基於電壓調整機制之超音波濃度量測動態範圍自動校正系統

Automatic Dynamic Range Correction of Ultrasonic Concentration Measurement System Based on Voltage Regulator Mechanism

許伯瑜(Po-Yu Hsu)

指導教授 ： 宋家驥

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202104498

摘要

台灣位處太平洋，四面環海，每年都遭受數個颱風侵襲，這樣的情形造成水庫淤積率逐年攀升。擁有非侵入、即時性等特點的超音波檢測技術是監測泥沙濃度的主要方法之一，以壓電片製成的超音波換能器更是這個系統裡的核心元件。本論文即是為了提高可量測的泥沙濃度動態範圍所設計之一發一收電路系統。
系統接收電路以AD8310對數放大器為主體，將接收換能器接收到之1MHz弦波訊號轉換包絡線再經由ADC輸出數位訊號給ARM微處理器分析。然而，由於AD8310有其動態範圍的限制，過強的發射電壓會造成低濃度變化無法準確地被偵測，為了提高整體量測的動態範圍，本研究設計出了一套能夠自動在三種發射電壓中選擇最適宜待測濃度之發射電壓的系統。
透過ARM微處理器控制功率放大器、電壓調整電路，以達成利用不同大小的發射訊號供給超音波換能器。其中功率放大器採用切換式功率放大器，利用電晶體使開關達到ZVS提高輸出效率。電壓選擇電路則是利用三個LDO直流穩壓器分別連接電晶體，利用GPIO接口控制開關，供給發射電壓給功率放大器，達成自動掃瞄不同發射電壓。
驗證方面，利用高嶺土製作不同濃度的懸浮液體，而電壓調整電路選用了三種穩壓器，分別為0.8V, 1.5V, 2.5V，以各個電壓分別進行測量，搭配理論校正後之率定曲線，對量測後的實驗數據進行比對。對照後發現，單一發射電壓之動態範圍會受到雜訊或者過高濃度干擾，量測時會有所受限。改以多發射電壓進行量測，搭配動態偵測，自動切換適合量測環境之發射電壓，量測時大約可提高5dB左右之動態範圍，且在低濃度量測時也比單一發射電壓表現來的好，此結果將有助於提供超音波濃度量測系統一個可行的發展方向。

關鍵字

超音波 ； 切換式功率放大器 ； LDO ； ARM ； 泥沙濃度 ； 電壓調整

並列摘要

Located near the Pacific Ocean, Taiwan could be hit by several typhoons every year. It leads to a rising rate of reservoir siltation. Ultrasonic detection technology with features such as non-invasiveness and real-time is one of the main methods for monitoring sediment concentration, and ultrasonic transducers made of piezoelectric sheets are the core component of this system. This thesis aims to explore the underwater transceiver circuit system designed to increase the dynamic range of the measurable sediment concentration.
The receiving circuit takes AD8310 as the main body, converts the 1MHz sine wave signal into an envelope, and then outputs through the ADC to the ARM to analyze. However, due to the dynamic range limitation of AD8310, if the emission voltage is too strong, the lower concentration change will not be accurately detected. In order to improve the dynamic range, this research has designed a system that can automatically select the most suitable emission voltage for the concentration to be measured among the three different emission voltages.
The power amplifier and voltage regulator circuit are controlled by the ARM to supply ultrasonic transducer with different signal. Switching power amplifier is adopted, using transistor to make the switch reach ZVS to improve the output efficiency. Three LDOs are used to connect the transistors respectively, and the GPIO is to control the switch in order to supply the transmitting voltage to the power amplifier, so as to achieve automatically scan for different transmitting voltages.
Kaolin is used to make suspensions of different concentrations. Three voltage regulators, 0.8V, 1.5V, and 2.5V are used to measure respectfully with a view to compare the experimental data with the calibration curve after theoretical correction. It is found that the measurement of the dynamic range of a single emission voltage will be limited by noise or excessive concentration. Measuring with multiple emission voltages with dynamic detection allows us to automatically switch to the emission voltage suitable for the environment, which can increase the dynamic range by about 5dB with a better performance than a single emission voltage when measuring at low concentrations. Hopefully, the result of this thesis will help provide a feasible development direction for the ultrasonic concentration measurement system.

並列關鍵字

Ultrasonic ； Switchable Power Amplifier ； LDO ； ARM ； Sediment Concentration ； Voltage Regulator

參考文獻

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