Level Measurement

Ultrasonic Level Transmitter Working Principle

Ultrasonic Sensors Measurement Principle

         Ultrasonic transducers transmit and receive sound waves using piezoelectric components. When a voltage is provided, the piezo components start to vibrate. High-frequency soundwaves are created by this vibration. These impulses are reflected by the target, and an echo is sent back to the ultrasonic transducer. The distance can be determined using the speed of sound in the air by observing the amount of time it takes for the echo to return.

Ultrasonic Level Sensors Frequency

         Depending on frequency of Ultrasonic waves small or large ultrasonic transducers. Frequencies of 20 kHz or above are the defining characteristics of ultrasonic soundwaves. The typical ultrasonic sensor frequency range is 20 kHz to 1MHz.

         For air-coupled applications, ultrasonic transducers operate at frequencies between 30 and 500 kHz. The rate of attenuation increases as the ultrasonic frequency rises. Consequently, low-frequency sensors (30-80 kHz) are more useful for long range, whereas high-frequency sensors are more effective for short range.

The ringing-decay is further lessened with higher frequency sensors (80–500 kHz), enabling a smaller minimum detection range. Transducers in the 1-MHz band are frequently utilized for liquid level sensing

  • High frequencies (>150kHz) uses small transducers in the short range of higher absorption by the air.
  • Low frequencies (<150kHz) uses larger transducer in the long range of higher sound pressure.

What is meant by ultrasonic level measurement & where it can be used?   

Ultrasonic level measurement is contactless principle and most suitable for level measurement of hot, corrosive and boiling liquids. It does not require contact with processed material. It provides continuous level measurement.

  • The ultrasonic level measurement is suitable for measurement in liquid and solid.
  • Ultrasonic level transmitter is used to measure the level in depth.
  • Ultrasonic level transmitter is used to measure the level of acids and bases.
  • Ultrasonic level transmitters are non-contact, low-cost, and easy to install.
  • They are used to measure hot, corrosive, and boiling liquids and other solid objects.
  • Ultrasonic level measuring typically uses 40–200KHz frequencies.

What is the basic concept of Ultrasonic level measurement?

         The basic concept of ultrasonic level measurement is that a sound wave is emitted from the transducer and travels through the air or gas medium until it reaches the surface of the liquid or solid material. When the sound wave encounters the surface, it is reflected back to the transducer, which then measures the time it takes for the sound wave to travel to the surface and back. This time is directly proportional to the distance between the transducer and the material surface, and thus the level of the material can be determined

What is the working principle of ultrasonic level transmitter?

  • Ultrasonic level sensors transmit pulses towards the surface and then receive echoed pulses back. This method is known as the time of flight principle.
  • Fundamentally the transmitter splits the time between the pulse and its echo by two, and that is used to compute the distance to the surface of the liquid or substance.

What are the element in ultrasonic level measurement?


A transducer is a major component of measurement. This device transmits and receives sound waves. A high-frequency sound pulse is sent towards the surface of the substance being measured by this device, which is typically positioned on top of the tank or vessel.

Signal processor

The signal processor receives the transducer’s signal and processes it to calculate the material’s level. It measures the time it takes for the sound wave to travel to the surface and back and determines the distance to the material surface.


The unit’s display reveals the material’s level in the tank or vessel. Simple analogue displays are also possible, as well as more sophisticated digital displays with extra functionality like alarms and control outputs are also available.

Power supply

The transducer and the signal processor are given the necessary electrical power by the power supply.

Working of Ultrasonic Level Measurement

  • The basic idea behind how ultrasonic level instruments work is that they use sound waves to measure the level of liquids, solids, and slurries.
  • They can monitor open channel flow, ascertain the real volumetric throughput at lift stations, detect differential level, and manage the pumps in addition to performing standard level or volume measurements.
  • A high efficiency transducer and an associated electrical transceiver make up ultrasonic level transmitters.
  • They work together to calculate how long it takes an ultrasonic pulse to travel from the non-contacting transducer to the level of the sensed substance and back again.
  • A transducer situated on the top of the tank sends waves onto the surface of the material whose level is to be detected in bursts, as shown in Figure.
  • Within the transducer, a piezoelectric crystal transforms electrical pulses into sound energy, which propagates as a wave at the defined frequency and at a consistent speed across a particular material.
  • Echoes of these waves return to the transducer, which performs computations to convert the distance of wave travel into a measure of level in the tank.
  • The distance between the transducer and the material in the vessel directly proportionally affects how long it takes to hear the return echo after the sound burst is fired.
  • The surface of the substance is typically covered in air as the medium, but it might also be a layer of other gases or vapours.
  • The bursts’ descent to the reflecting surface and return are timed by the sensor.
  • Thisi time can be used to calculate the level of fluid in the tank because it is proportional to the distance from the transducer to the surface


Ultrasonic level transmitter
  • The following equation provides an example of the fundamental idea at the basis of ultrasonic measurement technology:

Distance  = (sound speed times time)/2.

