濕度傳感器和信號(hào)調(diào)理選擇

　　濕度是空氣中水蒸氣量的一個(gè)術(shù)語(yǔ)。相對(duì)濕度（RH）是指在一定溫度下，水蒸氣（空氣和水蒸氣的氣體混合物）的分壓與水的飽和蒸氣壓的比值。因此，簡(jiǎn)單地說(shuō)，RH是空氣在特定溫度下的蒸汽量，與空氣在一定溫度下不凝結(jié)的最大水蒸氣相比。這是天氣預(yù)報(bào)的一個(gè)重要指標(biāo)，因?yàn)樗墙邓⒙端蜢F的可能性的指示器。

　　濕度傳感器的類型

　　濕度傳感器1通常是電容式或電阻式。電容式傳感器比電阻式傳感器具有更線性的響應(yīng)（這些傳感器幾乎具有對(duì)數(shù)響應(yīng)，但在低濕度下靈敏度高）。電容式傳感器在0至100%相對(duì)濕度范圍內(nèi)也可用，電阻元件通常僅限于20至90%相對(duì)濕度。

　　電容式相對(duì)濕度傳感器通常使用經(jīng)過(guò)工業(yè)驗(yàn)證的熱固性聚合物，三層電容結(jié)構(gòu)，鉑電極，除了高溫版本，一些芯片上集成了硅電壓輸出信號(hào)調(diào)理。這些傳感器工作在ΔC或電容變化與濕度水平。交流勵(lì)磁，而不是DC，用來(lái)防止極化

　　Capacitive sensor signal conditioning

　　Multiple circuit architectures may be used with a capacitive humidity sensor. Extra care must be taken during the layout of the pc board in these designs. Any stray capacitance must be minimized in the layout since any added capacitance will act as a parallel capacitance with the sensor and create a measurement error.

　　A careful conformal coating of the pc board and components is advised to prevent unexpected deviations in FOUT of the 555 timers， especially in high humidity conditions.

　　The first and simplest is the capacitance-to-frequency conversion circuit. Figure 1 shows the circuit diagram using theHoneywell HCH-1000 series， a polymer-based sensor with a delta C form factor.