Ultrasonic level measurement is a contactless principle and is most suitable for level measurements of hot, corrosive, and boiling liquids.

Ultrasonic level measurement provides a Continuous level measurement in liquids and solids with ultrasonic level sensors。 Non-contact, and maintenance-free level measurement of fluids, pastes, sludges, and powdery to coarse bulk materials. The measurement is unaffected by dielectric constant, density, or humidity. And also unaffected by build-up due to the self-cleaning effect of the sensors.

If you need to measure liquid levels, an ultrasonic level sensor is a good choice.

In the article “Level Senors for Tank Level Measurement“, we introduced a variety of level sensors that can be used to measure the tank level. Here, we will introduce the ultrasonic level sensor in detail.

Featured Sensors for Ultrasonic Level Measurement:

Features of Ultrasonic liquid level sensors

Ultrasonic liquid level sensors are non-contact level measurement devices. In the measurement, the ultrasonic pulse is sent by the sensor (transducer). The sound wave is reflected by the liquid surface and received by the same sensor or ultrasonic receiver. It is converted into an electrical signal by a piezoelectric crystal or a magnetostrictive device. It is transmitted and received by the sound wave. The time between the sensor and the surface of the liquid is measured. Due to non-contact measurement, the measured medium is almost unlimited. It can be widely used for measuring the height of various liquid and solid materials. Like: water level, fuel level, oil level, petrol tank level, and so on.

  • Accurate and reliable sensing method
  • Ultrasonic level sensor technology is ideal for difficult fluids where contact with the media is not desirable 
  • An ultrasonic liquid level transmitter is ideally sized and priced for most applications
  • Easy to install– simple to use
  • There are no moving parts
  • Temperature-compensated signal for improved accuracy
  • Self-cleaning sensor face
  • Unaffected by the target material’s color, shape or physical composition
  • Bench- or field-calibrated through communications with a PC or a push button on the sensor
  • Non-contact measurement, high performance, low cost, maintenance-free, high precision, long life;
  • Intelligent signal processing technology, the instrument adapts to various working conditions;
  • Two-wire system, three-wire system, isolated four-wire system
  • 24VDC, 220VAC power supply optional
  • Over-voltage, over-current, lightning protection
  • Photoelectric isolation 4-20mA current output

Advantages of Ultrasonic Level Transmitter

  1. No media contact for vertically mounted type, so flexibility for use on different corrosive media, thick fluids, slurries, wastewater
  2. Ultrasonic level transmitter has no moving parts. And it can measure level without making physical contact with the object.
  3. High temperature fluid compatibility for vertically mounted types, since no sensitive components make contact with the fluid
  4. High accuracy due to high frequency pulse wave and precise transit time time measurement
  5. The accuracy of the reading remains unaffected even after changes in the chemical composition or the dielectric constant of the materials in the process fluids.
  6. Operates with conductive or non-conductive fluids
  7. Sealed pressurised vessel will not affect performance
  8. Shorter blocking distance than radar
  9. Useful for measuring levels in tanks with corrosive, boiling and hazardous chemicals.

Disadvantages of Ultrasonic Level Transmitter

  1. Foaming, splashing, vapour and humidity can affect measurement performance
  2. High cost compared to other technologies
  3. Minimal blocking distance limits operation when in proximity to liquid level
  4. Temperature compensation required to compensate for speed of sound variation with air temperature
  5. Sound waves cannot be transmitted through a vacuum
  6. Shorter range than radar.
  7. It is not so convenient if the tank depth is high or the echo is absorbed or dispersed.
  8. The object should not be sound absorbing type.
  9. It is also unsuitable for tanks with too much smoke or high density moisture.

Extended reading: Guide to Ultrasonic Level Transmitters

What Is the Principle of Ultrasonic Level Measurement ?

Ultrasonic waves detect an object in the same way as Radar does it. Ultrasonic uses sound waves, and Radar uses radio waves. When the ultrasonic pulse signal is targeted towards an object, it is reflected by the object, and the echo returns to the sender.

