AN-256Circuitry for Inexpensive Relative Humidity …
ApplicationReportSNOA720B August1981 ,humidityis ,albeithighlyaccurate,arenotobviousandte ndtobeexpensiveandcomplex(SeeBox).Accura tehumiditymeasurementis vitaltoa numberofdiverseareas,includingfoodproces sing,paperandlumberproduction, , August1981 RevisedMay2013AN-256CircuitryforInexpens iveRelativeHumidityMeasurementSubmitDocu mentationFeedbackCopyright 1981 2013, ,thesensordescribedbytheresponsecurve(Fi gure1) isinexpensiveandprovidesa furtherconsiderationin signalconditioningis ,it hasa C a chemicallytreatedstyrenecopolymerthathas a atitssurface,timeresponseis reasonablyrapidandis blockdiagramoftheconceptchosentoinstrume ntthesensorappearsin Figure2. Anamplitudestabilizedsquarewavethatis symmetricalaboutzerovoltsis usedtoprovidea precisionalternatingcurrentthroughthesen sor,satisfyingtherequirementfora fedintoa currentsensitive(forexample,theinputis atvirtualground)logarithmicamplifier, scaled,rectifiedandfilteredtoprovidea 40%is compensatedbybreakpointtechniquesin Figure3.
Circuitry for Inexpensive Relative Humidity Measurement www.ti.com 1 Circuitry for Inexpensive Relative Humidity Measurement Although not as accurate as other methods, the sensor described by the response curve (Figure 1) is
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