A contribution to the development of moisture measuring of vacuum-dried hygroscopic materials

Sušenjem higroskopnih materijala, a naročito voća (borovnica, kupina, malina, itd.) i nekih vrsta povrća u vakuumskim sušarama zračenjem pri niskoj temperaturi, zadržavaju se njihova izvorna kakvoća i ljekovita vrijednost. Provedena su pokusna istraživanja primjenom metode kapacitivnog mjerenja snižavanja vlage plodova borovnice sušenih u vakuumu u cilju provjere metode i doprinosa mogućem razvoju primjenjivih uređaja. Korištena je realna vakuum komora sa zračećim pločastim električnim grijačima i pripadajućom funkcionalnom i regulacijskom opremom. Projektirani i izrađeni su mjerni senzori te je sklopljen i programiran mjerni uređaj. Promjenom vrlo malih vrijednosti električnog kapaciteta potvrđena je mogućnost mjerenja snižavanja vlage plodova borovnice pri provedbi režima sušenja. Istaknuta je uska povezanost preciznosti regulacije radnih parametara (podtlak, temperatura) u komori s točnosti mjerenja vlažnosti materijala. Interdigitalnim senzorom postignuta je prihvatljiva osjetljivost mjerenja vlažnosti sušenog materijala. Predložene su smjernice daljnjeg istraživanja i mogućeg razvoja primjenjivog mjernog uređaja.Dehydration of hygroscopic materials, especially fruit (blueberries, blackberries, raspberries, etc.) and some types of vegetables in vacuum dehydrators by means of radiation at low temperatures preserves their original quality and medicinal value. Experimental research has been carried out, whereby the moisture reduction of vacuum-dried blueberry fruits was measured by applying the capacitive measuring method, in order to check the method and contribute to possible development of applicative devices. A real vacuum chamber with radiating plate electric heaters and additional functional and regulation equipment was used. Measuring sensors were projected and made, and a measuring device was assembled and programmed. By changing very low values of capacitance, the possibility of measuring moisture reduction in blueberry fruits during drying was confirmed. A close connection between the regulation precision of working parameters (subpressure, temperature) in the chamber and the accuracy of measuring the material moisture was underlined. By using an interdigital sensor acceptable sensitivity in measuring the moisture of dried material was achieved. Guidelines for further research and possible development of an applicable measuring device were suggested