How does ultrasonic level measurement work?

Ultrasonic level sensors emit high-frequency sound pulses (typically 20-200 kHz) toward the liquid surface and measure the time for the echo to return. Level is calculated from distance = (speed of sound x time) / 2. These non-contact sensors are suitable for corrosive liquids and solids, unaffected by density or dielectric changes, but can be affected by foam, vapor, and temperature variations that change sound velocity.