HART, which stands for Highway Addressable Remote Transducer, is a communication protocol commonly used in process automation for communication with field devices. It allows digital communication between smart field instruments and a control system, providing additional information beyond traditional 4-20 mA analog signals.
Key features and characteristics of HART protocol:
1. Hybrid Communication:
HART is a hybrid communication protocol, meaning that it supports both analog and digital communication. While the primary analog 4-20 mA signal is used for transmitting the primary process variable, HART enables simultaneous digital communication to exchange additional information.
2. Bi-Directional Communication:
HART allows bi-directional communication between a smart field device and the control system. This enables the control system to query and configure the device in addition to receiving process variable information.
3. Two-Wire Communication:
HART operates over the same two-wire loop used for the analog 4-20 mA signal. This allows existing wiring infrastructure to be used for implementing HART communication without additional cabling.
4. Master-Slave Architecture:
In HART communication, the field device (such as a transmitter or actuator) acts as the slave, while the control system or HART communicator serves as the master. The master initiates communication and requests information from the field device.
5. Communication Speed:
HART communication typically occurs at a low speed, often in the range of 1200 bps (bits per second) or 9600 bps. This relatively low speed is sufficient for transmitting additional digital information without interfering with the analog signal.
6. Superimposed Digital Signal:
The digital HART signal is superimposed on the analog 4-20 mA signal. This allows devices that support only the analog signal to function properly, while devices with HART capabilities can utilize the additional digital communication.
7. Device Identification and Addressing:
Each HART device has a unique address, allowing the control system to address and communicate with specific field devices on the loop. This enables the control system to interact with multiple devices on the same loop.
8. Parameter Configuration:
HART allows for the configuration of various parameters in smart field devices. This includes setting calibration values, configuring measurement ranges, and adjusting device-specific parameters.
9. Additional Information:
HART provides a means to transmit additional information beyond the primary process variable. This can include diagnostic information, device status, and secondary measurements, enhancing the capabilities of smart field instruments.
10. Compatibility:
HART is widely adopted in the process industry, and many field devices, such as pressure transmitters, temperature sensors, and control valves, support the HART protocol. This ensures interoperability between devices from different manufacturers.
HART is commonly used in industries such as oil and gas, chemical, and manufacturing, where accurate and efficient communication with field devices is crucial for process control and monitoring. The protocol’s ability to provide additional information without disrupting existing analog signals has contributed to its widespread adoption in industrial automation.
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