行政院農業委員會台南區農業改良場   研究彙報第64號

 

低成本乾濕球濕度計之研製

李健、鍾瑞永、楊清富

摘  要

李健、鍾瑞永、楊清富2014。低成本乾濕球濕度計之研製。臺南區農業改良場研究彙報65:73-86。

  本研究提出一個低成本乾濕球濕度記錄器的設計,將空氣樣本藉由微型風扇抽進流道內,流道內放置一組校正後精度±0.1℃之乾濕球溫度計。溫度計採用低成本且小尺寸的半導體溫度計TMP37,球頭尺寸5x5x4mm3。由於此濕球尺寸遠小於一般PT-100溫度感測探頭,具有反應速度快及水分蒸散量少的優點,亦可搭配0.35W低耗電量微型風扇。採用三階多項式飽和蒸氣壓近似公式,使計算相對濕度及蒸氣壓差的複雜度大幅降低,並且能夠在一般低成本微控制器中快速執行。根據Goff-Gratch公式的誤差分析,以此方法得到相對濕度讀值準確性在15℃~50℃溫度範圍內能達到-0.7~+1.5。記錄器可將資料以指定格式傳送到micro-SD卡作儲存或顯示在文字LCD上,與兩個精確度為±2%之參考感測器相互比較,其相對濕度讀值差異可於約±2%以內,此外並執行溫室環境中的耐久測試。本研究證明低成本及低耗能之高可靠度乾濕球濕度計是可行的,且將可成為未來發展太陽能無線感測網路的基礎技術。

關鍵字:乾濕球濕度計、濕球、相對濕度、飽和蒸氣壓、蒸氣壓差
接受日期:2014年9月26日


A Study on Low Cost Dry/Wet-Bulb Psychrometer

Li, Chien, Jui-Yung Chung and Ching-Fu Yang

Abstract

   A low-cost architecture of psychrometer data logger is provided, where the air sample is pumped by a mini-fan into a channel with a pair of dry/wet-bulb temperature sensors arranged inside with accuracy of ±0.1℃, the wet bulb size is about 5x5x4mm3. The bulb, smaller than the ordinary PT-100 sensor, provides the advantages of fast response and saving water for evaporation; besides, its corresponding mini-fan of 0.35W also provides a low power-hungry solution. Both dry/wet bulb temperatures are used to calculate, with high efficiency, the relative humidity and vapor pressure deficit in a low-cost microcontroller on basis of the 3rd-order polynomial approximation equation for saturation vapor pressure. The error analysis with the Goff-Gratch equations promises that the accuracy for relative humidity reading is within -0.7~+1.5 at 15℃~50℃range. By programming in the microcontroller, the data can be displayed on a text LCD and stored in a micro-SD card with specified format and time interval. Through the comparison test along with calibrated humidity sensor of ±2% accuracy, the difference is within ±2% in relative humidity reading, beside that, a field test in greenhouse is also executed. It proves that this psychrometer, based on the off-the-shelf components, provides cost-effective and reliable performance.

Key words: Psychrometer, Wet Bulb, Relative humidity, Saturation Vapor Pressure
Accepted for publication: September 26, 2014


    回研究彙報目錄