Journal of Sensor Science and Technology (센서학회지)

The Korean Sensors Society (한국센서학회)
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Effects of Long-term Exposure of High and Low Humidity on Thin-film Humidity Sensors

  • Lee, Sang-Wook (Center for Thermometry and Fluid Flow, Korea Research Institute of Standards and Science) ;
  • Choi, Byung Il (Center for Thermometry and Fluid Flow, Korea Research Institute of Standards and Science) ;
  • Kim, Jong Chul (Center for Thermometry and Fluid Flow, Korea Research Institute of Standards and Science) ;
  • Woo, Sang-Bong (Center for Thermometry and Fluid Flow, Korea Research Institute of Standards and Science)
  • Received : 2018.10.19
  • Accepted : 2018.11.21
  • Published : 2018.11.30
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Abstract

The effects of long-term exposure of high and low humidity on thin-film humidity sensors are investigated. Five commercially available thin-film humidity sensors are initially calibrated in a humidity chamber as a reference before longterm exposure to high and low humidity. Then, the sensors are kept in a high-humidity environment (~95 %rh) for four months. After the exposure, the sensors are calibrated in the same manner as the initial calibration. Consequently, the device reading values from the humidity sensors are elevated up to about 5 %rh. Interestingly, the degree of elevation by the high-humidity exposure shows a negative correlation with the price of the humidity sensors. Humidity sensors are then kept in a low-humidity environment (~10 %rh) for another four months. After the exposure, a calibration similar to the initial calibration is performed. As a result, the device reading from humidity sensors is decreased, indicating a recovery from the effect of high-humidity exposure. The durability test conducted in this study provides experimental evidence for the use of thin-film humidity sensors in high-humidity environments such as greenhouses and food factories for a long period of time.

Keywords

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Fig. 1. Initial calibration of five thin-film humidity sensors from different manufacturers before exposure to high and low humidity.

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Fig. 2. Exposure of humidity sensors to high humidity (~95 %rh) in water chamber for four months.

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Fig. 4. Increase of device reading values of humidity sensors after long-term exposure to high humidity as a function of reference relative humidity.

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Fig. 5. Increase in device reading values of humidity sensors after long-term exposure to high humidity as a function of device price.

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Fig. 6. Exposure of humidity sensors to low humidity (~10 %rh) in descant chamber for four months.

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Fig. 8. Increase of device reading values of humidity sensors after long-term exposure to (a) high humidity followed by (b) low humidity as a function of reference relative humidity. Dashed rectangular boxes indicate 2 %rh variations from initial calibration.

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Fig. 3. (a)-(e) Device reading values of humidity sensors (A-E, respectively) as a function of reference relative humidity before (black square) and after (blue circle) long-term exposure to high humidity.

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Fig. 7. (a)-(d) Device reading values of humidity sensors (A-D, respectively) as a function of reference relative humidity before (black square) and after (blue circle) long-term exposure to high humidity, and after (red triangle) long-term exposure to low humidity.

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