Humidity sensor is +/-3% accurate

There is a nice article in ECN magazine by Valerie Rothermel-Nelson from Honeywell regarding small accurate humidity sensors. These sensors are only 4×10mm. Price is $20 in 1000s and 30 ea in a 5-pack sampler, both are suggested resale. (I had to call Honeywell, ECN did not have pricing, but EDN insists on pricing) I remember when there were two ways to get decent humidity readings. One was a dew point sensor with a little mirror and refrigerator so you could see what temperature the mirror fogged up and infer humidity. The other was this abominable gizmo with horsehair in it. The horsehair would shrink with high humidity and that is how the senor inferred humidity. Oh, I forgot, there was the whole wet-bulb thing where you moistened a thermometer bulb and spun it around you on a 5-foot rope. That was not too practical for an electronics application. So I am always interested when I see a humidity sensor.

The Honeywell humidity sensor uses a thermoset plastic capacitor that must change value with humidity. They only draw 200uA. The HIH-4030 series can come as tight as 2% over a limited range. Interchangeability is +/-5%. The HIH-4030/31 datasheet is online (pdf).