any way to calibrate digital thermometer?

[Johnny Appleseed]

I have a digital thermometer like the one here:

http://www.walmart.com/ip/Acurite-Wireless-Thermometer/16888921

The temperature the outdoor sensor reads is at least 3 degrees off from what
it should be. Is there any way to adjust the temperature reading in these
units? The instructions don't say anything about this issue.

Thanks,
John

[William Sommerwerck]

Make a calibration chart.

[nesesu]

John, if you can open the outdoor unit, look and see if there is any tiny potentiometer inside. It is likey that the calibration resides with the analog sensor before the signal is digitized for transmission. If there is a pot [not a trimmer cap for the RF] then note it's position and then adjust it and see if the temperature reading changes. If not, set it back to original and live with it.

Neil S.

[Jeff Liebermann]

On Tue, 29 May 2012 11:36:59 -0400, "Johnny Appleseed"
<no...@nowhere.non> wrote:

>I have a digital thermometer like the one here:
>
>http://www.walmart.com/ip/Acurite-Wireless-Thermometer/16888921
>
>The temperature the outdoor sensor reads is at least 3 degrees off from what
>it should be.

Move the thermometer into the shade, away from sources of heat
(vents), and away from anything that will reflect or accumulate heat
(black meal objects). You want to measure the air temperature, not
the temperature of the reflected sun.

Also, how do you know what it "should be"? Your "reference"
thermometer might be just as far off. Incidentally, 3 degrees
variation isn't all that bad.

Such accuracy issues are constant source of entertainment among those
that weather stations that appear on the internet. Some really good
hints:
<http://www.wxqa.com/aprswxnetqc.html>
Here's one that I help maintain:
<http://weather.gladstonefamily.net/site/AR779>
Oops. I forgot to calibrate the barometer to altitude the last time
the power died and the backup battery lasted about 2 hours. Anyway,
this is my version of what it takes to get decent temperature
readings:
<http://802.11junk.com/jeffl/pics/wx/slides/radiation-shield-01.html>
It's called a "radiation shield" or "pagoda". The idea is to keep the
sensor out of direct (or indirect) sunlight, while still allowing for
air flow. However, there's still a problem. The building is a remote
radio site with lots of warm transmitters inside. The slit near the
roof allows hot air from inside the building to dribble out of the
slit. It was close enough to affect the sensor to have had an effect.

None of the cheapo wireless weather sensors have a proper radiation
shield including yours.

>Is there any way to adjust the temperature reading in these
>units? The instructions don't say anything about this issue.

Not on the cheap wireless sensors. The basic thermistor accuracy is
about +/-0.2% of full scale, which is less than 1 degree. Calibration
isn't really an issue. What is an issue is whether you're measuring
air temp, ground temp, wall temp, reflected sky temp, vent temp, etc.

--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[mike]

There's an old saying...
A man with one watch always knows what time it is. A man
with two watches, not so much.
Same goes for thermometers.

Publish what you find out. I've got the same problem.

For me, the only temp that really matters is the temp at which
the pipes freeze.

[John Robertson]

Jeff Liebermann wrote:
> On Tue, 29 May 2012 11:36:59 -0400, "Johnny Appleseed"
> <no...@nowhere.non> wrote:
>
>> I have a digital thermometer like the one here:
>>
>> http://www.walmart.com/ip/Acurite-Wireless-Thermometer/16888921
>>
>> The temperature the outdoor sensor reads is at least 3 degrees off from what
>> it should be.
>

...

> <http://802.11junk.com/jeffl/pics/wx/slides/radiation-shield-01.html>
> It's called a "radiation shield" or "pagoda". The idea is to keep the
> sensor out of direct (or indirect) sunlight, while still allowing for
> air flow. However, there's still a problem. The building is a remote
> radio site with lots of warm transmitters inside. The slit near the
> roof allows hot air from inside the building to dribble out of the
> slit. It was close enough to affect the sensor to have had an effect.

And if you don't keep it clean, dust/dirt can affect the results...not
to mention wasps possibly finding the inside attractive for a nest (grin).

