Which type of transmission is used in HART Protocol?
Which Type of Transmission is Used in the HART Protocol?
The HART (Highway Addressable Remote Transducer) protocol uses a Frequency Shift Keyed (FSK) transmission method to let digital signals work with the old 4–20 mA analog signal. This means that HART is a hybrid communication protocol that can send both analog and digital signals over the same two lines.
How FSK Transmission Works in HART
- The 4–20 mA analog signal still shows the main process variable, like flow, pressure, or temperature.
- At the same time, an FSK digital signal is added to the same loop without affecting the analog signal.
- FSK works by giving two different frequencies to digital bits:
1200 Hz = Logic “1”
2200 Hz = Logic “0”
- This communication has a bit rate of 1200 bits per second (bps), which is fast enough for configuration, diagnostics, and secondary variable data transfer. It also works with analog control systems.
Key Benefits of FSK in HART
- No interference – The digital signal rides on the analog loop without changing the 4–20 mA reading.
- Compatibility: It works perfectly with current analog instruments and adds smart digital features.
- Two-way communication lets you both monitor (device-to-host) and set up (host-to-device).
The HART protocol sends data over the 4–20 mA current loop using FSK transmission at 1200/2200 Hz and 1200 bps. This simple but effective technology makes it possible to send digital messages reliably without losing compatibility with older analog systems.