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One of the difficulties in measurements of relative humidity in a variety of environments is temperature-dependence especially at cold temperatures. Here, we report on the reduction and the compensation of temperature effects on humidity measurements using dual humidity sensors based on quartz crystal microbalance (QCM). Graphene oxide film is coated on quartz crystals as a humidity sensing layer for the detection of water sorption by the change of resonance frequency. Relative humidity in a test chamber, where dual QCM humidity sensors are located, is precisely controlled using a humidity generator at the temperature range from 20 °C to −60 °C. It is found that single QCM humidity sensors measure humidity significantly higher than reference relative humidity by the generator as temperature is lowered due to the temperature-dependent resonance of quartz crystals. In an attempt to cancel out the temperature-dependent oscillation of QCM sensors, the ratio of resonance frequencies of dual QCM humidity sensors is used. Consequently, temperature-dependent errors in humidity measurement at low temperatures are evidently reduced. For the compensation of the remaining errors in the humidity measurement by dual QCM humidity sensors, a single formula is empirically obtained. After the compensation of low temperature effects, the dual QCM humidity sensors provide the measurement capability in terms of residual errors less than 1.1%rh throughout temperatures from 20 °C to −60 °C. This study provides a useful insight to extend the applicability of QCM-based humidity sensors to environments with cold temperatures.

A new saturator-based low frost-point generator (LFPG 2) is developed at the Korea Research Institute of Standards and Science (KRISS), and its uncertainty is evaluated from 7 nmol‧mol-1 to 1000 nmol‧mol-1 in nitrogen. The humidity generator operates in the two-temperature two-pressure mode to achieve target water vapor concentrations. First, the apparatus of the generator and the operation procedures, including purging mode and generation mode, are introduced in depth. Then, all uncertainty factors that affect trace-moisture generations are analyzed using a hygrometer based on cavity-ring down spectroscopy. Consequently, the expanded relative uncertainties in the range of (7 – 1000) nmol‧mol-1 are 4.9% – 0.8% at a coverage factor of k = 2, respectively. It is found that the effect of water adsorption/desorption is significantly reduced with compact design and sufficient purging. Thus, the uncertainty of the generator is enhanced compared with trace-moisture standards in other national metrology institutes including the KRISS LFPG 1. Finally, the time scales of humidity generations for various flow rates are investigated for efficient calibration of the hygrometers.

One of the challenges in temperature measurements in the upper air using a radiosonde is the correction of solar radiation effects. A prerequisite for the correction is in situ measurements of solar radiation. In this study, a new technique for the measurement of solar irradiation followed by the temperature correction was developed using dual temperature sensors with different emissivities. The principle is that the radiation intensity is calculated by using the temperature difference between two thermistors coated with different materials (one with graphite and the other with aluminium) and then the irradiance obtained is used for the correction. As a first stage, the effect of air pressure on the temperature correction process using dual thermistors was examined. The temperature difference between the two sensors was found to be linearly proportional only to the irradiance up to 360 W m−2, regardless of air pressure from 10 to 1000 hPa at room temperature. This provides a way to calculate the irradiance by simply measuring the temperature difference between the two sensors. The calculated irradiance showed a difference of less than 45 W m−2 (13% of the maximum irradiance) compared to the irradiance measured with a calibrated pyranometer. The extended uncertainty of the calculated irradiance was 53.5 W m−2 (coverage factor k = 2). A reference temperature sensor in the shade was used to obtain a correction formula as a function of air pressure and calculated irradiance. When the temperature was corrected using the calculated irradiance, the extended uncertainty of the corrected temperature was 0.98 K (k = 2).