>
> None of the cheapo wireless weather sensors have a proper radiation
> shield including yours.
>
>> Is there any way to adjust the temperature reading in these
>> units? The instructions don't say anything about this issue.
>
> Not on the cheap wireless sensors. The basic thermistor accuracy is
> about +/-0.2% of full scale, which is less than 1 degree. Calibration
> isn't really an issue. What is an issue is whether you're measuring
> air temp, ground temp, wall temp, reflected sky temp, vent temp, etc.
>

Yup, it is difficult to have precision readings that are consistent over
time. Calibration, calibration, calibration...

John :-#)#

--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

[Charles]

http://www.harborfreight.com/non-contact-pocket-thermometer-93983.html

Just posted as an aside. I am amazed at how well the cheap ones work.

[Jeff Liebermann]

On Tue, 29 May 2012 15:45:59 -0700, John Robertson <sp...@flippers.com>
wrote:

>And if you don't keep it clean, dust/dirt can affect the results...not
>to mention wasps possibly finding the inside attractive for a nest (grin).

On the other side of the building, the property owner has 5 bee hives.
I've become somewhat accustomed to having honey bees buzzing around my
head when working on the radios in the building. Dirt and dust are
not much of a problem. Corrosion damage to the cheap RJ14 connectors
and flat ribbon wire is more of a problem. Whatever inspired the wx
station manufacturers to use telephone connectors is beyond my limited
imagination. Extra credit to Peet Bros for using an RJ50 connector.
That's a 10 pin version of the common 8 pin RJ45 connector.

>Yup, it is difficult to have precision readings that are consistent over
>time. Calibration, calibration, calibration...

The theory is that if you design it randomly, build it randomly,
install it randomly, and poll data randomly, all the errors will
cancel each other out resulting in an accurate reading. Never mind
calibration. Just randomize everything.

I'll confess to having done the ice and boiling water calibration
ceremony to various thermometers while in college, but not to a
wireless sensor.
<http://www.in.gov/isdh/files/ThermometerCalibration__3_.pdf>



--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com je...@cruzio.com
# http://www.LearnByDestroying.com AE6KS

[Jeff Liebermann]

My father one told me to beware of anything that is amazing, magical,
miraculous, etc. They rarely are.

I have one of those Centec pocket thermometers. It's great for
cooking. However, there's a problem or three. The beam width is
about 90 degrees making it very difficult to measure the temperature
of an object, without also including the temperature of the
surroundings. An upper limit of 110C means that won't work under the
hood of my car, or for measuring the temperature of my wood burner,
barbeque, or hibachi. There are better units for not much more and
that have a narrower beam width (none of which can seem to get the
laser to align with the measurement spot).

Using an IR thermometer for measuring air temperature is somewhat of a
problem. The air has a very low mass and therefore emits very little
IR light for the device to measure. A solid object that's in thermal
equalibrium with the air temperature will work, but only if it has the
preset 0.95 emissivity. Going outside and measuring the temperature
of various building walls, plants, planters, and dirt, I get wide
variations in readings. The wood planter seems to be the closest to
the air temperature.

[Phil Allison]

"Johnny Appleseed"

>
>I have a digital thermometer like the one here:
>
> http://www.walmart.com/ip/Acurite-Wireless-Thermometer/16888921
>
> The temperature the outdoor sensor reads is at least 3 degrees off from
> what it should be.

** How do the two readings compare if the whole caboodle is indoors ?

Much depends of the siting of the outdoor sensor - it needs to be in a shady
spot and get a bit of breeze.

> Is there any way to adjust the temperature reading in these units?

** Have look inside yours.

The non radio linked kind generally have no adjustments.


... Phil

[gregz]

Jeff Liebermann <je...@cruzio.com> wrote:
> On Tue, 29 May 2012 19:11:25 -0400, "Charles"
> <charles...@comcast.net> wrote:
>
>> http://www.harborfreight.com/non-contact-pocket-thermometer-93983.html
>> Just posted as an aside. I am amazed at how well the cheap ones work.
>
> My father one told me to beware of anything that is amazing, magical,
> miraculous, etc. They rarely are.
>
> I have one of those Centec pocket thermometers. It's great for
> cooking. However, there's a problem or three. The beam width is
> about 90 degrees making it very difficult to measure the temperature
> of an object, without also including the temperature of the
> surroundings. An upper limit of 110C means that won't work under the
> hood of my car, or for measuring the temperature of my wood burner,
> barbeque, or hibachi. There are better units for not much more and
> that have a narrower beam width (none of which can seem to get the
> laser to align with the measurement spot).
>
> Using an IR thermometer for measuring air temperature is somewhat of a
> problem. The air has a very low mass and therefore emits very little
> IR light for the device to measure. A solid object that's in thermal
> equalibrium with the air temperature will work, but only if it has the
> preset 0.95 emissivity. Going outside and measuring the temperature
> of various building walls, plants, planters, and dirt, I get wide
> variations in readings. The wood planter seems to be the closest to
> the air temperature.
>

You can hold up a piece of paper in front and measure air temp. You can
even tape a piece of paper on the front. Just stay out of sunlight.

