The on‑board microprocessor simultaneously fires an electronic pulse and starts a timer. The transducer converts this electronic pulse to an acoustic pulse, which is directed toward the surface of the material being measured. When the acoustic pulse contacts the surface of the material, energy is reflected back to the transducer, which converts the energy back to an electronic pulse. This pulse is sent back to the microprocessor, which stops the timer and determines the time‑of‑flight of the signal. By combining the speed of sound through air and the time‑of‑flight of the pulse, the microprocessor accurately determines the level of the product. Powerful software removes false echoes from the signal and electronic filters remove ambient noise.

Ultrasonic measurement

Using a time‑of‑flight calculation, and knowing the height of the vessel, the LST accurately measures the distance to the target surface using the equation below:

Level = height - speed of sound x time-of-flight 
                        2

Temperature changes the speed of sound, making accurate measurement more challenging. All LST instruments measure and compensate for temperature changes in the background, ensuring accurate measurement over a wide range of ambient conditions.