Accurate measurements of temperature and water vapor in the upper-air are of great interest in relation to weather prediction and climate change. Those measurements are mostly conducted using radiosondes equipped with a variety of sensors that are flown by a balloon up to lower stratosphere. Reference Upper Air Network (GRUAN) has identified water vapor pressure as one of the most important measurands and has set an accuracy requirement of 2 % in terms of the mixing ratio. In order to achieve the requirement, many errors in the humidity measurement such as a temperature dependency in sensing characteristics including measurement values and response time need to be corrected because humidity sensors of radiosondes pass through low-pressure (1 kPa) and low-temperature (−80 ∘C) environments in the upper-air. In this paper, the humidity sensing characteristics of Jinyang radiosonde sensors in relation to temperature dependencies were evaluated at low temperature using a newly developed ultralow-temperature humidity chamber. The sensitivity characteristic curve of the radiosonde sensors was evaluated down to −80 ∘C, and the calibration curves of the humidity sensor and the temperature sensor were obtained. The response time of humidity sensor slowly increased from 52 to 116 s at the temperature from 20 to −40 ∘C, respectively, and then rapidly increased to almost one hour at −80 ∘C. Those results will help to improve the reliability of the upper-air observation data.

We study the sorption/desorption hysteresis of thin-film humidity sensors using graphene oxide (GO) and amine-modified GO (GO-NH 2 ) as sensing materials for relative humidity (%RH in unit) based on capacitance and conductance measurements. GO sensors present a lower level of hysteresis-induced errors in both capacitance (3.1 ± 0.5%RH) and conductance (2.2 ± 0.2%RH) measurements in the humidity range from 5%RH to 95%RH at 25 °C, whereas GO-NH 2 sensors show a higher degree of hysteresis, resulting in errors of 5.9 ± 1.0%RH and 7.9 ± 0.4%RH by capacitance and conductance measurements, respectively. We discuss a possible mechanism behind the hysteretic behavior of these sensors based on molecular compositions and their interactions with water molecules by using Fourier transform infrared (FT-IR) spectroscopy and by elevating the experimental temperature, respectively. We find the hysteresis-induced errors present a trade-off relationship with the sensitivity between these sensors, emphasizing the importance of studying the sorption/desorption hysteresis as an essential factor in the development of humidity sensors.

Although a protective cap on the humidity sensor of radiosondes is an effective tool to prevent the sensor from wetting by rain and/or clouds, the cap is thought to be responsible for poor ventilation and thereby induces a time delay in the measurement of relative humidity in upper air. In the present study, a new type of the protective cap having a double cap configuration has been developed for improving the ventilation of air. The double cap consists of an outer cap and an inner cap with holes and windows on the top and sides of each cap, respectively, that are designed not to face each other, between two caps for blocking the penetration of water droplets. The wetting of the double cap was tested by artificial water droplets as well as during flying tests on rainy days and the humidity sensor in a double cap was not wet in both cases. In addition, the response of sensors to indoor humidity changes as well as during balloon-borne measurements was found to be faster in the case of double caps than conventional closed caps, suggesting the enhancement of ventilation when using the double cap. The present study provides an efficient way to improve the performance of humidity sensors of radiosondes by simply modifying the design of protective caps.

One of the prerequisites for accurate measurements of relative humidity using thin-film humidity sensors is to obtain a single calibration equation that can be effectively applicable to individual sensors even at different temperatures. Here, we report on a normalization methodology in order to reduce difference among sensor units and also temperature dependency of humidity sensors based on quartz crystal microbalance (QCM). Three independent QCM humidity sensors using graphene oxide (GO) as a humidity sensing material are fabricated from a same batch of GO solution. Frequency shifts of these sensors upon humidity changes from 10 %rh to 90 %rh at 20 °C are normalized to minimize measurement errors occurring due to fabrication tolerance among sensors. It is demonstrated that the maximum measurement error of three sensors is reduced from 4.83 %rh to 1.66 %rh after using a normalized calibration equation. The normalization methodology is then extended to humidity measurements at different temperatures (10 °C and 30 °C). It is found that the normalized frequency shifts of GO-based QCM humidity sensors are consistent at different temperatures. The maximum measurement error due to temperature dependence of these sensors is reduced from about 5.60 %rh to 2.53 %rh after using normalized frequency shifts for a calibration equation. The same normalized calibration equation is applicable to a faulty sensor with smaller frequency shifts within the same budget of the maximum measurement error (2.53 %rh). The normalization methodology using GO-based QCM humidity sensors will provide an economical calibration process because it requires only two humidity points.

