08濕度傳感器系統(tǒng)畢業(yè)論文中英文資料外文翻譯文獻(xiàn)-文庫吧資料
2025-03-11 10:08本頁面
【正文】 ately according to: RH t（ t） =(ES)*(1e )+S Here, the time span 1 is usually very short (typ. 1 – 30 min.), in contrast, the time span 2 is very long (typ. Many hours to days). Here the connection of measurement accuracy and response characteristics bees clear (t until RH=100% is reached). The value at t4 (Fig. 1) is considered to be an exact measured value. However, this assumes that both the humidity and also the temperature remain stable during this entire time, and that the testing waits until this very long measurement time is pleted. These conditions are both very hard to achieve and unusual in practice. For the calibration, there are the following two approaches, which both find use in practice (cf. Fig. 2): measured value at t2 (Fig. 1) is used as a calibration reference. Advantage: ? The required measurement time for reaching the end value (in the example 100%) is clearly shortened,corresponds to practice, and achieves an apparent short response time of the sensor (cf. Fig. 2). Disadvantage: ? If the conditions are similar for a long time (., wet periods in outdoor operation), the sensors exceed the correct end value (in the example 100%) undesirably by up to 10% (cf. Fig. 2). 2. The measured value at t4 (Fig. 1) is used as a calibration reference. Advantage: ? Even for similar conditions over a long time (., wet periods in outdoor operation), an exact measurement result is obtained (cf. Fig. 2). Disadvantage: ? For a humidity jump like in Fig. 1, the sensors very quickly deliver the measured value at t2, but reaching a stable end value (about 36% higher) takes a long time (apparent longer response time)(cf. Fig. 2). In order to take into account both approaches optimally, the measured values at t3 (cf. Fig. 1) are used as the calibration reference by Sensirion AG. 吉林農(nóng)業(yè)大學(xué)本科畢業(yè)設(shè)計 4 Fig. 2: Response characteristics of different humidity measurement systems The housing effect on the response time (2) Here, two types of transport phenomena play a deciding role: ? Convection: For this very fast process, the air, whose humidity is to be determined, is transported to the sensor by means of ventilation. ? Diffusion: This very slow process is determined by the thermal, molecular selfmotion of the water molecules. It occurs even in stationary air (., within a housing), but leads to a long response time. In order to achieve favorable response characteristics in the humidity measurement system, the very fast convection process must be supported by large housing openings and the slow diffusion process mu
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