Which statement describes the encoding of data by 1200 Hz and 2200 Hz in HART?

Which statement describes the encoding of data by 1200 Hz and 2200 Hz in HART?

• A. They alternate to provide clock synchronization only
• B. They are used to represent voltages in the loop
• C. They encode binary values where 1200 Hz = 1 and 2200 Hz = 0
• D. They indicate start and stop bits

Answer: (C)

In HART, the digital data on the 4–20 mA loop is sent using frequency shift keying. Two distinct audio frequencies are used to represent binary values: 1200 Hz and 2200 Hz. The receiver identifies which frequency is present during each bit interval and converts that to a 1 or a 0. The specific mapping is that 1200 Hz encodes a binary 1, while 2200 Hz encodes a binary 0. This arrangement provides clear separation between bits, allowing reliable detection while the analog loop signal remains superimposed. It’s not about clock synchronization or voltages in the loop, but about representing data bits with two distinct tones.

In HART, the digital data on the 4–20 mA loop is sent using frequency shift keying. Two distinct audio frequencies are used to represent binary values: 1200 Hz and 2200 Hz. The receiver identifies which frequency is present during each bit interval and converts that to a 1 or a 0. The specific mapping is that 1200 Hz encodes a binary 1, while 2200 Hz encodes a binary 0. This arrangement provides clear separation between bits, allowing reliable detection while the analog loop signal remains superimposed. It’s not about clock synchronization or voltages in the loop, but about representing data bits with two distinct tones.