Re: Dry Cameras

[Chris Albertson <calbertson@logicon.com>]

I figured a wet bulb thermometer would be pretty reliable.  I think
you only need to blow air over it if you are in a hurry to get a reading.
One set up permanently could have a cadge built over it. As for a source
of water, a soda one liter bottle would last forever almost.

If you have some money to spend why not get a full on weather station
complete with an RS-232 interface to a computer.  For about $400 you
can get a pretty complete system.  These are easy to find.  I know of
at least one place that sells them.

Then there is the zero cost software-only dew point sensor.
You get the aviation weather reports off the web and extract
the dew point from the message.

Tom Droege wrote:
> 
> Chris and all,
> 
> Yes, I think Chris is right about the dew point.  There are extra
> thermometer positions available in the system so one could be dedicated to
> a wet bulb thermometer.  I am using the AD-590 which is a similar device.
> But I don't much like a themometer with a wet sock hanging on it.  For one
> thing, you will have to blow air on it to get a reasonable reading.  I used
> to make this measurement at a power plant.  You have this wet bulb
> thermmeter on a chain and you sling it around to circulate the air around
> it.  I would better like a relative humidity sensor direct, even if the
> reading were not so good.  I am opting for as much reliability as I can
> get.  The bears are apt to come by and drink the water, or some such thing.
> 
> Tom Droege
> 
> At 12:59 PM 5/11/00 -0700, you wrote:
> >
> >I asked this question on the list a week or so ago. I wanted
> >to know how to measure the dew point.  I figured I'd control the cooling
> >water temp to a little over the dew point too.
> >
> >The answer I got was simply that the dew point equals the wet-bulb
> >thermometer reading.  (Easy to verify this with a glass thermometer.)
> >Just put your standard air temp sensor in a wick over a container of
> >water.  I think there is a part LMxxx that reads out temp directly.
> >
> >> Does anyone know a source for a cheap, not too accurate relative humidity
> >> indicator?  I would like one powered by 5 or 15 volts, and which puts out
> >> only a modest signal.  The ADC measurement system has a least significant
> >> bit of 300 micro volts.  Something with say 3mv or more per % relative
> >> humidity would be fine.  I think I can tolerate almost any scale factor
> >> that such a device would have.
> >>
> >> I would like to sense the relative humidity.  I already sense the
> >> temperature.  With the two, I think one can compute the dew point.  I would
> >> then regulate the cooling water just above the dew point.
> >>
> >> Tom Droege
> >
> >--
> >  Chris Albertson
> >
> >  calbertson@logicon.com                  Voice: 626-351-0089  x17
> >  Logicon, Pasadena California            Fax:   626-351-0699
> >
> >

-- 
  Chris Albertson

  calbertson@logicon.com                  Voice: 626-351-0089  x17
  Logicon, Pasadena California            Fax:   626-351-0699