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Measure urea concentration inline
without sampling, without waiting time

LiquiSonic® determines the urea content of an aqueous solution directly in the pipeline, tank, or bypass. The measured value is available immediately: during preparation, dosing, and receipt of delivered goods.
The ultrasonic method continues to operate reliably even when gas is carried in the solution and indicates when the gas content becomes excessive.

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Real-time measurement

Continuous monitoring without delay

Maintenance-free

No moving parts or wear components

Maximum accuracy

Precise measurement even under difficult conditions

Reduced operating costs

Cost-efficient solution with a short payback period

The concentration of a urea solution (internationally referred to as 'urea'), chemically carbamide or CH4N2O in water, can be determined via the speed of sound. It changes clearly and significantly with the urea content, and a LiquiSonic®sensor measures it directly in the medium - temperature-compensated, without sampling and without moving parts.

This covers the practically relevant cases: the 32.5% solution for SCR applications (AdBlue®, DEF, AUS 32 according to ISO 22241), the typically 40% reagent solutions for flue gas denitrification, and more highly concentrated solutions from urea production. Whether a solution meets specification is evident during filling rather than days later in the test report.

Why urea content is so often off in practice

Urea solutions all look the same: clear, colorless, and low-odor. You cannot tell from the liquid whether a batch contains 32.5% or 29%, whether there was condensation water in the tank, or whether a dissolving station mixed it too dilute. At the same time, the content tolerance is tight: for AUS 32, the permissible range is only a few tenths of a percent wide, and in denitrification it directly determines NOx emissions and ammonia slip.

Where the content shifts

  • Delivered goods do not match the ordered specification
  • Dissolving stations do not dose solids and water precisely
  • Residual quantities in the tank mix with a new batch
  • Flush water from lines dilutes the first cubic meters
  • Crystallized material changes the remaining solution

What follows from this

  • Claims and reversal of entire tank truck deliveries
  • Overdosing of the reagent and avoidable ammonia slip
  • Underdosing and therefore exceeded emission limits
  • Precipitation in nozzles, filters, and dosing pumps
  • Batches whose quality can no longer be verified afterward

Limits of common testing methods

  • Hand refractometer: fast, but only spot checks and highly dependent on reading
  • Density measurement: reacts sensitively to entrained gas and installation position
  • Labor titration: reliable, but too slow for release at the loading dock
  • Conductivity: urea does not dissociate, so the signal tends to reflect impurities
  • All spot samples show yesterday’s condition, not today’s

Our solution: LiquiSonic® in the urea circuit

The sensor sends an ultrasonic signal through the solution and measures its transit time over a precisely defined distance. This yields the speed of sound and, together with the simultaneously recorded temperature, the urea content.

Clear solution, cloudy solution, same result
Sound does not require a line of sight. Color, turbidity, and electrical conductivity play no role in the measurement result.

Temperature is measured along with it, not estimated
Urea solutions are sensitive to temperature. The sensor records it with high precision at the same location and compensates for its influence.

Gas in the solution: robust, but not without limits
The method handles entrained gas bubbles much better than density-based measurements. They change the shape of the received signal, which the sensor detects and reports to a certain extent. If the gas content increases further, it flags the measurement as uncertain instead of providing an incorrect value.

Sensor and evaluation unit separated
The signal is transmitted digitally. Up to 1,000 m can lie between the measuring point and the controller without loss of quality - practical for tank farms and transfer stations.

What operating personnel see at the system

The LiquiSonic® controller is located at the measuring point and shows the condition of the solution without detouring through the control room. For incoming goods inspection, a glance at the display is enough while the tank truck is being unloaded.

Tolerance band clearly highlighted
The bars on the left mark the permissible range. A value outside the specification is immediately noticeable without comparing numbers.

Trend over the entire batch
The trend view documents the receipt or preparation process seamlessly and can be archived.

Limit value switches as well
If the concentration leaves the band, this can be assigned to a digital output, for example to a shutoff valve at the transfer point.

Technical background

Concentration instead of proxy variable
Density, refractive index, and conductivity are auxiliary variables from which content is back-calculated, each with its own interfering influences. The speed of sound is also a physical property of the solution, but in the case of urea it depends particularly clearly on the content. Transmitter and receiver are positioned in a fixed geometry relative to each other, the measuring path is known, and the result is absolute and drift-free. Calibration data sets for common urea concentrations are stored; we can create additional ones.

Gas bubbles and their effect
During pumping, after dissolving solids, and at suction points, gas enters the solution. Ultrasound handles this much better than density-based methods because the signal still travels through the continuous liquid phase. Gas first becomes noticeable in the signal shape, and that is exactly how the sensor detects that bubbles are present. Beyond a certain gas content, there is also a limit here. Then the system reports it openly instead of silently outputting an incorrect value.

What pays off with this

Check product before it is in the tank
  • Nonconforming deliveries are detected upon receipt
  • No mixing of good and bad batches in the storage tank
  • Reliable figures for claims against the supplier
Use reagent precisely
  • Dose based on the actual content instead of the target value
  • Less ammonia slip due to unnecessary overdosing
  • Preparation processes hit the target on the first attempt
Reduce operating effort
  • Significantly fewer manual samples and lab analyses
  • No cleaning of optical surfaces, no wear parts
  • Factory calibration remains stable for years

Configuration for your measuring point

Installation

  • Immersion sensors with installation lengths from 92 mm to 3,000 mm
  • All common flanges, threads, and process connections
  • Pipe adapters for small and large cross-sections
  • Versions for potentially explosive areas available

Materials
Stainless steel is generally sufficient for urea solutions. Where additional components or cleaning media are required, Hastelloy and coatings made from PFA, ETFE or Halar are available.

