Browsing by Author "Van der Merwe, Jacobus Pieter"
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- ItemMagnetron output power controller used in the application of rooibos tea sterilisation(Stellenbosch : Stellenbosch University, 2019-04) Van der Merwe, Jacobus Pieter; De Swardt, J. B.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The objective of this project was to design a microwave sterilisation system that can be used to sterilise Rooibos tea. Rooibos tea is currently sterilised with a steam treatment, but this a ects the tea's colour and avour. Mi- crowave irradiation was investigated as an alternative form of sterilisation. Often microwave sterilisation tests are performed without the proper imple- mentation of microwave power control. Accurate microwave output power control was achieved by designing a custom magnetron power supply that uses a TRIAC to switch the mains voltage every half-cycle. A control system, that measures the applied and the re ected microwave power, was implemented to ensure a constant microwave power is delivered to the load. Calibrated mea- surements were taken of the system input power, microwave output power and applicator temperature. Adjustments were made to the microwave applicator to ensure that the dry tea did not burn. Microbiological tests were performed on the treated samples for Salmonella, E.Coli/Coliforms and aerobic plate counts (TVC's). The South African stan- dard for microbial safety of Rooibos tea was used as reference. The microwave sterilisation system worked well for Salmonella and TVC's, but E.Coli/Coliforms proved more resilient. A de nite batching problem was identi ed with the sterilisation of raw farm products that contain di erent concentrations of mi- croorganisms. This study provides a good foundation for any further research on the microwave sterilisation of Rooibos tea, as well as a range of hardware solutions for various other microwave power control applications.