Design and Accuracy Improvement of Organic Gases Monitor for Cultural Relics Protection

An organic gases instrument for monitoring of volatile organic gases in museum is presented. The key technologies of the monitor are the quartz crystal gases sensor and the frequency measurement. The sensor platform employs quartz crystal resonator as the base, using a direct current plating technology to plate polyaniline film on the one of the electrodes. Since the organic gases concentration is converted to the frequency fluctuation of the quartz crystal gases sensor, the detection accuracy is decided by the frequency measurement accuracy. There are three key factors leading to low accuracy. They are time base error, triggering error and quantization error. The temperature compensated crystal resonator is applied as reference frequency signal source in order to reduce the time base error. The 16-bit high-speed MCU and high-speed CMOS chips are employed to reduce the triggering error. Compared with the equal precision frequency measurement method, the accuracy of the monitor can be improved two orders of magnitude with the application of the complete synchronous frequency measurement method. The accuracy of the monitor can be greatly improved through these methods and the perfect solutions are demonstrated as emphases in this paper.