Design Of A Portable Measurement System For QCM Liquid Detection

Based on the QCM measurement status, the paper tells the disadvantage of two methods measuring QCM. The first method is using a oscillatory circuit, which will stop working while applied in liquidoid. The second method is to use a Network Analyzer, but, huge and expensive, it can’t be used in a lot of condition such as in the open air. So a small, chip, accurate measurement system is necessary. The paper is initiated based on the situation.The signal sent to QCM sensor is generated by a signal generator device and after goes through the QCM sensor, it goes to a scope meter. Then we can read the resonant frequency on the scope meter. The value of signal can reach the maximum while the frequency is resonant frequency. The signal generator device must meet three conditions: firstly, the accuracy must reach 1Hz. Secondly, the amplitude decay must keep unchanged. Thirdly, the value must have a dynamic adjustment function, and work in different modes, including dot frequency and sweep frequency. Such requirements will told in the paper next.According to the above requirements, I do the following works:1. Design a signal generator based on the AD9854 chip. Using the AD9854 as the main working chip, which can generate signal frequency and sweep frequency. While working in the signal frequency, the value can be set to any value in the pass-band, and while working in the sweep frequency mode, the maximum frequency and minimum frequency and frequency change step parameters can be set. Because of the phase truncation and DAC happen in the chip, the design add a filter to the DDS chip. The pass-band of the filter is 0-100 M and the decay of the amplitude is steady. And the filter will decay heavily out of the pass-band.2. Complete the design of seven-order elliptic low-pass filter. Use the ATmega128 as the MCU. And I add LCD and buttons to the circuit. The buttons can adjust the frequency to any value between 9M and 11M(the working frequency band is between 10M+100k and 10M-100k), and sweep frequency between the band of very high accuracy. The LCD displays the parameters of signal. So depending on the upper I realize the Human-Computer Interaction.3. Design a measurement system using the ATmega128 chip. Around the two circuit, I use digital and analog power to drive the circuit. Because of the measurement requirement, I use a power adapter to power. But if wanted, it can be powered with battery. With a former signal generator providing signal and latter scope meter I can measure the resonate value of QCM sensor, and I can finish the measurement in my hands, which solves many conditions of QCM measurement and can measure in liquidoid condition.