Greg

[gregz]

Outdoor remote sensors. Something I asked for a couple years before they
existed for home use.

Mine vary. I have two. 2-3 degrees. I have not tinkered with circuitry. I
also have a third I have not compared. One is under my porch roof. As the
patio heats up from the sun in the afternoon, it rises from true ambient.

It's very tricky to calibrate ordinary probe devices, something I did
frequently. Probes need to be on top of each other. Even in water, you must
circulate it very fast for accuracy.

Greg

[isw]

In article <jq2qes$hn$1...@dont-email.me>,

If it's reading high, you might be able to hack a resistive divider to
improve things. If it's reading too low, there's probably not much you
can do.

Isaac

[John Robertson]

Jeff Liebermann wrote:
> On Tue, 29 May 2012 15:45:59 -0700, John Robertson <sp...@flippers.com>
> wrote:
>
>> And if you don't keep it clean, dust/dirt can affect the results...not
>> to mention wasps possibly finding the inside attractive for a nest (grin).
>
> On the other side of the building, the property owner has 5 bee hives.
> I've become somewhat accustomed to having honey bees buzzing around my
> head when working on the radios in the building. Dirt and dust are
> not much of a problem. Corrosion damage to the cheap RJ14 connectors
> and flat ribbon wire is more of a problem. Whatever inspired the wx
> station manufacturers to use telephone connectors is beyond my limited
> imagination. Extra credit to Peet Bros for using an RJ50 connector.
> That's a 10 pin version of the common 8 pin RJ45 connector.
>
>> Yup, it is difficult to have precision readings that are consistent over
>> time. Calibration, calibration, calibration...
>
> The theory is that if you design it randomly, build it randomly,
> install it randomly, and poll data randomly, all the errors will
> cancel each other out resulting in an accurate reading. Never mind
> calibration. Just randomize everything.

So is that how some researchers get accuracy to .001 using
hundreds/thousands of devices calibrated to 0.1?

>
> I'll confess to having done the ice and boiling water calibration
> ceremony to various thermometers while in college, but not to a
> wireless sensor.
> <http://www.in.gov/isdh/files/ThermometerCalibration__3_.pdf>

Put the sensor in a baggie and suck the air out then see how it measures
up...

[William Sommerwerck]

I remain amazed. I gave a simple answer, which was implicitly endorsed by
another person, but which has been ignored.

"The Lady from Philadelphia" recommends the following...

Place the conventional thermometer you trust and the transmitter in the same
shaded spot. Make a chart with the transmitter's readings in the left
column, the thermometer's readings in the right column. Check the digital
thermometer's reading whenever you care to. When there's a change, walk out
of the house and read the conventional thermometer. (Such an exhausting
trek! Bring plenty of food and water, along with sunscreen and plenty of
books to read. Hire a sherpa to carry it all.) Add both values to the chart.

Is there something wrong with a simple solution? Tell me, I want to know.
Really.

We are talking about a (presumably) cheap digital/remote thermometer, which
likely has //no// calibration controls. (If it has any, it's probably just
one, for a temperature around 75F.) What is it with this hacker mentality
that demands wasting time on something that is just not that important?

[Gareth Magennis]

"William Sommerwerck" <grizzle...@comcast.net> wrote in message
news:jq503v$4om$1...@dont-email.me...

Hacking the thermometer so it gives the correct reading is going to take a
few minutes once the solution is found here, if there is one.

Your method is likely to take a full year.

You are a bit of a knob sometimes, William, no wonder people ignore you.



Gareth.

[William Sommerwerck]

"Gareth Magennis" <sound....@btconnect.com> wrote in message
news:I8udnVbWXfbwklvS...@bt.com...

