3 General principles
PIOX R721
3.1 Measurement principle
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UMPIOX_F72xV1-3EN, 2021-09-01
Determination of the concentration
The concentration is determined with the refractive index.
The refractive index depends on the temperature and concentration of the fluid. This relationship between temperature,
refractive index and concentration is depicted with a function. The coefficients and the function are stored in a fluid data
set.
Temperature compensation
For industrial applications, it is often necessary not to determine the refractive index of the measured fluid temperature but
rather at a reference temperature. The transmitter converts the refractive index.
In case temperature coefficients for the fluid are stored, they will be used to calculate the refractive index at a reference
temperature.
Multi-component system
Apart from the refractive index and the temperature to determine the physical quantity for analysis, other physical
quantities (e.g., sound speed, density, conductivity) are needed if the fluid consists of more than 2 components. These
physical quantities are read via the inputs and processed with the fluid data set stored in the transmitter.
Fig. 3.2: Characteristic curves (example for saccharose solution)
1.5000
1.4500
1.4000
1.3500
10
20
30
40
50
60
70
80
refractive index
concentration
temperature [°C]
20
50
80