The KRISS low frost-point humidity generator which has been operated by the two-temperature method in the frost-point range from $$-95\,^{\circ }\hbox {C}$$ to $$-40\,^{\circ }\hbox {C}$$ since 2006 is reformed to a two-temperature, two-pressure type, in order to extend the calibration capability to a frost point of $$-105\,^{\circ }\hbox {C}$$ . The temperature and pressure of the saturator were controlled to $$-95\,^{\circ }\hbox {C}$$ and 1 MPa, respectively. The water-vapor mole ratio generated by the upgraded humidity generator reached $$4\,\hbox {nmol}{\cdot }\hbox {mol}^{-1}$$ . The uncertainty of the generator was estimated by calculations as well as a series of experiments including the stability of the generated frost point, the saturation efficiency with a varied gas flow rate, and the change of water-vapor mole ratio in the tubing line. The standard uncertainty of the generator is less than $$0.09\,^{\circ }\hbox {C}$$ at the frost point of $$-95\,^{\circ }\hbox {C}$$ and is increased to $$0.19\,^{\circ }\hbox {C}$$ at the frost point of $$-105\,^{\circ }\hbox {C}$$ . The increase in uncertainty is mainly due to the water adsorption/desorption on the internal surface of tubing from the saturator to the hygrometer.

As the next-generation flexible display elements are very vulnerable to moisture, securing proper encapsulation is a decisive factor in enabling a long working life. Therefore, together with the recent development of plastic barrier films with very low permeabilities, interest in the permeabilities of sealants used for perimetric sealing has been increasing. In this study, equipment with a resolution of approximately ∼10−7 g·day−1 to measure moisture permeability in perimetric sealing was established, and the permeabilities of different sealants were measured. This equipment could have applications not only in the display industry but also in other sectors requiring encapsulation technology, such as the semiconductor and solar cell industries.

We have investigated temperature dependence and long-term change of humidity measurement from 32 relative humidity sensors. Thereadings of the humidity sensors depended not only the reference humidity, but also temperature of the chamber. Approximately, thetemperature dependence of the humidity sensor in average was 0.05 %R.H./°C in the temperature range from 5°C to 55°C. For humid itysensors that have an internal temperature compensation circuit, the resulting temperature dependence was weaker by 20%. It should bealso noted that for the humidity sensors used in this work underwent ae 3 %R.H. change per year for level of confidence of 95%. Theusers of relative humidity sensors may refer this value as a minimum change when they set the calibration interval of the humiditysensors. Keywords : Humidity sensor, Temperature dependence, Long-term change 1. « E I  ° A I œ ¬  O O A · « E I° ? µ « µ ‘ a “ ¬˜. U ? µ « ¯ § ‘ œ « E « ¤  ° ” ‹ „ ’  a „ ˜ . A I o ° ? µ ¯ § asœ © °  A A I « I ÷ ¬ ‡ ? µ E ¬ ¯ § ¯ AE ° U ¸ ‘I AE ¸ ¸ – ’ ÷ ˜ [1-3]. ¯ AE ° € A ¬ ÷’ , I – « E I ? «¸ ‘ O A ¬ µ « O °µ ‘a “ ¬˜[4,5]. œ I – « ? µ E ¶ A ° ¶ ¯ œ ¬ U ° ¬ « ¬ µ ° 20-25 C A A« „ ¬ µ ° § ’ § §AE µ€ A O ¶ ¯ œ I ¬ µ O ° I „ § ¶ ‡ o ¶ ¯ y ÷ I ÷ I « § A ˜ . « , § ‘ ¸ ° ‡ ? µ E « ? µ ¯ § § O I £ « AE ¶ O – – œ © « ¬ µ ° 20-25 C– ˜ « „ ¬ µ ° ‚œ© § ¶ ” ‚œI ÷ ˜ . ¬ µ« ° I „ E  ‰ µ 10-40 C A a « o ¬ µ £ a ° ¯ § œ ¬ O – I « O ÷ ˜ [6]. O ’  ° ? µ E ¬˜ A „ ¬ µ ¸ s ° A I « I ÷ ˜ .˜ € A I¬ µ ° ? µ ¶ ¯ § œ © 25 C – ˜ ° ¯ § „ § « § ’ a I œ E ´ I ° ”  ÷’ A I ‡ ° ¬ A ° I „ § ° A i AE ÷ ˜ . a ¨ ¬ ‡ ? µ E «? µ § ’ « ¬ µ O ae« E ‘ O ¶ † « œ © I E – AE „ O – , A ¬  ° « § AE „ ? µ ¯ § € A O ‡ ‘ U ° µ U A ƒ O A ˜ .2. « E E a « E ° A I » ‘ y  O ¬ ¬ ? (? µ » § µ : ae 0.5%R.H. ¬ µ » § µ : ae 0.1 C)O ? µ ¶ O ¯ § œ ‘ s „ I °? µ E (I ° ¬ µ AE   AE µ (k=2): 0.19 C D.P.)A ˜ . Fig. 1 ?µ § ’ « ¬ µ µ ‘ U ° ° A I » ¯ §  ° A ˜ . a ¨ ° ¬‡ ? µ E « ¬ µ µ ‘ U ° ¶ s ÷ – œ « I E ° ? µ ¯ § ° A A I œ ¬ ¬ ? µ ‘ œ E ¶ ” ° œ © « Eœ¥ ˜ .Table 1° ¬ A ¨ ° A I » ? µ E O § ¨ µ ° € ¶ © ÷ I ÷ ˜ . ? µ E ¬ µ AE A † ’ „ ¤ ‡ O ‡ „ ‡ AE« I O ¯ £ ¶ AE ¬ O – I œ ¥ ˜ . µ AE A † ’ ¶ ¤ A ¶ U

