SLAAEH0 November   2023 AFE781H1 , AFE782H1 , AFE881H1 , AFE882H1 , DAC161P997 , DAC161S997 , DAC7750 , DAC7760 , DAC8740H , DAC8741H , DAC8742H , DAC8750 , DAC8760 , DAC8771 , DAC8775

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction to the HART Protocol
    1. 1.1 Different Forms of the HART Protocol
    2. 1.2 HART as an Enhancement to the 4-20 mA Loop
    3. 1.3 The HART FSK Signal
    4. 1.4 HART Configurations
    5. 1.5 HART Protocol Structure
      1. 1.5.1 HART Communication
      2. 1.5.2 HART Bytes
      3. 1.5.3 HART Data Frame Structure
        1. 1.5.3.1 HART Start Byte
        2. 1.5.3.2 HART Device Addressing
        3. 1.5.3.3 HART Commands
  5. 2HART Protocol and Test Specifications
    1. 2.1 The OSI Protocol Model
    2. 2.2 HART Protocol Specifications
    3. 2.3 HART Test Specifications
  6. 3TI HART Enabled Devices
    1. 3.1 TI DACs with HART Connections
    2. 3.2 TI HART Modems
  7. 4Conclusion
  8. 5References

1 Introduction to the HART Protocol

The Highway Addressable Remote Transducer (HART) protocol is a backward-compatible enhancement to 4-20 mA instrumentation that allows two-way communication with smart, microprocessor-based field devices.

For factory automation and control (FA&C) applications, 4-20 mA current loop communications are a common method to send data from a remote transmitter measuring a factory variable back to a host that receives and processes the data. The value of current is the primary variable sent by the remote transmitter. This primary variable represents some measure of temperature, flow, or pressure.

The HART signal is superimposed onto this 4-20 mA current loop and is modulated for two-way digital communications. The 4-20 mA loop is already a widely used standard in FA&C applications. Because this technology is backwards compatible and can be used with already-existing infrastructure means that HART is easy to adopt and cost effective.

HART is a command/response protocol where a host sends commands and a remote transmitter returns standardized responses. The data received by the commands can communicate device status and diagnostics. Data can also include the device measurement floating-point digital values, the engineering units of the primary variable, and other information about the remote transmitter.

The HART protocol can also be used for standardized operating procedures such as testing the current loop, range setting of the current loop, and calibration information from the transmitter. HART modifies the 4-20 mA system that sends only the primary variable as a current value and adds digital communication with more functionality.