Sensors - Dry Substance - Microwaves

Microwave (MW) technology has been applied to measure the water content of sugar products (liquors, juices, syrup) or massecuites and magmas. By difference, products dry substance (DS) can be calculated.
When a MW radiation pass through an aqueous medium energy is absorbed due to the polar character of the water molecule.
MW sensors measure the MW energy  absorbed by the solution in a certain radiation path. Normally the sensors are equipped with two antenna, one for MW emission and other or reception, separated by 4" (Theisen, Diringer, 2000).

These sensors, in sugar industry, are mainly used to evaluate DS in sugar solutions and to control sugar crystallization.

When  MW sensor is installed in pipes, the equipment must be placed after the pump, that is, in the compression side. The measurement is not influenced by liquid velocity (Theisen, Diringer, 2000).

For batch sugar crystallization, MW sensor is placed in the vacuum pan cone under the calandria. During boiling MW sensor determine the syrup DS during the concentration step before nucleation. After nucleation, in the presence of sugar crystal, it is not possible to measure the syrup DS if  the quantity of crystals are not known. To have this information it is necessary to measure the  DS of the syrup in the massecuite with another sensor, as a refractometer.
In trials in a refinery with samples of  all the boiling, 32 samples, the standard deviation of MW values compared with laboratory,was +/- o,24% in a DS range of 72-92% (Theisen, Diringer, 2000)

Bibliography
Theisen K-H, T. Diringer, 2000, Microwave concentration measurement for
              process control in the sugar industry, Proc. of  S.T.T. Conf., 79-92

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