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RE: Dry Cameras
Rube Goldberg would be proud. But you forgot the mouse and the alarm
clock. The alarm clock goes off, the mouse jumps up to eat the cheese, the
string attached to the cheese turns on the laser...
OK, I am just looking for a simple device. I already have a precision data
system built into my telescope, so all I need is a sensor.
I even have a catalog picture of one.
In Newark Catalog 114 it is listed on page 288 at $8.53
In Newark Catalog 116 it is listed on page 721 at $13.83
Hmmmm! If the trend continues I cannot afford it. The device is
apparently the Philips Type 232269190001
I have not been able to get through to the Newark home page. Does anyone
know if they are still in business? The signs have not been good lately,
and I have not placed an order with them for a while.
I have been to the Philips home page and cannot find it. This is typical
for a big company like Philips, they make so much that your chance of
finding it is small. They keep sending me to the laser optics page, where
there is no clue about a relative humidity sensor.
Now jamie points out that you can buy a complete weather station at Radio
Shack for a few bucks. I also pointed out that such instruments are
available from Cole-Parmer. Now all I want is the blinkin sensor. They
must be made somewhere, but I can't find them.
Tom Droege
At 05:55 PM 5/11/00 -0400, you wrote:
>I can't stand it any more.
>
>The gadget that Tom remembers is a sling psychrometer, it works sort of like
>a wet-bulb thermometer, except that the forced air flow from waving it in
>the air gives a quicker result.
>
>A wet-bulb thermometer gives you an indication of how fast the water is
>evaporating from the wick; the faster the evaporation, the drier the air,
>and the greater the temperature difference between the wet-bulb and dry-bulb
>thermometers the lower the relative humidity. The actual dew point and
>relative humidity have to be determined from tables. The wet-bulb
>temperature is *not* the dew point. You don't need to move air over a
>wet-bulb/dry-bulb thermometer setup; diffusion will do the job if it is not
>sealed up.
>
>But Tom? Given everything else that's going on in your setup, and given all
>the Peltier coolers you have flying around, you are in a position to measure
>the dew-point simply and directly, assuming you are too far from an airport
>to trust the aviation weather reports.
>
>Attach a polished piece of metal to the cold side of a Peltier cooler.
>Attach a thermometer to it. Bounce a light source off the metal into a
>sensor. Ramp the TEC current up until frost begins to form on the polished
>metal, interfering with the reflected light. Read the dew point off of the
>thermometer.
>
>
>> -----Original Message-----
>> From: owner-tass@listserv.wwa.com [mailto:owner-tass@listserv.wwa.com]On
>> Behalf Of Chris Albertson
>> Sent: Thursday, May 11, 2000 17:17
>> To: Tom Droege; tass@listserv.wwa.com
>> Subject: Re: Dry Cameras
>>
>>
>>
>> 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
>>
>
>
>