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Handbook of air conditioning and refrigeration / Shan K

Handbook of air conditioning and refrigeration / Shan K

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2.18 CHAPTER TWO<br />

FIGURE 2.7 Ion-exchange resistance-type electric hygrometer. (a)<br />

Front <strong>and</strong> side view <strong>of</strong> sensor; (b) characteristic curve <strong>of</strong> R versus �.<br />

(Reprinted by permission <strong>of</strong> General Eastern Instruments.)<br />

inside a capsule. The golden electrodes <strong>and</strong> the dividing plastic foil form a capacitor. Water vapor<br />

penetrates the gold layer, which is affected by the vapor pressure <strong>of</strong> the ambient <strong>air</strong> <strong>and</strong>, therefore,<br />

the ambient relative humidity. The number <strong>of</strong> water molecules absorbed on the plastic foil determines<br />

the capacitance <strong>and</strong> the resistance between the electrodes.

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