Background of HART
In the 80s the company Rosemount developed the first HART (Highway Addressable Remote Transducer). In 1989 the HART standard of the HART Communication Foundation (HCF) was introduced and it has been a part of the fieldbus standard IEC 61158 since 2007.
The fieldbus HART is now a fieldbus mostly oriented to the needs of the process industry. HART defines the communication protocol between multiple intelligent digital field devices and a control system. It is based on the conventional analog data technology 4…20 mA. This allows the use of existing wiring of legacy systems.
With the use of the FSK standard (Frequency Shift Keying) according to the Bell 202 4…20 mA Data transfer is overlaid by a digital signal.
The low-frequency analog signal is superimposed by a high-frequency vibration (+/- 0.5 mA). A digital 1 is represented by the frequency 1.2 kHz and a 0 by 2,2kHz. The data transmission via the HART bus is 1,2kBit/s.
By this overlay, a two-way communication can proceed with the field. This is used for additional extraction of data.
HART specifies the protocol layers 1 (Physical Layer), 2 (Data Link Layer) and 7 (Application Layer) in the OSI model and allows the transfer of process and diagnostics information as well as control signals between field devices and control system.
The communication of the device is performed by a master/slave protocol. This means that the slave (the intelligent field device) only returns information to the master (the host) when it is prompted.
Furthermore, an additional second master will be integrated, such as a mobile device. The data transfer is not disturbed between the slave and the primary master.
Benefits of HART
- simultaneous operation of existing, older and analog 4…20 mA and new digital systems
- mobile test equipment, calibration equipment and laptops for fast and easy analysis of field devices
- easy handling of the functional testing of field devices, diagnosis, and calibration
- increased plant availability through early detection of interfering signals
- reduction of maintenance costs by fast remote diagnostics
WirelessHART provides an overview of previously unused data from the field device. Thus, a collection of new measures is possible – and all this without wiring.
In 2007, the new standard was first introduced and published by the HCF. In order to avoid spurious signals and yet to ensure the safety, WirelessHART provides a lot of features.
The radio transmission corresponds to the IEEE standard 802.14.4-2006 which avoids a disturbance by channel jumps. Also a data encryption according to 128-bit AES industry standards is provided so that the data transfer and the commissioning of the field devices cannot be changed without authorization.
The HART-IP technology enables access to data over the Ethernet. Thus worldwide remote access on the device level would be possible, as well as an intelligent device management via Ethernet or Wi-Fi.
The Thorsis Technologies GmbH offers a wide range of communication solutions to integrate HART in the process and automation industry.
HART USB Interfaces
Commissioning using the HART USB Adapter
The commissioning of HART devices is easier than ever by using our HART-USB adapters. The affordable USB devices can easily be integrated into common configuration software via a virtual COM port.
The isNet Lite is an Ethernet or Modbus gateway, the isNet PNGate a PROFINET gateway in a compact modular housing. It can be used for multiple purposes of remote monitoring and control. The isNet Lite is used as a head station and also coordinates the connected fieldbus modules. Up to five different fieldbus-specific modules can be connected, the modules can be combined freely.
With the isNet H@rt modules, the head station isNet Lite can be expanded as HART Ethernet Gateway. The Ethernet Gateway represents a modern alternative to HART multiplexers because it allows direct connection to the existing data network of the plant. Because each channel has its own modem, the very low data transfer rates at multiplexers can be avoided.
The isNet H@rt Module is available as 4-channel version (single width) and as 8 – channel version (double width). In addition to the properties of isNet H@rt, the isNet H@rt+AI offers its own 24V-supply of the HART-Slaves including fuse and the possibility to transfer analog data. Up to five modules can be connected to the isNet Lite simultaneously so that a maximum of 40 HART channels can be managed. Each channel is electrically isolated from the network. Connection to the HART network is carried out by 8 screw terminals.
The modules can be used with Thorsis Technologies’ isHRT CommDTM. This way, an integration of the gateway in any FDT frame application is possible. For integration into Modbus or PROFIBUS a GSDML editor is available. To integrate the isNet H@rt into existing applications that are based on the use of multiplexer architectures, a virtual Com-Port solution was implemented.