> "William Sommerwerck" <grizzle...@comcast.net> wrote in message
> news:jq503v$4om$1...@dont-email.me...

> Hacking the thermometer so it gives the correct reading is
> going to take a few minutes once the solution is found here,
> if there is one.

Which is exactly the point. How much time has been wasted on looking for
that solution -- with no results?

I have a wireless thermometer that's part of an atomic clock. Without even
opening it, I'd be willing to bet that the temperature sensing elements
comprise one resistor in series with one thermistor. You were, perhaps,
expecting multiple resistors and thermistors, with two or three pots to get
everything "just right"?

This "knob" is all-too-aware from many years of experience that virtually
all products are built to meet a price point, and that attempts to improve
or customize them //almost// always result in failure.

To give an example... I once owned the Pioneer RT-2000 system. It had
modular electronics and interchangeable half-track two-channel &
quarter-track four-channel head blocks. It was a clever and useful idea,
poorly executed.

When I started making live recordings, it occurred to me to position my dbx
II noise-reduction units between the Pioneer's external electronics
(containing the mic preamps and mixers) and the transport. To my surprise,
there was no improvement in the S/N ratio.

The 0dB sensitivity of the transport electronics was an unbelievably low
0.1V, way below what is commonly taken as line level. When I measured the
S/N ratio of the external electronics at 0.1V output, it was a miserable
50dB. No wonder noise reduction had no effect.

I was obliged to purchase external mic preamps. Re-engineering Pioneer's
crappy electronics might have been a worthwhile project if I were trying to
improve my skills in circuit design. But I wasn't, so what would be the
point? Life is too short.

> Your method is likely to take a full year.
> You are a bit of a knob sometimes, William,
> no wonder people ignore you.

I BEG YOUR FORGIVENESS for trying to see through to the heart of an issue,
of trying to find simple solutions to "complicated" problems -- or of
recognizing that there really is NO PROBLEM at all.

You would do well to pay attention to this "knob". You might learn something
about problem solving. But, of course, you already know everything, right?

[Gareth Magennis]

>
> You would do well to pay attention to this "knob". You might learn
> something
> about problem solving. But, of course, you already know everything, right?
>
>

No, I do not know everything.

I do know that you are a bit of a knob, though.



Gareth.

[William Sommerwerck]

So I take it that, over the years, you have learned nothing new about
problem solving from me? That's a shame.

[Jeff Liebermann]

On Tue, 29 May 2012 22:00:36 -0700, John Robertson <sp...@flippers.com>
wrote:

>So is that how some researchers get accuracy to .001 using
>hundreds/thousands of devices calibrated to 0.1?

They probably bribed the peer reviewers or made some manner of quid
pro quo deal. The lab assistant that ran the numbers probably didn't
care about signifigant figures or the difference between resolution
and accuracy. If it fits in the speadsheet box, it must be correct.

Incidentally, at 0.001C resolution, the heat emitted by the observer
becomes signifigant.

>> I'll confess to having done the ice and boiling water calibration
>> ceremony to various thermometers while in college, but not to a
>> wireless sensor.
>> <http://www.in.gov/isdh/files/ThermometerCalibration__3_.pdf>
>
>Put the sensor in a baggie and suck the air out then see how it measures
>up...

If you let everything equalize to ambient temperature, you'll
eventually get an accurate reading. Incidentally, many black plastic
shipping bags are somewhat transparent to IR.

[John Robertson]

Jeff Liebermann wrote:
> On Tue, 29 May 2012 22:00:36 -0700, John Robertson <sp...@flippers.com>
> wrote:
>
>> So is that how some researchers get accuracy to .001 using
>> hundreds/thousands of devices calibrated to 0.1?
>
> They probably bribed the peer reviewers or made some manner of quid
> pro quo deal. The lab assistant that ran the numbers probably didn't
> care about signifigant figures or the difference between resolution
> and accuracy. If it fits in the speadsheet box, it must be correct.
>
> Incidentally, at 0.001C resolution, the heat emitted by the observer
> becomes signifigant.
>
>>> I'll confess to having done the ice and boiling water calibration
>>> ceremony to various thermometers while in college, but not to a
>>> wireless sensor.
>>> <http://www.in.gov/isdh/files/ThermometerCalibration__3_.pdf>
>> Put the sensor in a baggie and suck the air out then see how it measures
>> up...
>
> If you let everything equalize to ambient temperature, you'll
> eventually get an accurate reading. Incidentally, many black plastic
> shipping bags are somewhat transparent to IR.
>

I meant to seal the device in a bag and then put in boiling (@ sea
level) or ice water for calibration. Sorry that I wasn't clear enough,
my bad!