  • There are sensors on contact devices that can output readings as 4-20 mA signals to DCSs, PLCs, or other remote controls.
  • The range of ultrasonic frequencies is between 15 and 200 kHz. Higher frequency instruments are utilized for shorter liquid level measurements, while lower frequency ones are employed for more challenging applications including measurements over longer distances and of solid levels.

Minimum measuring distance(Xm)

  • All ultrasonic level meters share the same minimum measuring distance (Xm), commonly referred to as the “Dead Band”.
  • There is a small area in front of the sensor that the ultrasonic instrument cannot measure.

Maximum measuring distance (XM)

  • The largest measurement range that the gadget is capable of in ideal circumstances.
  • Beyond this distance, there is no way to quantify anything.

Advantages of Ultrasonic level transmitter

  • Easy to install
  • No moving parts
  • No contact with medium
  • Less maintenance

Disadvantages of Ultrasonic level transmitter

  • Ultrasonic level transmitters measure between 0.3 and 30 metres. Applications with a measurement range greater than this limit are unsuitable.
  • Obstacles can reflect or absorb ultrasonic signals. This may lead to inaccurate readings.
  • Ultrasonic level transmitters’ accuracy can be affected by material type, foam or turbulence, container form, and size.
  • Ultrasonic level transmitters cost more than radar or capacitive sensors. Maintenance: Ultrasonic level transmitters must be cleaned, calibrated, and replaced regularly.

Limitation of ultrasonic level transmitter

  • Depends on the quality of echo
  • Inconvenient if the tank depth is high or the echo is absorbed or dispersed
  • Is unsuitable for tanks with too much smoke or high-density moisture
  • Temperature compensation is essential.

What are the factors to be considered in practical applications of ultrasonic measurement method?

  • Air temperature affects sound speed. The transducer may have a temperature sensor to adjust for changes in operational temperature that would influence the speed of sound and consequently the distance calculation that yields an accurate level measurement.
  • Heavy foam/dust can absorb sound. Absorption may prevent ultrasonic use.
  • Severe liquid turbulence can change readings. This issue may be solved by instrument dampening or response delay. The transceiver dampens the maximum material level change and mA output signal volatility.
  • Damping reduces display responsiveness when liquid surfaces are agitated or material falls into the sound path during filling.

Industrial Ultrasonic Level Sensor Applications

Due to the no-contact method of measuring, several industries utilize ultrasonic sensor technology. Applications for industrial ultrasonic sensors include:

  • Processing of food and beverages
  • Medical devices
  • Trash management, commercial carwashes, pump solutions, and so much more!
  • There are sanitary solutions available for a few applications, such as medical ultrasonic sensors.

Explain working of Ultrasonic transmitter placed in a tank.

  • Consider measuring a tank’s liquid level continuously.
  • We install a tank-top ultrasonic level transmitter for this.
  • At 5 times per second, this sound wave is emitted onto the target.
  • The transducer receives echo sound signals and converts them to electrical signals.
  • An electrical signal processor checks the target’s echo against walls, beams, pipes, and other barriers.
  • It calculates ultrasonic wave travel time from transducer to echo.
Ultrasonic transmitter with tank
  • Processor now calculate the distance to the target surface from the device using the formulae

                  Distance = (Speed of sound in air x Time of Flight ) / 2

  • Once the transmitter is programmed with the height of the tank, the level of the target in the tank is calculate by the microprocessor using the formula,

         Level of target = Total tank height – Distance of target from the device.

List few ambient factors which have impact on ultrasonic level measurement system.

  • Humidity Variations
  • Variations in temperature and atmospheric pressure

Define main parts of Ultrasonic sensors.

  • The ultrasonic transducer, a component of the sensor and receiver;
  • The ultrasonic transmitter, which generates the pulse;
  • The ultrasonic receiver, which records the returning sound.

What is meant by Ultrasonic Transmitters & Crosstalk

  • Crosstalk happens when the signals from two ultrasonic level sensors interfere with one another, giving false readings.
  • To ensure a high level of functional safety, you can simply eliminate this issue by synchronizing or multiplexing your ultrasonic sensor system.

Synchronization of ultrasonic sensors.

All of the received echoes are sent and evaluated simultaneously by ultrasonic transmitters. This feature can be used right away once all the ultrasonic sensors are connected.

Combining ultrasound sensors.

  • This mode causes ultrasonic transducers to solely evaluate their own echoes because the ultrasonic sensor provides the signal sequentially.
  • Maximum connection is up to four sensors.
  • Following the application of the working voltage, ground (GND) connection to retain for a minimum of five seconds. There is a little operational delay brought on by multiplexing.

What is meant by blind zones in ultrasonic transducer.

  • Sensors contain ultrasonic transducers that alternately generate sound waves and detect the echoes that are reflected.
  • After producing a pulse, the transducer keeps vibrating, making it unable to instantly pick up echoes.
  • Due to the delay, there is a blind zone where no precise or trustworthy measurements can be made.

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