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help! humidity sensor — Parallax Forums

help! humidity sensor

ArchiverArchiver Posts: 46,084
edited 2001-02-24 03:43 in General Discussion
i need to build a humidity sensor, and i am fairly inept at circuits...i
have access to a hih-3610 humidity sensor, so i would like to use this, but
do not need to. i need help designing the circuit to implement the sensor
(and writing the code) if anyone has a quick and easy solution for me, i
would like to hear it.

bill
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Comments

  • ArchiverArchiver Posts: 46,084
    edited 2001-02-22 22:29
    Hi,

    I have been trying the same type of thing: Are you measuring relative
    humidity or absolute humidity?

    Thanks,
    Corey.



    --- In basicstamps@y..., "William Frost" <william_frost@h...> wrote:
    > i need to build a humidity sensor, and i am fairly inept at
    circuits...i
    > have access to a hih-3610 humidity sensor, so i would like to use
    this, but
    > do not need to. i need help designing the circuit to implement the
    sensor
    > (and writing the code) if anyone has a quick and easy solution for
    me, i
    > would like to hear it.
    >
    > bill
    > _________________________________________________________________
    > Get your FREE download of MSN Explorer at http://explorer.msn.com
  • ArchiverArchiver Posts: 46,084
    edited 2001-02-23 01:30
    I've always thought that humidity measurement was relative. How would you
    measure absolute humidity?

    Original Message
    From: <the_coin_guy@y...>
    To: <basicstamps@yahoogroups.com>
    Sent: Thursday, February 22, 2001 5:29 PM
    Subject: [noparse][[/noparse]basicstamps] Re: help! humidity sensor


    > Hi,
    >
    > I have been trying the same type of thing: Are you measuring relative
    > humidity or absolute humidity?
    >
    > Thanks,
    > Corey.
    >
    >
    >
    > --- In basicstamps@y..., "William Frost" <william_frost@h...> wrote:
    > > i need to build a humidity sensor, and i am fairly inept at
    > circuits...i
    > > have access to a hih-3610 humidity sensor, so i would like to use
    > this, but
    > > do not need to. i need help designing the circuit to implement the
    > sensor
    > > (and writing the code) if anyone has a quick and easy solution for
    > me, i
    > > would like to hear it.
    > >
    > > bill
    > > _________________________________________________________________
    > > Get your FREE download of MSN Explorer at http://explorer.msn.com
    >
    >
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2001-02-23 17:07
    >
    >I've always thought that humidity measurement was relative. How would you
    >measure absolute humidity?
    >

    "Humidity" can be expressed in relative or in absolute terms. Example
    measures of absolute humidity would be vapor density (grams of water vapor
    per cubic meter of air) or as vapor pressure (the partial pressure exerted
    by the water vapor in the air). Relative humidity is a dimensionless ratio
    of, for example, the actual vapor pressure of the air divided by the
    maximum vapor pressure which could be contained in the same air at the air
    temperature. Some sensors (based on their operating principle) inherently
    respond to relative humidity, and others respond to absolute humidity.

    Note that a relative humidity sensor tells you nothing about how much water
    vapor is actually present in the air you are sampling. If you need absolute
    humidity, and are using a relative humidity sensor, then you need to also
    measure the air temperature immediately adjacent to your relative humidity
    sensor. You then calculate the absolute humidity using the temperature and
    the definition of relative humidity mentioned above.

    I may be mistaken, but the hih-3610 part number sounds like a HyCal
    relative humidity sensor part number. You might check out their web site at:
    www.hycalnet.com and do a search for hih-3610

    Hope this clarifies things a bit.

    Steve
    Steve Roberts: sroberts@s...
  • ArchiverArchiver Posts: 46,084
    edited 2001-02-24 03:43
    An accurate and customary way to measure humidity is to measure the air
    temperature and the dew point (temperature). With these two numbers then
    you consult a look-up table or run the math. The Weather Service does it
    that way
    because the dew point temperature is very valuable number. In aviation, as
    the two temps get close, watch out for icing even though the temp is well
    above freezing.

    Measuring the air temp' is easy. The dew point is more fun and should be a
    great little stamp project. One way that it is done is to shine a light
    source on a small mirror and look at the reflection with a detector- Then
    using a thermoelectric cooler (peltier junction) slowly cool the mirror
    until moisture condenses on it, (fogs it up) and spoils the clear
    reflection. The photo sensor sees the light decrease and alerts your stamp
    program to read the dew point temperature of the mirror. Now do your
    look-up or math- Commercial versions do just that, repeating the cycle
    every few minutes. A simple scheme with no chemistry, but you do have to
    keep things clean and keep fresh air moving thru the system while
    protecting it from weather.


    Wayne Roderick P.E. (EE, ret)
    CEO, Teton Short Line, (NMRA life-1721)
    e-mail tetonsl@i... Pocatello Idaho, USA
    http://www.ida.net/users/tetonsl/railroad
    Note new URL- /biz/ becomes /users/
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