Mixtures with accompanying components
If other components remain within known, narrow limits, the urea content will continue to be determined reliably. If two substances in the carrier medium are variable, such as urea next to a second salt, this can be resolved using additional measurements. We check this based on your recipe.

Quick overview
Measuring range, achievable accuracy, temperature and pressure level as well as material depend on each other and cannot be determined separately. We therefore design the sensor together with you and specify the values ​​that are reliable for your process.

  • Measuring principle: Ultrasonic transit time measurement, temperature compensated, inline
  • Measured variables: Urea concentration, speed of sound, temperature, indication of disturbances such as gas bubbles
  • Installation: pipeline, tank, bypass or transfer point; Length and connection depending on application
  • Interfaces: Analogue outputs, switching outputs for limit values, Modbus, Profibus, Profinet, Ethernet/IP
  • Maintenance: Maintenance-free, one-time factory calibration

Where urea is measured

Check product before it is in the tank

Blending plants, filling operations, and tank farms check the 32.5% solution during preparation and upon receipt. If a delivery deviates from the AUS 32 specification range, this becomes apparent at the transfer point instead of later at the customer’s site.

Flue gas denitrification, SCR, and SNCR

Power plants, waste incineration plants, cement plants, and glass plants often use reagent solutions around 40%. Inline measurement keeps the batch stable and provides the dosing control system with the concentration it is actually calculating with.

Production and further processing

In fertilizer and chemical plants, concentration is monitored during evaporation, intermediate storage, and blending—also when dissolving granules into liquid product and in urea solutions for resin production.

Specialized in concentration measurement for over 35 years

SensoTech develops and manufactures inline measurement technology for liquids in Magdeburg. LiquiSonic® Systems are used worldwide in the chemical industry, fertilizer production, power plant technology, semiconductor manufacturing, and the food industry.

35+

Years of experience

50+

Countries worldwide

ISO 9001

Quality certified

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Frequently asked questions

How can I tell that a delivered urea solution is incorrect?

Usually not at all, as long as only the delivery paperwork is checked. A solution that is too dilute cannot be visually distinguished from a correct one and often only becomes noticeable once it has long been mixed with the tank contents. An inline measurement at the transfer point provides the concentration during unloading and makes acceptance decisions possible.

Is urea solution the same as ammonia water?

No, even though both are used as reducing agents in denitrification and are often referred to synonymously in inquiries. Urea solution (urea, carbamide, CH4N2O in water) and ammonia water (ammonium hydroxide, NH4OH in water) are different chemicals with their own sound velocity curve. We configure the sensor for the medium actually used in each case. Just tell us which of the two you use!

Do you measure concentration or density?

Concentration. Density, refractive index, and conductivity are indirect methods: you measure a different property and calculate the concentration from it. We evaluate the sound velocity, which in urea solutions depends particularly strongly on concentration, and output the concentration directly. The sound velocity is available as an additional value.

Is the method suitable for AdBlue or AUS 32?

Yes. The narrow tolerance range around 32.5% is exactly the area where continuous measurement shows its benefits. Typical application points are preparation in the blending plant, inspection before filling, and incoming goods inspection at tank truck or IBC receiving stations.

What happens if there are gas bubbles in the solution?

A certain amount of gas does not interfere with ultrasonic measurement; the method is much less sensitive here than, for example, density measurement. Bubbles change the shape of the received signal, allowing the sensor to detect and report them to a certain extent. If the gas content becomes too high, the system marks the measurement as uncertain. It then does not output a seemingly plausible value, but a clear indication.

We currently work with a refractometer and lab sample. What changes?

Both remain useful as references, but they lose their role as the only source of information. Instead of individual points over the course of the day, you get a continuous profile that does not depend on who took and read the sample. There are no optical windows on the ultrasonic sensor that can become encrusted or fogged.

Does the measurement also work at 40% for denitrification?

Yes. The relationship between sound velocity and urea concentration can be used over a wide range, so both the 32.5% solution and the higher concentrations commonly used in SCR and SNCR systems can be measured. We tailor the appropriate calibration data set to your formulation.

What if the solution contains other components as well?

As long as accompanying components remain within known, narrow limits, the urea concentration can still be determined reliably. If two components in the carrier medium vary independently of each other, this can be resolved by additional measured variables so that both proportions can be output. We decide which variant fits based on your formulation.

Are there versions for hazardous areas?

Yes. Appropriate sensor and controller versions are available for plant sections with explosion protection requirements; we can meet the usual requirements. We determine which version is needed for your measuring point based on your plant’s zone classification.

Can I integrate the measured value into the control system and dosing control?

Yes. In addition to analog outputs, Modbus, Profibus, Profinet, and Ethernet/IP are available. Limit values can also be assigned to switching outputs, for example to close a valve if there is a deviation at the transfer point.

How complex are installation and maintenance?

The sensor is installed via an existing or newly added process connection and connected to the controller; nothing more is required. After that, there is no maintenance: no wear parts, no seals in the medium, no periodic recalibration.

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