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Ultrasonic Level Sensor

 Ultrasonic Level Transmitter

The Ultrasonic sensor are also used in industrial applications to measure the level of liquids, slurries and solid.

The Ultrasonic level transmitter operates on the basic principle of using sound or acoustic  waves to determine liquid, solid or slurries level.

These devices measure the distance from a reference point in the vessel or tank to the level interface, using ultrasonic waves.

Frequency range of ultrasonic level sensor

Ultrasonic level transmitter measures actual distance, by issuing an ultrasonic pulse of ranging in the freaquency of 40 kHz to 70 k Hz.

The lower frequency of ultrasonic pulses can use to measure long range.

Mostly used frequency is 58 k Hz , at this frequency the resolution is  1 cm and sensing range of ultrasonic level sensor will be 11 meter. 

Working principle of ultrasonic level transmitter

 Ultrasonic level transmitter’s measure actual distance by issuing an ultrasonic pulse and measuring the time required for the reflected echo to be received back to the instrument.

Ultrasonic Level Transmitters consist of two elements; 

1) A high efficiency transducer 

 2) An associated electronic transceiver. 

Together, they operate to determine the time for a transmitted ultrasonic pulse and its reflected echo to make a complete return trip between the non-contacting transducer and the sensed material level. 

Transducer is installed at top-of-tank, this transducer directs waves downward in bursts onto the surface of the material whose level is to be measured. A piezoelectric crystal inside the transducer converts electrical pulses into sound energy that travels in the form of a wave at the established frequency and at a constant speed in a given medium. 

Echoes of these waves return to the receiver and time if flight is proportional to the level of. the medium.  



Dead band of ultrasonic level

Dead band (minimum measuring distance (X ): ) is a feature common of all ultrasonic level meters. 

This is a short range in front of the sensor within which the ultrasonic device cannot measure the level.

Maximum measuring distance (X ): 

The longest range under ideal condition within which the device can be  measured the level, no measurement ofof level is possible beyond the dead band and the maximum measuring distance.

Ultrasonic level sensors Applications

 These transmitter are non contact level measurement devices . These are used in applications when it is not acceptable for the level measuring instrument to come into direct  contact with the process material.

In addition to standard level or volume measurement, ultrasonic kevel trar can monitor open channel flow.

Ultrasonic Level measurement determine the actual volumetric throughput in lift stations.

Ultrasonic level transmitters are also used to measure differential level. 

We can use ultrasonic level transmitter for on off control of the pumps.

Ultrasonic sensor can also used to detect human presence.

Ultrasonic method can be effectively used for measurement of liquid level in a sealed tank. 

An ultrasonic transmitter/receiver pair is mounted at the top of the tank. Ultrasonic wave can pass through the liquid, but gets reflected at the liquid-air interface. The time taken to receive the pulse is measured, that can be related with the liquid level, it is directly proportional to the level. 

For accurate measurement, variation of speed of sound with the liquid density, temperature and pressure should be properly compensated for accurate result of level measurement.

Limitation of ultrasonic sensor

Not appropriate for non reflection liquids.

Ultrasonic level sensor may lead error in case of agitated liquids.
Ultrasonic Level measurement need a pressure limit in vessel less than 0.5 bar.


Excess exposure to ultrasonic more than 120 dB may affect heraing of human being.and excess than this  155dB may cause death.

How accurate are ultrasonic level sensors

Ultrasonic level transmitter have a resolution up to 0.09mm.

reliability of the ultrasonic level sensors is more than 0.5%.

Typical accuracy of ultrasonic sensor is better than 1 % of the range.




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