[Weather] termperature offset on Dalsemi station

[Ernie Oporto]

I don't believe the station has a jumper.  I have to unmount it and open it
up this week, so I'll take a look to be sure.

I may have some DS18S20 units on hand back from the days when I would ask
Dalsemi for eval parts every couple of months.  If it's not a SMT part I
should be an easy swap.



On 3/31/07, Tim Bitson <tbitson at mac.com> wrote:
>
> Ernie,
> The original DS1820 temp sensor has a design flaw. The design was
> corrected and the fixed parts became DS18S20. Some of the early weather
> stations had the defective parts in them. At the time, Dallas Semi was
> offering free replacements, but I doubt that's true any more. You can order
> a DS18S20 from Hobby-Boards.com or Digikey and replace the sensor in your
> wind instrument (it is soldered in place).
>
> Just out of curiosity, do you have the shorting jumper installed on your
> wind instrument? Usually the lack of a jumper causes the temp to read zero,
> but it could cause the problem you're experiencing.
>
> Using the DS2438 (the 1-Wire chip in the humidity sensor) is perfectly
> acceptable. It has a slightly higher accuracy (2 degs C verses 1 deg C for
> the DS18S20)., but if your getting good reading, then there is no reason you
> shouldn't use it.
>
> Tim
> http://www.weathertoys.net
>
>
>
> On Mar 31, 2007, at 10:31 AM, Ernie Oporto wrote:
>
>
> I forgot to mention that the internal sensor temp is actually 7-10 degrees
> LOWER than the real temp.
> But I can guess that because the thing is in the shade it keeps the cool
> air inside from the night before and never heats up.  I made a pagoda a few
> years ago for the humidity sensor out of a lawn lamp, so I'll just do the
> same for this.
>
> Does anyone recommend AGAINST using the Trh sensor for temp?  I seem to
> recall that had issues too.
>
>
>
> On 3/30/07, Rich Mulvey < weather at mulveyfamily.com> wrote:
> >
> > Ernie Oporto wrote:
> > >
> > > You can see at the link below that my Dalsemi station seems to send
> > > data that is 7-10 degrees off from other stations around me.  Most of
> > > the time this is because my station is in the shade due to my condo
> > > complex's rules about where I can mount things.  Of course, at night,
> > > we are all in the shade and the temperature difference is still
> > > there.  This is one of the original dalsemi 1-wire stations.
> > >
> > > http://www.findu.com/cgi-bin/wxnear.cgi?call=CW0861
> > >
> > > Surprisingly, the Trh in my humidity sensor (one of the original
> > > humidity sensors that were sent out in samples) seems to show the
> > > right temperature.  I'm sure I can fudge OWW to read the temp from the
> >
> > > humidity sensor for sending to findu.com <http://findu.com>, but I'd
> > > like to see if I can get to the root of the problem and correct the
> > > temp.  Is there any known issue I should be looking for that might
> > > cause this?  Any recommendations?
> > >
> >
> >
> >    Is this the temperature sensor mounted in the DalSemi weather head?
> >
> >    If so - you're *never* going to be able to get a reliable, consistent
> >
> > reading from it.  The problem is that the sensor is mounted in a sealed
> > enclosure, and thus is not measuring the air temperature - it will be
> > offset based on the amount of sunlight, cloudiness, how much heat is
> > being absorbed by the weather head, etc.  So you'll generally see the
> > temps running high in the daytime, and low at night.  You can't just
> > apply an offset to the temps, because there are so many variables that
> > will affect the measurement.
> >
> >    The solution is to mount a completely separate temp sensor in a
> > properly ventilated enclosure - google for "weather pagoda" or
> > "stevenson screen" for many ideas in that regard.
> >
> > - Rich
> >
> >
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> >
>
>
>
> --
> Ernie
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-- 
Ernie
http://www.shokk.com/blog/
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