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).
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When to use Ultrasonic Sensors

Ultrasonic level sensors are ideal for continuous level measurement of liquids and solids in environments without gases or vapours such as CO2, CO, H2S, H2.

Propagation of Ultrasonic Sound Waves

  • Sounds waves are mechanical waves and require a medium to travel
  • Speed of ultrasonic sound wave is 343 m/s at 20°C to a target
  • The speed of sound through air depends on temperature (most significant factor), pressure and humidity
  • Material with a different density and speed of sound than air reflects ultrasonic waves

  • The reflection depends on the density of the material. As an example, high density material such as water gives good reflections while low density material such as foam gives poor reflection (permeable targets absorb more reflected ultrasonic energy)

Types of Ultrasonic Level Sensors

There are several types of non-contact ultrasonic level sensors available, each suited to different applications, environments or the material being measured.

View ABM Ultrasonic Level Sensors >
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