The KRISS low frost-point humidity generator (LFPG), was developed in 2006 for the frost-point range (−95 to −40)°C in order to extend calibration capabilities. In this paper, the evaluation of the generator’s uncertainty budget is reported for which each uncertainty component was categorized and estimated by experiment and calculation. The uncertainty of the LFPG depends on the generated frost point, gas flow rate, and change of moisture concentration in transportation. The standard uncertainty of LFPG is less than 32 mK in the frost-point range from −70 °C to −40 °C. However, in the lower frost-point range, the uncertainty increases to 137 mK at −90 °C, and this is mainly due to water adsorption or desorption in the transportation tubing from saturator to hygrometer.

Specific surface area is becoming a very important factor when newly developed advanced nano-materials are evaluated. But there have been many differences in results when measuring specific surface areas, depending on the measuring equipments and analysis method. To verify the reliability of the specific surface area measurement device supplied within the country, Round Robin Test (RRT) has been done at 21 affiliated research institutes. As a result, it was found that several institute had problems in measuring of gas adsorption amount in measuring equipment, and this proved the need for certified reference material (CRM). Furthermore, it was also found that the results from BET analysis is easily swayed by the analyst`s subjectivism, and the calculated results may differ up to 16% in case of CRM I depending on the selection range of BET analysis. So this showed that a standard guideline for BET constant C value and fitting correlation coefficient R is needed, to properly select range in BET analysis. The experience in RRT, distribution of CRM, and standardized procedure would result in improved reliability in industrial processes, and thus, would contribute to the quality management, the productivity improvement, the safety evaluation, and the new material development.

As organic light-emitting diodes (OLEDs) and other optoelectronic materials are very vulnerable to moisture and oxygen, securing proper encapsulation is critical in the development of flexible OLED displays and other flexible electronic devices. This problem is typically solved by the use of barrier-coated polymeric films that are composed of alternating organic/inorganic multilayers. Precision devices testing for water vapor permeability in ultra-low range were developed in KRISS using water containing tritium. These devices are under operation to measure the range covering (10−7 to 10−2) g·m−2·day−1. In this study, various studies on water vapor permeability through barrier-coated flexible films were conducted with varying temperature and humidity, and it was observed that effects of temperature and humidity were significant. Permeability was increased a few hundred times and 15 times when increasing temperature from 23 to 80°C, and relative humidity (rh) from 6 to 72% rh, respectively. These results can provide valuable information on the reliability evaluation of flexible electronics products.