Xiaofeng Meng

Note: A dual-channel sensor for dew point measurement based on quartz crystal microbalance

A new sensor with dual-channel was designed for eliminating the temperature effect on the frequency measurement of the quartz crystal microbalance (QCM) in dew point detection. The sensor uses active temperature control, produces condensation on the surface of QCM, and then detects the dew point. Both the single-channel and the dual-channel methods were conducted based on the device. The measurement error of the single-channel method was less than 0.5 °C at the dew point range of -2 °C-10 °C while the dual-channel was 0.3 °C. The results showed that the dual-channel method was able to eliminate the temperature effect and yield better measurement accuracy.

Dew point fast measurement in organic vapor mixtures using quartz resonant sensor

A fast dew point sensor has been developed for organic vapor mixtures by using the quartz crystal with sensitive circuits. The sensor consists of the quartz crystal and a cooler device. Proactive approach is taken to produce condensation on the surface of the quartz crystal, and it will lead to a change in electrical features of the quartz crystal. The cessation of oscillation was measured because this phenomenon is caused by dew condensation. Such a phenomenon can be used to detect the dew point. This method exploits the high sensitivity of the quartz crystal but without frequency measurement and also retains the stability of the resonant circuit. It is strongly anti-interfered. Its performance was evaluated with acetone-methanol mixtures under different pressures. The results were compared with the dew points predicted from the universal quasi-chemical equation to evaluate the performance of the proposed sensor. Though the maximum deviations of the sensor are less than 1.1 °C, it still has a fast response time with a recovery time of less than 10 s, providing an excellent dehumidifying performance.

Real-time and high accuracy frequency measurements for intermediate frequency narrowband signals

Real-time and accurate measurements of intermediate frequency signals based on microprocessors are difficult due to the computational complexity and limited time constraints. In this paper, a fast and precise methodology based on the sigma-delta modulator is designed and implemented by first generating the twiddle factors using the designed recursive scheme. This scheme requires zero times of multiplications and only half amounts of addition operations by using the discrete Fourier transform (DFT) and the combination of the Rife algorithm and Fourier coefficient interpolation as compared with conventional methods such as DFT and Fast Fourier Transform. Experimentally, when the sampling frequency is 10 MHz, the real-time frequency measurements with intermediate frequency and narrowband signals have a measurement mean squared error of ±2.4 Hz. Furthermore, a single measurement of the whole system only requires approximately 0.3 s to achieve fast iteration, high precision, and less calculation time.

Note: Temperature-frequency calibration method based on spectral analysis for QCR dew point sensor

Each quartz crystal resonator (QCR) shows different frequency behavior as a function of temperature. To get the curve of the temperature effect compensation during the dew-deposition process, we use the active controlled temperature type of the QCR dew point sensor. In this note, a QCR temperature-frequency calibration method based on spectral analysis is described. It combines FFT and spectral refinement and the parameter table method to achieve high precision frequency extraction. Frequency identification accuracy is 10-6. The results showed that the method has a good performance in frequency extraction of the QCR sensors.