s882823@minyos.xx.rmit.oz.au (Scott Reynolds [.../* sbr */...]) (04/12/91)
I have a question hopefully someone out there in net-land can answer? We (a group of 17 Electronic Eng 3rd Year Students) have a 12 week design project for designing a Micro Controller for a domestic clothes dryer. After extensive market research (looking in the local dept. store) found that humidity controlled dryers were rare - hence our desire to use the exhaust air humidity as a indication of the dryness. The problem arises as to selecting an appropriate sensor, considering the nasty environ. Does anyone know of sensors used in commerically availiable products Any suggestions/reply would benefit 17 frustrated Eng Students (and probably give 'em a better mark too!!!!!!!) Thanks Scott Reynolds 4th Year Electronic Eng/Computer Sci. Student RMIT Aust.
bew4568@summa.tamu.edu (WILSON, BRUCE ERIC) (04/13/91)
In article <1991Apr12.113251.16467@minyos.xx.rmit.oz.au>, s882823@minyos.xx.rmit.oz.au (Scott Reynolds [.../* sbr */...]) writes... >I have a question hopefully someone out there in net-land can answer? > >We (a group of 17 Electronic Eng 3rd Year Students) have a 12 week >design project for designing a Micro Controller for a domestic >clothes dryer. After extensive market research (looking in the >local dept. store) found that humidity controlled dryers were >rare - hence our desire to use the exhaust air humidity as a indication >of the dryness. > The problem arises as to selecting an appropriate sensor, considering > the nasty environ. > Does anyone know of sensors used in commerically availiable products > > > Any suggestions/reply would benefit 17 frustrated Eng Students > (and probably give 'em a better mark too!!!!!!!) > > Thanks > > Scott Reynolds > 4th Year Electronic Eng/Computer Sci. Student RMIT Aust. Well, a dryer that mon and dad had 10 years ago had 2 contacts on the back wall of the tumbler. I suppose the contacts were sufficiently conductive with wet clothing, and the timer (mechanical) was prevented from advancing. When the clothes were dry to some extent the timer continued for a fixed period, to make sure everything got dry. The sensors were rather elongated, and sloped away from the rear wall (in the direction of rotation, that is) to keep a good contact with the cloths. | |______ | // | // Back wall---->| //<--- Sensor strips (2, one above the other) | // | // Rotation | // Direction | |// | |/ \/ Bruce
jeff@hpuplca.nsr.hp.com ( Jeff Gruszynski ) (04/13/91)
* / hpuplca:sci.electronics / s882823@minyos.xx.rmit.oz.au (Scott Reynolds [.../* sbr */...]) / 4:32 am Apr 12, 1991 / * I have a question hopefully someone out there in net-land can answer? * * We (a group of 17 Electronic Eng 3rd Year Students) have a 12 week * design project for designing a Micro Controller for a domestic * clothes dryer. After extensive market research (looking in the * local dept. store) found that humidity controlled dryers were * rare - hence our desire to use the exhaust air humidity as a indication * of the dryness. * The problem arises as to selecting an appropriate sensor, considering * the nasty environ. * Does anyone know of sensors used in commerically availiable products * * * Any suggestions/reply would benefit 17 frustrated Eng Students * (and probably give 'em a better mark too!!!!!!!) * * Thanks * * Scott Reynolds * 4th Year Electronic Eng/Computer Sci. Student RMIT Aust. * ---------- I would strongly recommend using Thomas Catalog for this search. It's available at most libraries. A set of green monstrosities! Look under Humidity Sensors. I know there's a company called 'Omega <something or other>' (not, apparently, related to the thermocouple people in Conn.) that makes them. Somewhat pricey, ~$30/sensor, with each sensor only giving about 15-20% RH range. Not spectacular dynamic range. They can be poisoned fairly easily by things like sulfur compounds and liquid water. There are special ($) teflon coated versions. Last I talked to them they accepted only POs or CODs. Jeff Gruszynski Santa Clara Sales Hewlett-Packard
mmccorm@d.cs.okstate.edu (McCormick Martin) (04/15/91)
I would also like to know how those humidity sensors work. I know that clothes driers have been using humidity sensors for years. If anybody has some information about this, please post to the group. Many thanks. Martin McCormick Oklahoma State University Stillwater, OK Amateur radio WB5AGZ
scottb@hp-vcd.HP.COM (Scott Bigelow) (04/17/91)
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.comafpauls@lims01.lerc.nasa.gov (PAUL SCHWARTZ) (04/18/91)
In article <1991Apr12.113251.16467@minyos.xx.rmit.oz.au>, s882823@minyos.xx.rmit.oz.au (Scott Reynolds [.../* sbr */...]) writes... >I have a question hopefully someone out there in net-land can answer? > >We (a group of 17 Electronic Eng 3rd Year Students) have a 12 week >design project for designing a Micro Controller for a domestic >clothes dryer. After extensive market research (looking in the >local dept. store) found that humidity controlled dryers were >rare - hence our desire to use the exhaust air humidity as a indication >of the dryness. > The problem arises as to selecting an appropriate sensor, considering > the nasty environ. > Does anyone know of sensors used in commerically availiable products > > The dryer which I own will automatically stop when the clothes are dry but it doesn't use a humidity sensor, it uses a temperature sensor. The dryer has a mechanical timer. When the exhaust reaches a certain temperature the heating element turns off and the timer advances. When the temperature get below a certain level the heating element will turn back on and the timer will stop advancing. This process will continue until the timer turns everything off. I can say from using the dryer the system work very well Paul Schwartz
gibbonsj@iccgcc.decnet.ab.com (04/25/91)
stuff deleted >> >>We (a group of 17 Electronic Eng 3rd Year Students) have a 12 week >>design project for designing a Micro Controller for a domestic >>rare - hence our desire to use the exhaust air humidity as a indication >>of the dryness. >> The problem arises as to selecting an appropriate sensor, considering >> the nasty environ. >> Does anyone know of sensors used in commerically availiable products Another problem you will run into is that in gas dryers, the normal by-product of the combustion process (of natural gas) is water vapor, so hudmidity sensors in gas dryers are not very useful. You could look at the relative hudmidity at the beginning of the drying cycle and then compare it to what you normally see at the end of the cycle, but you would run into problems on high-humidity types of days (you might think that the relative hudmidity would not drop enough to consider the load of laundry being dry). Good luck on your project - and beware of the static electricity that is created by overdrying a load of laundry (you know, 'static cling'...). One zap from that will completely destroy a micro system... -- John Gibbons Cleveland, Ohio "Welcome My Son, Welcome To The Machine" - Pink Floyd Of all the things I've lost, I miss my mind the most...