Which statement correctly defines tone transmission in measurement signaling?

• A. A pure audible tone whose duration represents a measured value.
• B. A digital packet containing time-stamped data.
• C. A continuous stream of binary bits conveying the measurement.
• D. A radio frequency carrier with amplitude encoding the value.

Answer: (B)

Tone transmission in measurement signaling focuses on delivering data as structured digital messages rather than just analog tones. In practice, this means information is carried as digital packets that include the measurement value along with a timestamp, so the receiver knows exactly when the data were captured. This time-stamped packet approach supports synchronization, data integrity, and traceability over the loop, which is essential in systems like HART where a digital layer rides on top of the analog current signal. An audible tone whose duration encodes the value would be unreliable for precise measurement and highly sensitive to timing drift. A continuous stream of binary bits lacks the framing and timing context that packets provide, making interpretation more prone to errors. A radio frequency carrier with amplitude encoding is an analog modulation method, not a discrete, time-stamped digital packet sent on the loop. Therefore, a digital packet containing time-stamped data best defines tone transmission in measurement signaling.