Uncertainly Analysis of Two Types of Humidity Sensors by a Humidity Generator with a Divided-Flow System

Abstract

Humidity measurement is an important technique for the agricultural, foods, pharmaceuticals, and chemical industries. For the sake of convenience, electrical relative humidity (RH) sensors have been widely used. These sensors need to be calibrated to ensure their accuracy and the uncertainty measurement of these sensors has become a major concern. In this study, a self-made divided-flow generator was established to calibrate two types of electrical humidity sensors. The standard reference humidity was calculated from dew-point temperature and air dry-bulb temperature measured by a chilled mirror monitor. This divided-flow generator could produce consistent result of RH measurement results. The uncertainty of the reference standard increased with the increase of RH values. The combined uncertainty with the adequate calibration equations were ranged from 0.82% to 1.45% RH for resistive humidity sensors and 0.63% to 1.4% for capacitive humidity sensors, respectively. This self-made, divided-flow generator, and calibration method are cheap, time-saving, and easy to be used. Thus, the proposed approach can easily be applied in research laboratories.

Calibration of hygrometers at non-static conditions

“…The estimated expanded uncertainty (k = 2) of the nonstatic calibration at 50 %rh and 25 °C was 0.6 %rh and 1.2 %rh when using a chilled mirror hygrometer and a capacitive humidity sensor as a reference, respectively. This is at the same level as typically reported for reference hygrometerbased relative humidity calibration systems applying a static calibration procedure [8][9][10][11][12][13][14]. Tables 2 and 3 indicate an excess of 0.19 %rh and 0.03 %rh in expanded uncertainty due to the non-static procedure when using a chilled mirror hygrometer and a capacitive humidity sensor as a reference, respectively.…”

Uncertainty Analysis of Polymer-Based Capacitive Relative Humidity Sensor at Negative Temperatures and Low Humidity Levels

“…The two-flow method is based on controlling the ratio of flow rates of two gaseous mixtures [20,21]. One stream is dry air, while the other stream is saturated air with water.…”