HART is an acronym for Highway Addressable Remote Transducer. In very simple terms, HART devices are ´smart´ process instruments, and most 4-à20 mA devices are HART capable. The HART protocol uses Bell 202 Frequency Shift Keying (FSK) to superimpose digital communication signals on top of the 4-20mA analog signal. It´s like Caller ID (digital data) on a telephone land line (analog signal). The 4-20mA signal communicates the primary measured value, while the digital signal contains information from the device including device status, diagnostics and additional measured or calculated values.
HART devices are rich in diagnostic data. Many devices are capable of monitoring the condition of the sensor or probe, which can be an early indicator of inaccurate measurements. It is also possible to detect a configuration error or operating mode which may lead to problems in the future. Most importantly, the availability of additional data can be used to determine the health of a large piece of equipment or the quality and efficiency of a process, avoiding unplanned maintenance in the future. Most HART devices are multivariable, meaning that they can provide multiple measurement values, although only the primary variable is represented by the 4-à20 mA signal while the other variables are only available as digital data.
HART IP provides another option to address the growing demand for Ethernet based communication. It is the same HART protocol adapted to an IP-based connection. HART IP enables software applications to gain direct access to information in devices such as WirelessHART gateways, multiplexers, remote I/O and other devices without having to convert to another protocol such as Modbus or OPC.
Users can benefit by using the existing Ethernet network in a facility to distribute the data to multiple departments and systems, as well as from the improved communication medium.
HART IP requires no special networking equipment, and is compatible with any standard Ethernet (IEEE 802.3) switches or media converters. It´s lightweight and ideal for use with wireless networks, including 802.11, LTE, and GPRS.
The global view
Standardised nearly 30 years ago, HART is the world´s most broadly supported protocol for the process industry. HART was originally developed as a way to make analog process measurement devices ´smarter´ by superimposing digital data on a 4-à20 mA signal loop; today, the standard continues to develop with the introduction of more ways to connect - including wireless and Ethernet. Moreover, backwards compatibility and manufacturer interoperability means there´s no danger of getting locked into vendor-specific or regional solutions. There are approximately 40 million HART devices installed worldwide. Only about 10 per cent of them are using their HART capabilities. By utilising the diagnostic data, operating expenditures can be reduced while increasing availability.
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