Dew Point Calibration System Using a Quartz Crystal Sensor with a Differential Frequency Method.

Ningning Lin,Jing Nie,Xiaofeng Meng

doi:10.3390/s16111944

Abstract

In this paper, the influence of temperature on quartz crystal microbalance (QCM) sensor response during dew point calibration is investigated. The aim is to present a compensation method to eliminate temperature impact on frequency acquisition. A new sensitive structure is proposed with double QCMs. One is kept in contact with the environment, whereas the other is not exposed to the atmosphere. There is a thermal conductivity silicone pad between each crystal and a refrigeration device to keep a uniform temperature condition. A differential frequency method is described in detail and is applied to calibrate the frequency characteristics of QCM at the dew point of −3.75 °C. It is worth noting that frequency changes of two QCMs were approximately opposite when temperature conditions were changed simultaneously. The results from continuous experiments show that the frequencies of two QCMs as the dew point moment was reached have strong consistency and high repeatability, leading to the conclusion that the sensitive structure can calibrate dew points with high reliability.

Highlights

Precision monitoring on ambient humidity plays a crucial role in myriad automatic production such as in electronics, machinery, agriculture, pharmacy, and storage [1]
The most popular mass sensor, known as a quartz crystal microbalance (QCM), is a very stable and sensitive device, and its applications have extended to biochemistry, environmental monitoring, explosives detection, and intrusion detection [11,12,13]
Unlike mounting a copper metallic O-ring [15] or spring [29], two circles of thermal conductive silicone pads are stuck along the outer edge of the PT100 sensors, and the outer edge of the dual quartz crystal microbalance (DQCM) is bonded to the thermal conductive silicone pads to seal the lower surface, which benefits the uniformity of the heat transfer and shortens the response time of the dew point

Summary

Introduction

Precision monitoring on ambient humidity plays a crucial role in myriad automatic production such as in electronics, machinery, agriculture, pharmacy, and storage [1]. One of the potential problems about QCM-based sensors is their cross sensitivity to thermal fluctuations, which can seriously compromise sensor accuracy [18,19,20,21]. It is a common issue in applications where the QCM is used for in situ sensor measurements in dynamically variable environments [21,22], where the sensor often operates over a wide temperature range. Temperature has become an important error source in the process of dew point calibration

Objectives

Methods

Results

Conclusion