The time traveled by the ultrasonic pulse is calculated, and the distance of the object is found.

Bats use a well-known method to measure the distance while traveling.

The ultrasonic level measurement principle is also used to find out fish positions in the ocean, locate submarines below water level, also the position of a scuba diver in the sea.

principle of ultrasonic level measurement

We will refer to Fig-1 and make an effort to understand the technicalities of the ultrasonic level transmitter.

An ultrasonic level transmitter is fixed at the top of a tank half filled with liquid.

The reference level for all measurements is the bottom of the tank.

The level to be detected is marked as “C”, and “B” is the distance of the ultrasonic sensor from the liquid level.

Ultrasonic pulse signals are transmitted from the transmitter, and it is reflected back to the sensor.

The travel time of the ultrasonic pulse from the sensor to the target and back is calculated.

Level “C” can be found by multiplying half of this time with the speed of sound in the air.

The measuring unit’s final result can be centimeters, feet, inches, etc.

Level = Speed of sound in air x Time delay / 2

Ultrasonic Level Measurement
Ultrasonic Level Measurement
TipYou can see our range of Ultrasonic Level Transmitters here.

Practical System Design Problems of Ultrasonic Level Transmitter:

The above principle of measurement looks quite straightforward and true only in theory.

In practice, there are some technical difficulties that are to be taken care of to get the correct level of reading.

  1. The velocity of sound changes due to the variation of air temperature.
    • An integrated temperature sensor is used to compensate for changes in the velocity of sound due to temperature variations.
  2. There are some interference echoes developed by the edges, welded joints, etc.
    • This is taken care of by the software of the transmitter and called interference echo suppression.
  3. Calibration of the transmitter is crucial.
    • Accuracy of measurement depends on the accuracy of the calibration.
    • The Empty distance “A” and measurement span “D” is to be ascertained correctly for inclusion in the calibration of the transmitter.
  4. The transient characteristics of the sensor will develop a Blocking distance as shown in Fig-1. Span “D” should never extend to the blocking distance.

The Basic Structure of an Ultrasonic Transducer:

structure of an Ultrasonic Transducer
structure of an Ultrasonic Transducer

An ultrasonic sensor is the heart of the ultrasonic level Transmitter instrument.

This sensor will translate electrical energy into ultrasound waves.

Piezoelectric crystals are used for this conversion process.

Piezoelectric crystals will oscillate at high frequencies when electric energy is applied to it.

The reverse is also true.

These piezoelectric crystals will generate electrical signals on receipt of ultrasound.

These sensors are capable of sending ultrasound to an object and receiving the echo developed by the object.

The echo is converted into electrical energy for onward processing by the control circuit.

Functional Block Diagram of a Typical Ultrasonic Level Transmitter:

We will refer to Fig-3 Functional Block Diagram to clarify the physical structures of an Ultrasonic Level Transmitter.

A micro-controller-based Control Circuit monitors all the activities of the ultrasonic level transmitter.

There are two Pulse Transmission Circuits, one for transmitter pulse and the other one for receiver pulse.

The pulse generated by the transmitter pulse is converted to Ultrasound pulses, by the Ultrasonic Sensor(Transmitter) and targeted towards the object.

This ultrasound pulse is reflected back as an echo pulse to the Ultrasonic Sensor (Receiver). The receiver converts this Ultrasonic pulse to an electrical signal pulse through the pulse generator.

The time elapsed, or the reflection time is measured by the counter. This elapsed time has relation to the level to be measured. This elapsed time is converted to level by the Control Circuit. There is a Timing Generator Circuit which is used to synchronize all functions, in the ultrasonic level measurement system.

The level is finally converted to a 4-20mA signal. 4mA is 0% level, and 20mA is the 100% level (see Fig-1).

This 4-20mA output signal carrying the level data can be transmitted to long distance to Process Control Instruments.

