Here are some good ways to understand HART communication or HART protocol?
What Is Hart?
The HART Communication Protocol (HART = Highway Addressable Remote Transducer). HART is a master-slave communication protocol, which means that during normal operation, each slave (field device) communication is initiated by a master communication device. Two masters can connect to each HART loop. The primary master is generally a distributed control system (DCS), a programmable logic controller (PLC), or a personal computer(PC). These secondary master can be a handheld terminal or another PC. Slave devices include transmitters, actuators, and controllers that respond to commands from the primary or secondary master.
Actually, it’s not just a standard, but it’s a global standard for sending and receiving digital information along analog wires between smart devices and host systems.
Why Use Hart Technology?
HART technology has proved to be easy to use and very reliable. The HART protocol is a powerful communication technology used to exploit the full potential of digital field devices. Preserving the traditional4–20 mA signal, the HART protocol extends system capabilities for two-way digital communication with smart field instruments. The HART protocol offers the best solution for smart field device communications and has the widest base of support of any field device protocol worldwide. More instruments are available with the HART protocol than any other digital communications technology. Almost any process application can be addressed by one of the products offered by HART instrument suppliers.
Unlike other digital communication technologies, the HART protocol provides a unique communication solution that is backward compatible with the installed base of instrumentation in use today. This backward compatibility ensures that investments in existing cabling and current control strategies will remain secure well into the future.
Benefits outlined in this section include:
• Improved plant operations
• Operational flexibility
• Instrumentation investment protection
• Digital communication
What Does Hart Communication do?
The hart protocol permits the process variable to continue to be transmitted by the 4-20 mA analog signal and additional information pertaining to other variables, parameters, device configuration, calibration, and device diagnostics to be transmitted digitally at the same time. Thus a wealth of additional information related to plant operation is available to central control or monitoring systems through HART communication.
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What Is A Device Description?
Some HART host applications use device descriptions (DD) to obtain information about the variables and functions contained in a HART field device. The DD includes all the information that a host application needs to communicate completely with the field device.
The HART device description language (DDL) is used to write the DD, which combines all the information needed by the host application into a single structured file. The DD identifies which common practice commands are compatible, as well as the format and structure of all device-specific commands .A.
DD for a HART field device is roughly equivalent to a printer driver for a computer. DDs eliminate the need for host providers to develop and support custom interfaces and controllers. A DD provides an image of all the parameters and functions of a device in a standardized language.
HART providers have the option to supply a DD for their HART field product. If you choose to provide one, the DD will provide information so that a DD-enabled host application can read and write data according to the procedures of each device. The DD source files for HART devices look like files written in the C programming language. The DD files are sent to the HCF for registration in the HCF DD Library.
Quality controls are performed on each DD sent to ensure compliance with the specifications, to verify that there are no conflicts with DD already registered, and to verify the operation with standard HART hosts.
The HCF DD Library is the central location for administration and distribution of all HART DDs to facilitate use in host applications such as PCs and handhelds. Additional information, not provided by the DD, may be required by some host applications for the screen format and other uses.
How Does A Hart Assist Commissioning And Configuration?
HART technology has significantly reduced the time required to launch a network (loop). For example. the devices can be verified more quickly since the specific information of the device and the application is loaded into instruments that can be quickly verified by the host control system. Commissioning is further simplified by connecting a PC configuration to each HART communication loop online, either through the control system or a multiplexing I / O system.
This eliminates the need to move the configuration device from one termination point to the next while the devices are running on the network. The main PC configuration applications also include a loop test function that guarantees the proper connections and installed record keeping functions for long-term documentation and maintenance.
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