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'Humidity Sensor'
1997\05\11@091028 by Ricardo Barbosa

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       I'm looking for a humidity sensor.
       Anybody know?
       Thanks
       Ricardo
       spam_OUTrcbarbosaTakeThisOuTspamriopreto.com.br

1997\05\11@205431 by Larry G. Nelson Sr.

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At 10:14 AM 5/11/97 -0300, you wrote:
>        I'm looking for a humidity sensor.
>        Anybody know?
>        Thanks
>        Ricardo
>        .....rcbarbosaKILLspamspam@spam@riopreto.com.br
>
Panametrics and Vaisala make humidity sensors. I have used the Panametrics
sensors in the past with good results. The capacitance of the sensor
changes with relative humidity. They have an application note using a 556
timer to give a PWM output that can be integrated into a DC voltage
proportional to RH.


Larry G. Nelson Sr.
L.NelsonspamKILLspamieee.org
http://www.ultranet.com/~nr

1997\05\11@212055 by Steve Hardy

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> >        I'm looking for a humidity sensor.
> >        Anybody know?
> >        Thanks
> >        Ricardo
> >        .....rcbarbosaKILLspamspam.....riopreto.com.br

Probably not what you're after, but I have had some success with the
following design, which uses wet-bulb/dry-bulb measurements along with
a table of wet-bulb depression implemented by a microproessor.

Two NSC temperature sensors are used (LM335Z I think).  These look like
zeners whose breakdown voltage is proportional (10mV/K) to absolute
temperature.  The output is 2.73V for 273 Kelvins.  A pair of op-amps
is used to measure the absolute temperature indicated by the dry
sensor, and the difference in temperature between dry and wet.  The
signals are converted into current sources which are remotely sensed by
resistors, and the resulting voltage fed into a multiplexed ADC.  The
microprocessor converts the readings into temperature and relative
humidity by looking up a table and interpolating where necessary.

The wet sensor is kept moistened by a wick.  Of course this is probably
too inconvenient for most practical applications, but does have the
advantage of not requiring calibration.  Also, the parts are very easy
to find.

Regards,
SJH
Canberra, Australia

1997\05\13@024819 by Tim Modra

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----------
> From: Ricardo Barbosa <EraseMErcbarbosaspam_OUTspamTakeThisOuTRIOPRETO.COM.BR>
> To: PICLISTspamspam_OUTMITVMA.MIT.EDU
> Subject: Humidity Sensor
> Date: Sunday, 11 May 1997 23:14
>
>         I'm looking for a humidity sensor.
>         Anybody know?
>         Thanks
>         Ricardo
>         @spam@rcbarbosaKILLspamspamriopreto.com.br

I'm about to try the SMARTEK polymer humidity sensor,
claimed to be good right up to 100% RH.  Sourced from Farnell 625-917.

Anybody else tried these ?


Tim Modra

1997\05\15@061152 by Tom Handley

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  Ricardo, I'm working on a 16C74-based weather station and I've looked
at a variety of humidity sensors. Low-cost sensors behave like capacitors
that vary with humidity to change the frequency of an external oscillator.
Typical relative humidity ranges from 10 - 90%. In addition to the other
sensors mentioned, Philips makes a low-cost sensor (P/N 2322 691 90001).

  For my project, I needed better accuracy and I wanted to reduce the
complexity of the support circuitry. I ended using HyCal sensors which
provide an output within 0-5V and require minimal support. The outdoor
sensor is an IH-3602L which comes in a T0-39 can with a slotted cap and
for the indoor sensor, I used the IH-3605 hybrid element. Both sensors
operate from 0 - 100% and provide an output from around 0.8V - 3.9V with
a 5V supply. They require a simple low-pass filter and, as with most
sensors, need to be shielded from sources of bright light. You do need
to factor in temperature compensation so you need to measure ambient
temperature near the sensor.

  For more info, contact:

     Philips, (817) 325-7871
     HyCal,   (818) 444-4000

  - Tom

At 10:14 AM 5/11/97 -0300, you wrote:
>        I'm looking for a humidity sensor.
>        Anybody know?
>        Thanks
>        Ricardo
>        KILLspamrcbarbosaKILLspamspamriopreto.com.br


'humidity sensor'
1998\05\18@091442 by Kolesnikoff, Paul
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Hi,
Awhile ago there was a thread on humidity sensors. One of the
recommended vendors was Panametrics with their RH2 sensor. This is
supposedly a low cost humidity sensor. However, their "sampling" program
is to sell me 3 for $100US. This hardly qualifies as low cost or
sampling. Does anyone have any other sources for a humidity sensor or
better yet a way to build your own?

Thanks,
Paul K.

PS I will be interfacing this to a PIC. So it is not quite OT.

1998\05\18@144518 by Peter L. Peres

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>3 @ $100

 I commiserate.

> build your own

 Yes there is, there are several ones in fact. Problem: not readily
reproductible under production conditions.