Functional Block Diagram for clarify physical structures of an Ultrasonic Level Transmitter.
Functional Block Diagram for clarify physical structures of an Ultrasonic Level Transmitter.

Common Applications for Ultrasonic Liquid Level Sensors

Ultrasonic liquid level sensors are used for liquid level, solid material level, the tank body, and open channel flow. Their performance is very good. Ultrasonic level sensors are also ideal for applications where continuous level measurement is required.

The most popular application of ultrasonic level sensors is to measure the level of liquid in tanks, wells, pits or lakes.If the container is linear, extrapolating the volume measurement is easy. In a non-linear container, a strapping table is usually used to adjust the reading to a certain volume as the level increases and decreases. Most of our ultrasounds are specifically designed for level measurement.Find the right sensor for you. Since ultrasonic sensors work without the need to touch the medium, they are ideal for difficult or corrosive liquids. Such as acids, wastewater, and others.

Typical Media:

  • Acids
  • Wastewater
  • Inks and Paints
  • Slurries
  • Food and Beverage
  • Semiconductor Process Chemicals
  • Oils and Petroleum Distillates

Another very popular application of ultrasonic sensors is solid level detection. The trick is actually to use a sensor with twice the required distance. This gives you a stronger signal, which in turn provides a better echo for the sensor’s measurements. You may also need to tilt the sensor mount so that it is perpendicular to the angle of repose.
Measuring solids has always been difficult. But ultrasound will still be the main condition for continuous non-contact measurement.

Open channels are the main means of transporting, filtering, and metering water. Open channel flow monitoring is used in water treatment plants, environmental monitoring, and irrigation canals. Ultrasonic sensors are an excellent choice for open channel flow.

open channel flow

Liquid Level Measurement with Ultrasonic Sensors

Tank level sensor

Tank level senor is a level sensor used to measure the tank level. The liquid level is the level of the liquid in a sealed container (such as a water tank) or an open container (water tank). The instrument that measures the liquid level is called a liquid level sensor, a liquid level gauge or a liquid level transmitter. The liquid level sensor is a kind of level instrument. Hydrostatic, Ultrasonic, Magnetostrictive, Radar, Differential Pressure are commonly choices for tank level measurement. Liquid level sensors have been around for decades for leak detection or level measurement. Common measured medium are: Water, Fuel, Diesel, Gasoline, diesel, liquefied gas, liquid ammonia, etc.

Ultrasonic level sensor wastewater

The ultrasonic level gauge is widely used in water level meter measurement projects in: Water plants. Wastewater treatment plants. Chemical reagent plants. Dye factories. Pulp mills and other factories. And is one of the main level measurement methods in modern intelligent automation industry. Ultrasonic technology has been used in the wastewater industry for more than 30 years for its high cost performance. Level gauges are widely used in industrial wastewater treatment plants and municipal wastewater treatment plants. Ultrasonic level gauges have the most applications, but their installation and measurement are limited by space.

In addition, since the propagation time of sound waves is affected by temperature, the ultrasonic sensor must be equipped with a temperature sensor. Ultrasonic level gauges are more accurate when used indoors or at groundwater levels.

ltrasonic level sensor wastewater

Outdoors, the ultrasonic sensor generates heat due to sunlight. This will lead to inaccurate compensation for the propagation time of the sound waves, which will cause measurement errors. In chemical plants, there are a lot of high-concentration gases over chemical liquids, which will also change the propagation time of sound waves and even absorb sound waves. The shortest distance that an ultrasonic sensor can measure is usually 10-50cm. When installing, consider the “blind zone” that cannot be measured.

