Ultrasonic spectroscopy is the science of the behaviour of propagation of ultrasonic waves, due to changes in the environment. In most cases ultrasonic (high frequency sound) pulses are shot into the medium and returned echo’s are evaluated in a computer. This technology is widely spread in nature (bats and dolphins use this technology to detect movements or objects in their neighborhood), in fishing (to detect fish schools or determine the depth of the sea), in medical applications (while looking at unborn children in the mothers belly or for other medical applications) and in the industry in ultrasonic flow meters or for NDT applications.
Arenal PCS studies its behaviour for the determination of properties of fluids. The fact is that all fluids absorb, reflect and transmit ultrasonic pulses differently. As in most used pipelines or tanks the same type of liquid is present, the concentration of dissolved or suspended solids, the temperature and the density can be determined.

As Ultrasonic spectroscopy…

  • is a physical property and non-destructive technology
  • does not consume chemicals or reagents
  • is small sized and light weighted
  • can measure at 1000 Hz repeat frequency
  • can measure on a distance
  • can be made intrinsically or explosion proof
  • can be made sanitary
  • can be used under water
  • can be used on high or low temperatures
  • does not need consumables
  • does not drift and does not need frequent (or none at all) recalibration or maintenance
  • can be made in different embodiments and materials
  • does consume very little power

…this is one of the process analytical technologies for now and the future...

Which products are required for Ultrasonic spectroscopy?
A complete setup for ultrasonic spectroscopy consist always of the following parts:

  • Process Control Analyser (PCA)
  • 2x2 twisted pair cable from PCA to UDT
  • Ultrasonic Density Transmitter (UDT)
  • Coax cable from UDT to UDP
  • Ultrasonic Density Probe (UDP)
  • Teflon or POM sampling blocks

Connected to eachother, the following words explain how it operates:
The PCA is a ProFace HMI based PLC/Analyser that retrieves measurement data from the connected transmitters in the field. This data is validated and calculated into client specific parameters, like density, mass flow, efficiency, or anything. The PCA visualizes these results and takes care for connectivity to other PLC’s.
While powering the PCA, the PCA powers the UDT. In the UDT, voltage pulses are created and send throught the coax cable to the UDP. The UDP is the Ultrasonic Density Probe and consist of a piezo-sensitive material, which reacts tot his pulse quite intensively by generating ultrasonic waves. These waves are transmit into the probe. On changes of acoustic impedances from material to other material, a part of the echo is reflected back to the piezo element. These ultrasonic waves are, like magic, convert into voltage signal, like a sine. The probe is made in such way that many reflections are formed and converted. These are measured and stored in the UDT. These results are averaged and the deviation coefficient is determined for further analysis.
Mentioned above, measuring the acoustic impedance of materials is one of the key important properties that we analyze. But also the speed of sound in the material is of main importance. By combining these measurement, the physical property of the material (or fluid) “density” is accurately determined. Furthermore, by measuring the attenuation or dampening of the signal, the concentration of suspended solids is determines as well.
These properties can be explaned in more detail in the following echo’s:


One of the echo’s that returns to the piezo, is the one from the reflector. In water, the echo looks as above. The shape of the echo is depending on the transducer type and the pulser settings.
At a certain moment, the echo returns to the piezo. The vibration of the wave is converted to a voltage amplitude and read by the transmitter. A little later a second echo returns at the transmitter, which is a reflection caused by the first echo. It is lower, because some energy is absorbed by the probe and the piezo element and the water.
Suppose that we insert the probe in salt water. The following graph is formed:


The echo returns earlier to our unit. That means that the speed of sound is higher of salty water. As this is a physical property of the salt, by means of performing multiple calibrations, we are able to determine the concentration of the salt. Such calibration is valid for ever, as long as the medium is salt water. Suppose that the salty water contains sand, which is present in the probe, The height of the echo’s will drop significantly, which is recorded in the transmitter and the wt% suspended solids is determined. In case of air bubbles, the reflections get higher, which is otherwise not possible. An alarm is given as the echo may be lost from time to time. Combining the Ultrasonic spectroscopy technology with other analytical measurement technologies, like conductivity, pH, UVVIS Spectroscopy, Arenal can determine concentrations of dissolved solids in even more liquids.


Applications: In addition to the applications on this website, Arenal is focussed on:

1. Slurry density monitoring to replace radioactive Analysers. Apllications can be found in mining, dredging, drilling. Below you see four pictures of a 1-1/2"wafer for monitoring slurry density, TTS (Total Suspended Solids) and TDS (Total Dissolved Solids). In case of larger pipe diameters, only density monitoring is offered. The electronics are embedded in a small waterproof junction box and this is encapsulated in a polyethylene housing to offer solutions for submersible applications. Multiple sensors can be added to the wafer, f.e. pressure and flow.

7QB003-WFC-1-BT-S 7QB003-WFC-2-BT-S 7QB003-WFC-3-BT-S 7QB003-WFC-4-BT-S


2. Concentration monitoring of many industrial chemicals, like bases, salts, acids, oils;

3. Monitoring contaminations in pure liquids, like in d.i. water and alarming in case of changes;

4. Monitoring complete processes, like blending, cristallisation, settling, separation;

5. Spills monitoring in the sewage lines or in river water monitoring;

6. Monitoring COD (organic contamination) in sewage lines for WWTP in various types of industries.