Years ago I had to deal with this and the instruments and sensors we used matched well against dry and wet bulb measurements. I suspect consumer level stuff varies considerably in reliability and accuracy.
The capacitive sensors are tricky to use because they require AC excitation to prevent damage from electromigration. I see a lot of integrated sensors are available now and I wonder how well they really work On Fri, 28 Oct 2016 09:39:04 +1100, you wrote: >You are correct to question commercial humidity sensors. >It seems to have come about because no-one can make a dollar by selling >humidity. >Manufacturers do not tell the truth, they think ours is as good as theirs so >we >should claim the same accuracy. People buy these sensors, believe them, and >buy more. > >It is not hard to measure humidity/temperature. (they should be measured >together). >Cover the bulb of an ASTM32C thermometer with cotton gauze. Insert it through >the wall > of a short length (18) of 4 metal tube, insert another ASTM32C thermometer > through the side >of the tube 4 upstream. Put a computer fan on the outlet of the tube sucking >air over >the thermometer bulbs at about 4m/s. Wet the thermometer bulb, but NEVER touch >it with your fingers. >In about 3 minutes you can take two temperature readings. There are a number >of tables and calculation methods, >some much worse that others that will convert these values to air temperature, >Relative humidity, >Dew Point temperature etc. You get accuracy of 1% from temperatures measured >to 0.1C. >If anyone is interested I have basic routines for XCEL spreadsheet use to do >the hard work. >This is based on the WMO Reference Psychrometer developed by Russel Wylie of >NML Australia. > >> On 28 Oct 2016, at 12:43 AM, Ron Bean <[email protected]> wrote: >> >> And since this is time-nuts: Measuring humidity accurately is tricky. >> According to people who have tested them, commercial electronic humidity >> sensors, when tested in a lab, have never come anywhere close to the >> accuracy claimed in the data sheet. The best you can hope for is >> consistent readings, not absolute accuracy. >> >> ... _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