Extended reading: Radar Liquid Level Sensor|Corrosive, steam, volatile liquids

Ultrasonic Level Sensor for Solids

Liquid level and material level measurement is a problem often encountered in the industry. Ultrasonic positioning technology has many advantages. It can not only locate and continuously locate but also conveniently provide the signals required by telemetry or remote control. Compared with radioactive positioning technology, ultrasonic technology does not require protection. Compared with laser-ranging technology, it has the advantages of simplicity and economy. At the same time, ultrasonic technology generally does not require moving parts, so it is relatively convenient to install and maintain. .The ultrasonic level meter can be widely used in: Petroleum, mining, power plants. Chemical plants, water treatment plants. Sewage treatment stations. Agricultural water. Environmental monitoring. Food (wine industry, beverage industry, additives, edible oil, dairy products). Flood resistance Flood control, hydrological monitoring. Open channels, spatial positioning, and many other industries. There are two main installation methods for ultrasonic level gauges, one is top installation and the other is bottom installation. The ultrasonic level gauge also uses liquid sound guidance. The ultrasonic probe is installed outside the bottom of the tank. The measuring liquid is transmitted to the liquid surface and then reflected back to the probe. The propagation time is directly proportional to the level of the liquid.

Common Questions for Level Measurement Applications:

Sino-Inst offers a variety of tank level measurement solutions. If you have any questions, please contact our sales engineers. CONTACT US

Sino-Inst’s Tank level sensors easily handle these liquids. Rugged construction. Corrosion resistant materials. A wide environmental operating range and a liquid-tight IP68 ingress rating make them ideal for indoor and outdoor use. Even in salt water and hydrogen sulfide (H2S) environments.
Products are offered in a variety of distance ranges to accommodate tanks. Ranging from 6 in (15 cm) to 50 feet (15.2m), with various mounting threads and accessories available.


Ultrasonic level gauges work well outdoors. But we also need to protect the ultrasonic level gauge.

Ultrasonic level gauge outdoor requirements:
     1. It is recommended to install a sun visor to extend the service life of the meter.
     2. Wire and cable protection pipes should be sealed to prevent water accumulation.
     3. Although the instrument has its own lightning protection device, it is recommended to install a special lightning protection device at the inlet and outlet of the instrument when the instrument is used in a lightning-resistant area.
     4. The instrument is used in particularly hot and cold places, that is, when the ambient temperature may exceed the working requirements of the instrument, it is recommended to add high and low temperature devices around the level gauge.

Yes, Sino-Inst offer explosion-proof ultrasonic level sensors for Hazardous locations.

Explosion-proof ultrasonic level gauge has built-in temperature compensation, self-adaptive power. And can have signal processing technology, which improves the measurement accuracy of the instrument. It has obvious suppression function for interference echo. The explosion-proof ultrasonic level gauge uses a metal-aluminum alloy die-casting housing. Which has a beautiful appearance and good protection ability. The instrument uses industrial isolated power supply. And all input and output lines have lightning protection, overvoltage, and overcurrent protection circuits.Explosion-proof ultrasonic level gauge is suitable for measuring corrosive mud or sewage, hydrochloric acid, sulfuric acid, hydroxide and other corrosive media. Ultrasonic level gauge can be applied to process tanks, daily tanks, pools, etc. The position meter is mainly used in oilfield, chemical, power, metallurgy and other industries.

Ultrasonic level sensor is a digital level instrument controlled by a microprocessor. In the measurement, the pulsed ultrasonic wave is sent by the sensor (transducer). And the sound wave is reflected by the surface of the object and received by the same sensor, which is converted into an electrical signal. The distance between the sensor and the measured object is calculated from the time between the transmission and reception of the sound wave. Due to non-contact measurement, the measured medium is almost unlimited. And it can be widely used for measuring the height of various liquid and solid materials.

Sure. Ultrasonic liquid level sensors can detect water level. Like wastewater, in tank, in river.

Sino-Instrument offers over 10 level transmitters for level measurement.

About 50% of these are liquid level meters,

40% is the tank level sensor.

A wide variety of level meters options are available to you,

such as free samples, paid samples.

Sino-Instrument is a globally recognized supplier and manufacturer of level measurement instrumentation, located in China.

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