What are the modes of HART?
What are the Modes of HART?
The HART (Highway Addressable Remote Transducer) protocol is one of the most common ways for process industries to talk to one other. It combines the old 4–20 mA analog signal with a digital communication signal so that both control and diagnostics can be done via the same pair of wires. HART devices can work in two different ways, depending on the use:
1. Point-to-Point Mode (Analog/Digital Mode)
This is the most typical way for HART to work.
- A 4–20 mA loop connects the control system to one field device, like a transmitter.
- The analog signal (4–20 mA) shows the main process variable, like pressure, temperature, or flow.
- A digital HART signal is also added on top of this, conveying extra information like secondary variables, calibration data, or diagnostics.
- This mode lets you use old analog equipment while also giving you clever communication options.
2. Multi-Drop Mode
When more than one device has to use the same communication connection, this mode is employed.
- You can connect up to 15 HART devices on one pair of cables.
- There is a unique polling address (1–15) for each device.
- When in multi-drop mode, the analog loop current stays at 4 mA and all process data is sent digitally.
- This mode is very helpful for monitoring applications where a lot of sensors send data to a central controller.
HART’s point-to-point mode makes sure it works with traditional control systems, while its multi-drop mode makes digital networking more efficient. HART is a flexible protocol for both control and diagnostics because of these modes.