基於非接觸式紅外線溫度感測器單體之新型乾濕球濕度計設計

A Novel Design of Psychrometer Based on a Single-Packaged Contactless Infrared Thermometer

李健(Chien Li) ； 鍾瑞永(Jui-Yung Chung)

《農業工程學報》 63卷2期 (2017/06) Pp. 11-21

https://doi.org/10.29974/JTAE.201706_63(2).0002

摘要

本文提出一個新型乾濕球濕度計的設計，透過一個非接觸式紅外線溫度感測器單體來量測懸掛於空氣流道中濕棉條的溫度來作為濕球溫度，並以感測器單體自身的封裝溫度感測來作為乾球溫度。其中空氣流道透過一個功率為0.35 瓦的微型風扇來進行通風，此紅外線溫度感測器為出廠前已校正且具標準數位通訊介面的小型且低價感測模組。在濕度快速演算部分，推導出飽和蒸氣壓五階多項式近似公式，使得演算能在一般低成本微控制器中快速執行。根據與Goff-Gratch 公式的誤差分析，在0℃~55℃溫度範圍內以此方法得到相對濕度準確度能達到±0.02 以內，相較下一般常用的馬格努斯算式只能達到的±0.1 精度。與基於兩根類比溫度感測棒的傳統乾濕球濕度計比較，本新型設計具有與棉球非接觸及感測器單體同時整合量測乾濕球兩者溫度的能力，帶來更精簡、可靠及易於數位整合的優點。

關鍵字

乾濕球濕度計 ； 濕球 ； 相對溼度 ； 飽和蒸汽壓 ； 紅外線溫度

並列摘要

A novel design of psychrometer is provided, where the air is pumped by a 0.35W mini-fan through a chamber with a hanged wet wick and a single-packaged contactless infrared thermometer aimed at the wick. The thermometer is a small size, low-cost, commercial off-the-shelf and comes factory-calibrated with a digital I^2C communication port, and it can measure both two temperatures of the package itself (dry bulb) and the wick surface (wet bulb). For the fast computation of relative humidity (RH) in a generic microcontroller, a 5^(th)-order polynomial approximation equation for saturation vapor pressure is derived, which makes the calculation can be executed fast on the microcontroller. The error analysis with the Goff-Gratch equations shows that the computational accuracy for RH reading is within ±0.02 compared to ±0.1 of the Magnus approximate form at temperature range 0~55℃. Compared to the conventional architecture of psychrometer based on two analog resistance temperature detectors (RTD), where one of them is soaked in the wet wick. The simple new design based on the contactless and combined temperature measurements has the advantages of compact, reliability, and digital integration.

並列關鍵字

Psychrometer ； Wet-Bulb ； Relative Humidity ； Saturation Vapor Pressure ； Infrared Thermometer