Answer:
1.two-way communication:
using analog signal only transmit information, either from the device to the host ( input ), either from the host to the device ( output ). While using HART digital communication signal can be two-way transmission of digital information. It breaks through the traditional instruments can only be received from the host control signal way -- such as the valve control, can also refer to the information in the state of host transfer valve. Similarly, only to send to the host process variable transmitter now can also receive information such as configuration settings.

2.new types of information:
The traditional analog and discrete device only in single process variables to communication -- so it is very hard to find a convenient way to determine the transmitted information is valid. Using HART, you can not only acquire the process variable, can alsoreceive other types of information. Each HART device includes35-40standard information. For example:
(1)Device status &diagnosis and alarm
(2)Process variable &units
(3)Loop current &percentage range
(4)Manufacturers & equipment labels
Other information may also include: host in digital form to query the HART equipment, and inform you that your device settings are correct, whether it is normal operation. This function allows you to remove most of the daily inspection work, and help you in the fault cause major problems before the discovery process fault.

3.multivariable instrument:
Digital communication mode, a pair of cables can handle multiple variables. For example, a transmitter can handle multiple sensor input. For you cannot use the HART digital information to the host system, from multivariate instrument information usually consists of tri-loop first treatment, it will be converted into digital information group 4-20mA signal, then separate from the terminal is transmitted to the host.

4.not subject to supplier:
Using HART, you will not be subject to a particular supplier or local" standard". This is because the HART technology does not belong to a company, also do not suffer a country or a standard entity unit control. In fact, the technique consists of unconstrained non-profit units HART communication foundation management.

5.Multi channel supply:
On the process of processing industry, HART is the world's most widely used protocol. You can get almost 600from different suppliers based on HART technology products. Product variety complete means that HART products almost can meet all the process application occasions, and you can also see from multiple dealers products to choose the most suitable one.

6.Interoperability:
Complete interoperability means either that supplier's HART compatible products and the main system can work together. As with the HART equipment to achieve compatibility, some main system uses a unified representation of the instruction. Further, the system uses the device description to understand all of the HART information. If not from the HART equipment digital information system, but also through 4-20mA analog signal to realize the control of interoperability.

Answer:
HART (" highway addressable remote transducer" ) communication protocol, for industrial process measurement and control application and design. We will refer to as hybrid protocol because it is the will of analog and digital communication integration. It supports both 4-20mA analog signal to the single variable communication, can also be additional information in digital signal mode for communication. Digital information with low level modulation modes of loading in the standard 4-20mA current loop. Due to the adoption of the standard can be removed from the analog signal filtering technology, the digital signal and does not affect the simulation quantity signal readout. To send the superposition of the digital information is the important function of HART.