Ultrasonic Level Transmitter Principle, Limitations, Calibration and configuration

As the name suggests, a level measurement transmitter is an instrument that provides continuous level measurement. It can be used to determine the level of liquid or bulk solid at a given time. Levels of media such as water, viscous and combustible fluids, or dry media such as bulk solids and powders can be measured using the transmitter.

Level measurement transmitters are used in a wide variety of applications that require level measurement within containers or tanks. These transmitters often find their application in the materials handling, food and beverage, energy, chemical, and water treatment industries.

An ultrasonic level transmitter is attached to the tank’s top and sends an ultrasonic pulse down into the tank. Ultrasonic waves work in the same way as radar does in detecting an item. Radar employs radio waves, while ultrasonic uses sound waves.

When an ultrasonic pulse signal is directed at an object, the item reflects the signal, and an echo is returned to the sender. The distance of the item is determined by calculating the time taken by the ultrasonic pulse. Bats employ a well-known method of distance measurement.

Ultrasonic sound is sound that is above the human hearing range. The human ear can only hear up to a frequency of 20 kHz. Ultrasonic frequencies are those that are greater than 20 kHz. In industries, ultrasonic waves are used to monitor the level of liquids and solid items.

Ultrasonic level measurement is a contactless method for measuring the level of hot, corrosive, or boiling liquids. The ultrasonic level transmitter instrument’s heart is the ultrasonic sensor.

Electrical energy will be converted into ultrasonic waves using this sensor. For this conversion, piezoelectric crystals are used. When electric energy is given to piezoelectric crystals, they will oscillate at high frequencies. It’s also true in the other direction.

On receiving electrical inputs, these piezoelectric crystals will create electrical signals. These sensors have the ability to emit ultrasound to an object and then receive the item’s echo. The control circuit converts the echo into electrical energy for further processing.

Measurement principle

The time of flight principle is used in continuous noncontact ultrasonic level measuring. The time between the sensor transmitting sound energy to the surface of the measured material and the echo returning to the sensor is measured by an ultrasonic level instrument.

The distance to the surface is computed using the speed of sound as measured via the travel medium at a certain temperature. This distance measurement can be used to calculate the level.

Even in narrow, obstructed, or agitated vessels, the instrument’s built-in echo processing can allow it to determine the material level of liquids, solids, or slurries.

Limitations

Ultrasonic level measurement is rarely employed in upstream hydrocarbon process streams; nevertheless, it may be used in atmospheric utility applications. Compensation reference pins should be utilized in applications that are subject to vapor density variations.

The maximum measurement distance should be validated against the technology (reflectivity may be lowered above 30 m, resulting in a measurement error). Ultrasonic sensors have a blocking distance (near to the sensor) beyond which they cannot reliably measure, for example, 0.25 metres.

The vessel pressure should be limited to about 0.5 bar or less. The level measurement may become more unreliable as the pressure rises. Vapour, vacuum and temperature gradients can all affect the speed of sound, resulting in inaccurate observations.

Unreliable measurements can be caused by the presence of foam or severe turbulence on the surface of the material being monitored.

Selection

Because the ultrasonic measurement is noncontact, it can be used to measure even abrasive or hostile materials. When choosing an instrument with an appropriate minimum and maximum range, consider the vessel height and headroom.

Design

Ultrasonic sensors should be built of a material that is compatible with the medium being monitored (e.g. PVDF or ETFE) A reliable, low-maintenance product is provided by solid construction and a self-cleaning action on the sensor’s front.

The use of a submergence shield on a sensor will allow an ultrasonic instrument to operate in potential flooding situations, either notifying a full vessel to a control system or continuing to operate pumps to clear the flood.

Calibration and configuration

  • BD : Blocking Distance
  • SD : Safety Distance
  • E : Empty Calibration ( Zero Point )
  • F : Full Calibration ( Span )
  • D : Nozzle Diameter
  • L : Level

Performing an initial or “empty calibration”: “input” the distance E from the sensor face to the minimum level in this concept (zero point). It’s worth noting that the zero point in containers with parabolic roofs or bottoms should not be further away than the point where the ultrasonic wave reflects from the tank bottom.

For maximum empty tank performance, a flat target plate parallel to the sensor face and directly below the sensor mounting point should be attached to the bottom of the vessel. The high calibration point, or 100 percent full point, can be set after the empty distance has been set.

Setting the distance from the sensor face to the 100 percent full level or inputting a span (level) from the 0 percent or low calibration point to the 100 percent full level are two ways to accomplish this.

Ensure that the 100 percent full or high calibration point does not enter the corresponding sensor’s “blocking distance” or “blind zone” during commissioning.

This will differ depending on the sensor. Blocking distances or blind zones can be increased to eliminate false high-level reflections created by obstructions, however, due to the sensor’s physical restrictions, they can only be reduced to a specific distance.

It is recommended that the maximum level (distance F/full span) be set. Both the BD ‘blocking distance’ and the SD ‘safety distances’ should be factored into this distance F. Where BD denotes a dead zone where the wave is unable to make any measurements, and SD denotes a warning or alarm zone.

Types of Level Measurement Transmitters & How Do They Work?

As the name suggests, a level measurement transmitter is a device that provides continuous level measurement. It can be used to determine the level of liquid or bulk-solid at a particular time. Levels of media such as water, viscous liquids, and fuels, or dry media such as bulk solids and powders can be measured using transmitters.

Level measurement transmitters are used in a myriad of applications that require level measurement within containers or tanks. These transmitters often find their application in the material handling, food and beverage, power, chemical, and water treatment industries.

Working Principle of Level Transmitters

The principle of operation of the above-level transmitters varies according to their underlying principle. For example, capacitance level transmitters operate by means of a capacitor, hydrostatic level transmitters rely on the pressure of the fluid in a storage container to measure the level, while ultrasonic level transmitters rely on the ultrasonic wave to determine the level. Converts the distance traveled.

However, all of these level transmitters measure levels in three ways: fluid weight fluid pressure head. The state of a liquid in a container. If you look closely, all of the pressure transmitters included in this publication take into account one of three factors to obtain a proper measurement. Level measurement is classified into two types: direct and indirect level measurement or done by contact or non-contact transmitters.

Posted in PLC

Leave a Reply

Your email address will not be published.