Probably depends on what kind you want. I have a few, electronic with
probe out a window, those on deck and porch that you have to look
through a window to read and one remote from Cabela's that give
temperature and humidity. All appear to be accurate but depending on
side of house can vary as much as 10 degrees if in sun or not.
I bought one of those round outdoor thermometers, and in the store, they
had about 50 of them. I noticed about a 10deg difference when I looked
at many of them on the shelf. I opted to buy one that was closest to the
majority of them. I know they are not 100% accurate. They just operate
on a bi-metal coil, and none of them are "true", and even the sticker
that shows the numbers on them might be applied a little differently.
But they are close enough for a rough idea of the temp. For real
accuracy, a digital one (and expensive one) would probably be closer to
accurate, than a bi-metal coil or mercury type thermometer.
Look at some of the remote units that can be close to properly mounted.
By properly, there are guidelines for "official" temperature readings
official measurements are taken about 1.5 meters above the ground, in a
white shelter that is ventilated at a certain rate. The white color
(ideally) gives the shelter a very high albedo, close to 100%, which
means that it won't absorb sunlight and warm up... the ventilation keeps
the air mixed and fresh (think greenhouse effect, or lack thereof).
The Davis system here seems to match "official" temp's to within 1F
routinely and is, of course, a weather station not just a thermometer.
It does, of course, require having somewhere to mount it to be useful;
it won't just stick on the outside of the house where can see the face
to read it thru a window; OP didn't really give much in the way or
limitations to go on.
OTOH, most ordinary mercury run-o-the-mill thermometers are precise to
within a couple degrees or even better; the key to accuracy is
"location, location, location". The old round-face analog here is on
the underside of the eave support on the north porch where it's well
shaded, has air circulation and is far-enough from the outer wall of the
house (7-8 ft) it doesn't seem affected by heat loss in the winter much
and it virtually always is within the precision of the scale of the Davis.
I've always been amazed at how close the automobile temperature sensors
track NWS reports once they have enough air-flow around their
sensors--rarely does the car not read also within a degree or two of the
NWS report altho I do note that during the winter it will tend to
measure a couple degrees warmer when get to the blacktop off our gravel
road as it is picking up the warmer layer there from the sun on the
black surface. Just a side note, unrelated to the question itself...
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No kidding - both our cars seem to be quite accurate.
I wonder if it would be easy to pilfer the components from
scrap cars and re-purpose them ?
I wouldn't know where to begin, though.
It would likely involve the car's computer + its wiring -
- which would count-me-out !
On 08/10/2016 3:52 PM, firstname.lastname@example.org wrote:
Probably very little, actually; they're just a NTC thermistor -- all
you'd need would be a 5VDC power supply and way to read the resulting
output resistance and know the calibration curve...I think most(?) in
recent model years are pre-linearized from the vendors but that's
hypothesis, not confirmed.
Just to get a signal proportional to temperature would be essentially
trivial, it'd take a little more effort to actually show that as ambient
but not a lot...
I'm more impressed that they can get the airflow right and avoid the
contamination of the measurement from engine heat and all than the base
sensor; altho come to think of it I don't know where the doggone thing
is mounted on any of my vehicles...they'll be at 120F or somesuch after
the car's been idle in the sun for a while until get enough speed up and
some time to cool the actual sensor itself but give it 2-3 minutes and
over a city crawl and they'll be right on again...
On one of my cars the sensor was right behid the grill Very accurate
unless I went through a car was and then it took two days to work again.
Rain never bothered it.
One hot August day I thought everything went crazy. I was on the NJ
Turnpike and pulled into a rest area. It was 1:01 in the afternoon,
temperature was 101 and the radio was tuned to 101.1
I've had one of these for years... it's plenty accurate
There is also http://mesonet.org/ here... and an ornamental windmill in
the back yard to know which way the wind is blowing and how much. It's
89.5 F on the front porch right now so says the remote sensor and it's
9:38 PM ... so says the Navy's Atomic clock. The Taylor round plastic
thermometers you can adjust. Taylor now there's a name you can trust
when it comes to thermometers.
On Wednesday, August 10, 2016 at 2:26:57 PM UTC-4, Ed Pawlowski wrote:
When I was stationed in Alaska while serving in the USCG, we were the
official NOAA weather station for our region. Heck, we were the only
*people* in our region. ;-)
We had one of those white shelters with slatted doors, etc. We had to
go outside every few hours(?) and take wet bulb readings, dry bulb
readings, etc. We had a hand-held spinner do-hicky that held the
thermometers. IIRC, we'd dip the end of the thermometer, which was
covered with a cotton "sock", in alcohol, spin it for some
specified period of time and then record the reading.
The shelter may have started at 1.5 meters above the ground, but by
mid-winter when the stairs had been carved into the snow so we could
get out of the building, we'd be reaching down into the shelter to
get the equipment.
This isn't the one in AK, but it's the same kind:
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