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For liquids that are composed of two dissolved components, such as acid/salt mixtures, alkaline/salt and other mixtures existing of three major components, Rhosonics has developed an advanced inline analysis system.
The Model 9570 employs three fundamental components. One of which is an inline ultrasonic sensor, the second is an inline electrodeless conductivity analyzer and the third is formed by the controller, Model 9570. Principle of operation The system employs the measurement of two physical parameters. The first parameter is the sound velocity.
Pure water, without any ingredients, has a specific speed of sound. At room temperature, the sound velocity of water is near 1500 m/s.
When salts are added to water, normally the sound velocity will change drastically, in most cases between 5 to 10 m/s per weight %. The relationship between concentration and sound velocity is well defined, and usually follows a remarkeable straight line, making it an ideal parameter for acurately measuring salts, in particular at high concentrations.
Alkalines also have an even more drastic effect on the sound velocity. This is particularly true for KOH and NaOH, where the sound velocity increases with an incredible 25 m/s per weight %. This phenomenom is making the standard version of the Model 9570 to a reliable tool for inline measuring of alkalines. The temperature has some effect too, however the Rhosonics 9750 measures the temperature accurately and automatically compensates for this effect.
A particularly nice feature of acids is that they too affect the sound velocity, but in many cases in a reverse manner. In other words, the sound velocity will decrease when the concentration increases. This is particularly true when the temperature is above room temperature.
In a mixture of an acid and a salt, the sound velocity will therefore be increased by the salt, and decreased by the acid. What this means for the ternary analysis principle, will be explained later.
For measuring the conductivity, the Model 9570 employs an electrodeless inductive conductivity meter. The probe is made of acid resistant polypropylene or PEEK.
The conductivity of water is, in contrast with the sound velocity, zero. Therefore, in many cases, the conductivity will be affected in a positive manner by both acids and salts.
In addition, it is a well-known fact that acids give a larger increase in conductivity than salts. Rhosonics has developed an algorithm for defining conductivity and the sound velocity, based on the concentration of the two components and the temperature. By reverse modelling, the Rhosonics calculates the concentration of both components from the measured variables. Performance characteristics | | Range | Resolution | Accuracy | | Temperature circuit | -10...200 degC | 0.001 °C | 0.005 degC | | Sound speed circuit | 500-3000 m/s | 0.002 m/s | 0.01 m/s | | Recorder outputs (2x) | | 0.025 % of FS | 0.1 % of FS |
| Total Accuracy of measurement | HF or HCl (0-1 wt%): better than 0.005 wt% | | | HF or HCl (0-10 wt%): better than 0.01 wt% |
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