Ultrasonic concentration analyzers
Here at Rhosonics, we continuously work on improving our analyzers and sensors. Since the introduction of the first analyser in 1992, Model 8000, the available amount of applications, models, and variants has been increased dramatically. We can help you by adapting our solutions to improve your production processes.
Both the models 8000 (1992) and 8100 (1995) are still used worldwide. These analyzers are sometimes upgraded in our facility to enable them to work in new production processes used by the same client. Sometimes, we recommend clients to use a new analyser, which has more features and, because of newer sensors, is generally at least ten times more accurate.
Thanks to a highly innovative design with respect to electronics and sensor technology, continuous and extremely accurate in-line monitoring of fluid mixtures is now, with virtually no need for regular maintenance due to the lack of moving or degrading parts.
The core of the system is the cell, in which ultrasonic waves are generated and received. This cell can be mounted externally, in a bypass, but can also be deployed as a measuring section, where the liquid is analyzed while it flows through the pipe. Several probe designs aid the measurement of density inside tanks and pipelines.
The ultrasonic transducer generates short, highly dampened ultrasonic pulses in the frequency range between 1 and 7,5 MHz. These sound waves propagate through the liquid with a yet unknown speed until they reach a second transducer, which converts the received sound waves into electrical pulses.
We work with different ultrasonic technologies, per application we determine which technology is used.
- Our first technology calculates the speed at which the sound travelled through the liquid. This is done by registrating precisely when the signal was received. The speed at which sound travels through a liquid is affected by the fluid’s density and the modulus of the substance’s compressibility. The speed of sound is mostly used for concentration measurement in binary or ternary (chemical) liquids. Based on temperature, path length, and application, the concentration or density of a liquid can be determined very accurately by means of a polynomial equation.The constants of the polynomial equation are entered though a touchscreen or via (touch)-buttons. These constants are known for many liquids and have been determined in the Rhosonics laboratory.
- Our second technology determines the rate of loss of energy of the pulses (attenuation). Energy loss is the result of action by particles. We can determine the amount of solids in slurries, sludge, or in the production of polymers.
- Our third technology is based on the acoustic impedance through the Sir Rayleigh Physics law and is used to determine the slurry density in-line and real-time. You can find more information about this technology at our section: "Slurry density measurement applications".
Slurry density measurement applications
Mineral processing plants, dredgers and construction sites want to know the density of their slurry to determine the concentration of solids which is flowing through the pipe. In this case we would use our Slurry Density Meter (SDM). For slurry density measurement applications we use the ultrasonic acoustic impedence technology. The density measurement is based on the acoustic impedance method through the Sir Rayleigh Physics law. Please see the formula below.
ZL = ρL * CL
Acoustic impedance (ZL) = Density (ρL) * Speed of sound (CL)
The Acoustic Impedance (ZL) is measured and the Speed of Sound of water (CL) is known, therefore the Density (ρL) can be calculated.
Measuring Acoustic Impedance
A piezo element (a small crystal piece) inside the sensor tip is used to create (and measure) an acoustic signal. Differences in acoustic impedance of materials causes this acoustic signal to be (partially) reflected. By measuring the strength of the reflected acoustic signal the acoustic impedance of the material can be determined. As the density of liquid increases so does its acoustic impedance causing a decrease in strength of the reflected signal (see figure below).
Naturally, not all liquids can be measured using ultrasonic measuring technology. In many cases, the 8500 is the ideal choice for your in-line process analysis.
Acids form one category of liquids that can be measured with a high degree of accuracy. Most acids possess such an extremely high change in sound speed compared to density, that the accuracy of the measurement is comparable to that performed in laboratory analysis. Examples of such acids include sulphuric acid, nitric acid, hydrochloric acid, and phosphoric acid.
Bases have sometimes an even more astonishing change in the speed with which sound travels through the liquid in question. Looking at the graph of potassium hydroxide, you will find that a sound velocity change of about 25 m/s is more than enough to ensure a highly accurate analysis.
Alcohols, such as glycol, ethanol, and methanol, are also easy to measure accurately.