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From: scottb@hp-vcd.HP.COM (Scott Bigelow)
Newsgroups: sci.electronics
Subject: Re: Humidity Sensors in Clothes Dryers
Message-ID: <2470018@hp-vcd.HP.COM>
Date: 16 Apr 91 17:16:23 GMT
References: <1991Apr12.113251.16467@minyos.xx.rmit.oz.au>
Organization: Hewlett Packard, Vancouver, WA
Lines: 47

Philips makes a capacitive sensor that I am told is used primarily in clothes
dryers.  Here are some specs:

   Part # 2322 691 90001
   Operating Humidity Range...............10 to 90% R.H.
   Operating Temp. Range..................0 to 85 C
   Capacitance at 25 C, 43% R.H., 100KHz..122pF +/- 15%
   Frequency Range........................1KHz to 1MHz
   Temp. Dependence.......................0.1% R.H./deg C
   Max Voltage............................15V

The capacitance varies from about 110pF to 150 pF as the R.H. increases from 10%
to 90%.  The cost look to be about $5-10 in small quantities.  Philips makes a 
neat booklet on using their sensor which includes app. notes on linearizing the
output, building a humidity controller for a microwave oven, solvency testing,
etc.

    Philips Components
    Airport Road, P.O. Box 760
    Mineral Wells, TX 76067
    TEL (817) 325-7871


There is another sensor that should fill your needs.  This one is a variable
resistance R.H. sensor made by Ohmic Instruments Co.

    Part # UPS-100
    Operating R.H. Range..................10 to 99% R.H.
    Operating Temp. Range.................-20 C to 100 C
    Accuracy..............................+/- 2% R.H., 20% to 80% R.H.
                                          +/- 3% R.H., 10% to 99% R.H.
    Excitation Current....................10 microamps, max
    Temp. Coefficient.....................-0.15% R.H. for 1 deg F change

The resistance varies from about 100Mohms to 20Kohms as the R.H. rises from 10%
to 90%.  The cost is $23.50 each.  An evaluation kit is available for $40.00.

    Ohmic Instruments Co.
    508 August Street
    Easton, MD 21601
    TEL 1-800-626-7713
          301-820-5111


Scott Bigelow
Hewlett-Packard Co., Vancouver Div.
scottb@hp-vcd.vcd.hp.com