What is an Ultrasonic Level Sensor?

What is an Ultrasonic Level Sensor?

An ultrasonic level sensor is a device that uses sound waves to measure the level of a substance, such as a liquid or solid material, in a tank, silo or bin. It is a continuous level measurement device that provides real-time, non-contact measurement.

Ultrasonic Level Sensor Working Principle

The basic working principle involves transmitting a short pulse of ultrasonic sound from the sensor and measuring the time it takes for the sound wave to travel to the target and back. The time-of-flight is then used to calculate the distance.

Here is the step-by-step process:

  • A pulse transmitter stimulates an ultrasonic air transducer (a device that converts electrical energy into mechanical vibrations and vice versa), generating a sound wave.
  • The wave propagates through the air to the surface of the target and then reflects back towards the sensor.
  • The reflected wave is received by the same transducer in the receiver mode and converted to an electrical signal.
  • The electrical signal is amplified and processed to find the reflected echo.
  • The sensor captures the difference in time between the emitted and received echo.
  • Distance to the target is calculated using the speed of sound, a known variable, and the round-trip time as shown in the following equation:
      • Distance = Time x Speed / 2
      • Where division by two is required as time measurement is round-trip (to the target and back)
  • The calculated distance is converted linearly to 4 mA to 20 mA current. Optionally, information can be sent via RS232 or RS485 to a PC for processing (i.e. diagnostics, programmable set-up and data logging).
ultrasonic level sensor working principle, what is an ultrasonic level sensor

Propagation of Ultrasonic Sound Waves

  • Speed of sound is 343 m/s at 20°C (68°F)
  • The speed of sound through air depends on temperature (the most significant factor), pressure and humidity
  • Material with a different density and speed of sound than air reflects ultrasonic waves
  • Hard surface, high-density materials give good reflections, such as water
  • Soft surface, low-density materials give poor reflections, such as foam (permeable targets absorb more reflected ultrasonic energy)

Learn more about ABM’s non-contact ultrasonic level sensors here.

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