What is HART Protocol - highway addressable remote transducer protocol for process automation

Summary

This session introduces the HART Protocol, a crucial smart instrumentation fieldbus protocol used in industrial automation. It highlights HART's hybrid analog and digital communication, which operates using Frequency Shift Keying (FSK) to transmit digital data over existing 4-20 mA analog lines. The video covers its cost-effectiveness, working modes (Point-to-Point and Multidrop), and the importance of a 250 Ohm resistor in the current loop. Additionally, it introduces the HART Communicator, a handheld device for field calibration and diagnostics. Viewers are encouraged to provide feedback and suggest topics for future sessions.

Takeaways

• 📡 HART (Highway Addressable Remote Transducer) protocol is a hybrid communication protocol that combines analog and digital signals.
• 💡 HART operates on a 4-20 mA current loop while superimposing digital information using Frequency Shift Keying (FSK).
• 🔧 HART Protocol was developed by Rosemount and is an open standard, making it widely used in industrial automation.
• ⚙️ The protocol uses two frequencies (1200 Hz and 2200 Hz) to represent digital bits 1 and 0, without distorting the 4-20 mA analog signal.
• 💲 A key advantage of HART is cost efficiency, as it uses existing 4-20 mA wiring for both analog signals and additional digital data.
• 🔌 HART supports two communication modes: Point-to-Point mode (with polling address 0) and Multidrop mode (for up to 64 devices).
• 📶 In Multidrop mode, each device is assigned a unique address, and communication happens at a 1200 baud rate in a poll/response system.
• 📱 A HART Communicator is a handheld device used to calibrate, read, and write to field devices in the system.
• ⚡ A 250-ohm resistor is commonly used in HART current loops to allow the FSK signal to be received, preventing filtering out by the power supply.
• 🔍 HART technology enables diagnostics, remote re-ranging, manual mode activation, and programming of field devices with identification data.

Q & A

What does HART stand for, and what is its purpose?

HART stands for Highway Addressable Remote Transducer. It is a communication protocol used in industrial automation to transmit both analog and digital data over the same 4-20 mA lines, allowing field instruments to communicate with PLCs and provide diagnostic information.

Who developed the HART protocol, and why has it become widely used?

The HART protocol was developed by Rosemount and has become popular because it is an open standard, meaning any manufacturer can use it. This has led to widespread adoption across manufacturers and extensive use in process automation.

How does HART Protocol differ from other fieldbus protocols?

Unlike purely digital fieldbus protocols, the HART protocol is a hybrid protocol that operates in a 4-20 mA analog format while superimposing digital signals via Frequency Shift Keying (FSK), allowing it to carry both analog and digital data simultaneously.

What technique does HART Protocol use to transmit digital data on an analog signal?

HART uses Frequency Shift Keying (FSK) to superimpose digital data onto the analog 4-20 mA signal. It uses 1200 Hz to represent a binary '1' and 2200 Hz to represent a binary '0', with each signal peaking at 1 mA.

How does HART Protocol ensure the analog 4-20 mA signal remains unaffected by digital communication?

The average value of the superimposed 1200 Hz and 2200 Hz FSK signals is zero, which ensures that the base 4-20 mA analog signal remains unaffected by the digital communication.

What is the advantage of using the HART Protocol in terms of infrastructure cost?

The HART Protocol allows digital data to be transmitted on the same two wires used for the 4-20 mA analog signal. This eliminates the need for additional wiring, saving installation costs while still adding digital capabilities for diagnostic and parameter information.

What are the two main operating modes of HART Protocol, and how do they differ?

HART operates in Point-to-Point mode and Multidrop mode. In Point-to-Point mode, the device sends both 4-20 mA signals and digital data, while in Multidrop mode, each device on the network is assigned a unique address and communicates only digitally, with a constant 4 mA signal.

What is a HART Communicator, and what are its primary functions?

A HART Communicator is a handheld device that acts as a second master in a HART system. It is used to read, write, range, and calibrate devices on the bus. Portable and battery-operated, it provides field technicians with the flexibility to perform diagnostics and adjustments directly on site.

Why is a resistor necessary in a HART current loop, and what is the typical range for this resistor?

A resistor, typically between 250 and 1100 Ohms, is necessary in a HART current loop to generate a readable voltage for FSK signals. This allows the HART communicator to receive data, as the resistor creates a detectable voltage when the 1 mA FSK signal passes through it.

How many devices can be connected in a Multidrop mode with the latest revision of HART, and how does polling work?

With HART revision 07, up to 64 devices can be connected in Multidrop mode. The master device polls each connected device individually in a poll/response format to gather the required information, allowing communication with each device one at a time.