HART

How HART Works

Using the Bell 202 FSK (Frequency Shift Keying) standard, a digital signal is superimposed on the 4–20 mA data transmission.

The low-frequency analog signal is superimposed with a high-frequency oscillation (+/- 0.5 mA). A digital 1 is represented by a frequency of 1.2 kHz and a 0 by 2.2 kHz. Data transmission over the HART bus is 1.2 kbit/s.

This superimposition enables two-way communication with the field. This serves to obtain additional data.

HART specifies protocol layers 1 (Physical Layer), 2 (Data Link Layer), and 7 (Application Layer) in the OSI model and allows the transmission of process and diagnostic information as well as control signals between field devices and the control system.

Device communication is handled via a master/slave protocol. This means that the slave (the intelligent field device) only sends information to the master (the host) when requested to do so.

Furthermore, an additional second master can be integrated, such as a mobile device. This does not interfere with data transfer between the slave and the primary master.

Advantages of HART

• Simultaneous operation of existing, older, and analog 4–20 mA systems alongside new digital systems
• Mobile test devices, calibration devices, and laptops for quick and easy analysis of field devices
• Easy handling of field device functional testing, diagnostics, and calibration
• Increased plant availability through early detection of fault signals
• Reduced maintenance costs through rapid remote diagnostics

Additional Technologies

WirelessHART

WirelessHART provides access to previously unused data from field devices. This enables the acquisition of new measurement parameters—all without any wiring.

The new standard was first introduced in 2007 and published by the HCF. To prevent interference while still ensuring safety, WirelessHART offers a wide range of features.

The radio transmission complies with the IEEE 802.14.4-2006 standard, which prevents interference through channel hopping. Data encryption according to 128-bit AES industry standards is also provided to ensure that data transfer and the configuration of field devices cannot be altered without authorization.

HART-IP

HART-IP technology enables access to data via Ethernet. This allows for remote access to devices from anywhere in the world, as well as intelligent device management via Ethernet or Wi-Fi.

Thorsis Technologies offers a comprehensive range of communication solutions for integrating HART into the process and automation industries.