (FCS). However, the various standards of the fieldbus exist in parallel and have their own areas of existence. They have not yet formed a truly unified standard. The key is not to see when a unified standard can be formed, and the technology is not mature enough. In addition, the types of instruments on the field bus are still relatively small, and the price is also high. From the perspective of the end user, most of them are still in a wait-and-see state. They all want to wait until the technology is mature, and now it is implemented less.
Both HART and fieldbus technologies enable remote access to the status and parameters of field devices. At the same time, both technologies support a networked way of connecting multiple devices on a single bus. Both HART and fieldbus use device descriptions to enable interoperability and comprehensive use of devices. Therefore, there are certain similarities between them.
There are four differences between them:
1) The fieldbus uses true all-digital communication, and HART is superimposed on the original 4~20mA analog signal by FSK, so it can be directly connected to the existing DCS system without reconfiguration;
2) Multi-point connection is used for fieldbus. HART protocol generally adopts multi-point connection mode only when it is used for monitoring.
3) In the control system composed of field bus, devices can communicate directly without intervention by the host;
4) Fieldbus devices provide more diagnostic information than HART devices.
Therefore, the fieldbus device is suitable for high-speed network control systems, and the superiority of HART devices is reflected in the compatibility with existing analog systems.