單棒振動式物位開關之動態與穩定性分析

Abstract

振動式物位開關常應用於大型工業如石化工業、食品工業、化學工業中，監控液體、穀物、塑膠原料顆粒、礦物、各類粉狀至顆粒狀原物料於儲存槽中之狀況。最常見的振動式物位開關為音叉式，目前已有成熟的技術。然而音叉式開關在安裝時，因其結構為兩個叉體之探棒，故有機會使物料卡在於音叉探棒上的特性，需要注意安裝角度且定期清理以免影響其精準度造成誤判。因此本研究與合作公司桓達科技對外觀為一根單棒探棒的振動式物位開關為主要目標。目前對於單棒物位開關之研究非常稀少，故本研究主要利用有限元素法之商用模擬軟體Comsol Multiphysics進行單棒結構之自然共振頻與頻域分析。此研究主要目的為研究內振動管與外振動管之間的關係，並利用有限元素法模擬單棒之自然共振頻及其振幅，分析內外兩管振動之穩定性。接著重新設計結構，以安裝現有之音叉式物位開關所用之堆疊壓電元件與後端電路，設計出一穩定振動之單棒結構。透過調整各項結構參數，分析模擬結果影響自然共振的主要參數。依據模擬結果，製作出原型機測試其單棒結構之振動穩定性。最終測試其在以商用之壓電模組下，可探測到0.040g/cm3之低密度物料。文末總結單棒物位開關生產時，建議廠商加工時所須注意事項。

The vibrating level switches have been widely adopted in petrochemical industry, food industry, chemical industry for example to monitor raw materials such as grains, minerals, powder…etc. in tanks. Although the tuning fork type level switch is the most common vibrating level switch, it is prone to stuck some material between the probes when installed incorrectly or lack of cleaning. Hence, developing a vibrating rod-type level switch which has self-cleaning structure with robust accuracy is the main goal in this work. The method of designing the structure of the vibrating rod-type level switch is by Computer Aided Design (CAD), to define the parameters of the structure. Utilizing the finite element analysis software, Comsol Multiphysics, to analyze the eigenfrequency and force response of the level switch. This thesis mainly focuses on the relation between two probes and how it affects the vibration stability of the level switch. Based on the simulation result, prototypes were made to verify the vibration stability of the level switch. At the end, prototypes were tested by using the commercial piezoelectric module provided from Finetek and the results shows it can detect the low density granules down to 0.040 g/cm3 of density.