 So here goes: Take a tube of inox steel about 20 mm long, 5 mm dia.
Solder a wire to it. Take a piece of dense gauze (medical supply) or a
piece of lint-free cloth, cut into strip suitable to be wound around tube
about 2 windings. Soak it in a saturated kitchen salt solution (dissove as
much salt in 1/2 glass of water as you can add until salt starts piling up
at the bottom), then wind wet around tube. Wind a piece of
corrosion-resistant wire several times around this (de-insulated
wire-wrapping wire works), and secure (do this while wet). Dry the
contraption completely. You may want to select a pair of electrodes that
withstand HCL and HCLO. Platinum and Gold are ideal, alas the price...

 This works best when sensed with AC current, with DC it tends to
polarize after a short time and cause misreadings. To obtain AC with a
PIC, drive an output pin at a few Hz, and use the 1/2 Vcc supply as
reference for the sensor ;).

 The sensor's impedance is very high in dry air and becomes low when wet
air is present. There is another variant that uses graphite electrodes.
That is much more corrosion resistant (lasts almost forever), but is very
delicate to build.

 Sensor response is slow (1/2 hour) for small variations, but very fast
for getting wet (practically instant). It should not be immersed.

 There is another type of commercial sensor for this, that is much
better. There is one of these in each VCR and camcorder. It's piece of
white ceramic with electrodes deposited on it and 2 connections. It shows
high impedance when dry and low (5 kohm or less) when humid. This is a
GO/NO GO sensor. The transition is abrupt and response time of the order
of 5-10 seconds. You can scrap one from a dead VCR for testing.  These
sensors like to get contaminated sometimes, and get stuck in the low Z
region. In this case, they are useless. To determine, measure sensor
removed from VCR in Ohms scale, should show incredibly high (much more
than 100 kohm in dry air). They are very sensitive to dew from human
breath among other things. If tripped, allow to dry for 30 minutes.
Cigarette smoke seems to be a contaminating factor but I'm not certain.
These must NEVER be immersed. They are known as 'dew sensors'.

hope this helps,

Peter


On Mon, 18 May 1998, Kolesnikoff, Paul wrote:

{Quote hidden}

1998\05\18@195527 by Tom Handley

picon face
  Paul, while I can't help with current pricing here is some `canned' info
that I've saved from previous projects:

  Philips makes a low-cost sensor (P/N 2322 691 90001). General Eastern also
seems to have interesting low-cost sensors in their G-CAP line. Their sensors
cover 1 - 100% RH.

  For my project, I needed better accuracy and I wanted to reduce the
complexity of the support circuitry. I ended up using HyCal sensors which
provide an output within 0 - 5V and require minimal support. The outdoor
sensor is an IH-3602L which comes in a T0-39 can with a slotted cap and for
the indoor sensor, I used the IH-3605 hybrid element. Both sensors operate
from 1 - 100% and provide an output from around 0.8V - 3.9V with a 5V
supply. They should be buffered and require a simple low-pass filter and, as
with most sensors, need to be shielded from sources of bright light. You do
need to factor in temperature compensation so you need to measure ambient
temperature near the sensor. You normally combine both in a package for your
outdoor sensors.

  For more info, contact:

     HyCal          : (818) 444-4000
     Philips        : (817) 325-7871
     General Eastern: (800) 225-3208

  - Tom

At 07:12 AM 5/18/98 -0600, you wrote:
{Quote hidden}

1998\05\18@220140 by Gavin Jackson

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part 0 1008 bytes
I've used a sensor made by TDK. The device number is
CHS-GSS. It requires a 5 volt supply and produce a voltage
that ranges from 0 - 1V in 10mV steps that represents
the relative humidity between 0% - 100%.

Great little sensor!

Gavin
--------------------------
RemoveMEvulcanTakeThisOuTspamihug.co.nz
www.geocities.com/TheTropics/Cabana/2625
--------------------------


{Original Message removed}


'Humidity sensor'
1999\06\09@010751 by Peter Tran
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Can anyone tell me where I can find the humidity sensor. Thank you.

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1999\06\09@073914 by Tim Hamel

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> NetZero - We believe in a FREE Internet.  Shouldn't you?
>  Get your FREE Internet Access and Email at
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NetZero is so easy to hack.  If you don't want (or like) the constant on-top
window, talk to me. I can fix it up like a REAL ISP, no ads, no software, no
problem.

1999\06\09@102539 by Tom Handley

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  Peter, contact the following vendors:

     HyCal: www.honeywell.com/sensing/prodinfo/humiditymoisture
     Philips        : (817) 325-7871
     General Eastern: (800) 225-3208

  - Tom

At 09:51 PM 6/8/99 -0700, Peter Tran wrote:
>Can anyone tell me where I can find the humidity sensor. Thank you.
>
>________________________________________________________
>NetZero - We believe in a FREE Internet.  Shouldn't you?
>Get your FREE Internet Access and Email at
>http://www.netzero.net/download/index.html

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