Which measuring and transmitting level device works readily on a 4-20 mA system but needs a temperature correction?

Which measuring and transmitting level device works readily on a 4-20 mA system but needs a temperature correction?

• A. pressure activated
• B. sonic type
• C. float type
• D. magnetic type

Answer: (B)

Measuring devices that use sonic pulses rely on the speed of sound in air to convert how long a pulse takes to travel to the surface and back into a level distance. The speed of sound changes with temperature, so without correcting for temperature, the calculated level would be biased. Sonic level transmitters are well-suited to a 4-20 mA loop for transmitting the signal, but to stay accurate they require temperature correction to account for those speed-of-sound changes. Other types—pressure-based, float, or magnetic—are governed by principles that don’t depend on the speed of sound in air, so they don’t inherently need that same temperature correction in the same way.

Measuring devices that use sonic pulses rely on the speed of sound in air to convert how long a pulse takes to travel to the surface and back into a level distance. The speed of sound changes with temperature, so without correcting for temperature, the calculated level would be biased. Sonic level transmitters are well-suited to a 4-20 mA loop for transmitting the signal, but to stay accurate they require temperature correction to account for those speed-of-sound changes. Other types—pressure-based, float, or magnetic—are governed by principles that don’t depend on the speed of sound in air, so they don’t inherently need that same temperature correction in the same way.