[hr(bob) hofmann@att.net]

On May 30, 1:06 pm, John Robertson <s...@flippers.com> wrote:
> Jeff Liebermann wrote:

> > On Tue, 29 May 2012 22:00:36 -0700, John Robertson <s...@flippers.com>

>        "Old pinballers never die, they just flip out."- Hide quoted text -
>
> - Show quoted text -

Boiling water will soften the plastic bag (if it's anything like the
plastic bags we get around here for groceries) to the point that a
leak is almost sure to happen.

[mike]

This is a bad idea on many levels.
Check the operating temperature range. it's unlikely that it included
100C.
Even if it survives...
Most electronic temperature measurement methods rely on some form
of linearization. Calibrating at twice the intended operating temperature
range is unlikely to improve the readings at normal temps.

Do the math on boiling temperature. You've just converted your
inability to measure temperature into an inability to measure
atmospheric pressure.

[John Robertson]

Well, there are bags that are proof to 100C, folks boil their lunch in
them...

However the point was raised about the survivability of the unit to
100C. I was actually only thinking of exposing the sensor to the hot
water, not the module. Again, I need to be clearer in my descriptions.

Sigh.

[Jeff Liebermann]

On Wed, 30 May 2012 11:06:43 -0700, John Robertson <sp...@flippers.com>
wrote:

>I meant to seal the device in a bag and then put in boiling (@ sea
>level) or ice water for calibration. Sorry that I wasn't clear enough,
>my bad!

Boiling Water in a Plastic Bag
<http://www.youtube.com/watch?v=9zFo3vQAIeM>

Boiling water in a paper cup
<http://www.youtube.com/watch?v=xGseQk_r9EI>
<http://www.youtube.com/watch?v=lFL2B_14sLc>

As long as the water keeps the plastic bag and paper cup temperature
below the plastic melt or paper ignition points, there's no problem.

Quiz: What's the difference in water temperature between a slow boil
and a fast rolling boil?
Answer: None.
Moral: It doesn't pay to bring the tea kettle to a violent rolling
boil because the tea will not get any hotter than 100C (at STP).

[Jeff Liebermann]

On Wed, 30 May 2012 13:02:53 -0700, mike <spa...@gmail.com> wrote:

>Do the math on boiling temperature. You've just converted your
>inability to measure temperature into an inability to measure
>atmospheric pressure.

Boiling Points of Water at Various Elevations
<http://www.engineeringtoolbox.com/boiling-points-water-altitude-d_1344.html>

Roughly a 1C drop in the boiling point for a 1000ft gain in altitude.
No need to measure atmospheric pressure. You can read your altitude
from a topo map, compensate for the boiling point, and still be quite
accurate at calibrating the thermometer. The effects of atmospheric
pressure are negligible:
<http://wiki.answers.com/Q/How_does_the_elevation_and_air_pressure_affect_the_boiling_point_of_water>
Unless there's a hurricane coming, the typical changes in atmospheric
pressure might change the boiling point over a +/-1C range.

[isw]

In article <9vqds79jt9a8ngrd5...@4ax.com>,

Jeff Liebermann <je...@cruzio.com> wrote:

> On Wed, 30 May 2012 11:06:43 -0700, John Robertson <sp...@flippers.com>
> wrote:
>
> >I meant to seal the device in a bag and then put in boiling (@ sea
> >level) or ice water for calibration. Sorry that I wasn't clear enough,
> >my bad!
>
> Boiling Water in a Plastic Bag
> <http://www.youtube.com/watch?v=9zFo3vQAIeM>
>
> Boiling water in a paper cup
> <http://www.youtube.com/watch?v=xGseQk_r9EI>
> <http://www.youtube.com/watch?v=lFL2B_14sLc>
>
> As long as the water keeps the plastic bag and paper cup temperature
> below the plastic melt or paper ignition points, there's no problem.
>
> Quiz: What's the difference in water temperature between a slow boil
> and a fast rolling boil?
> Answer: None.
> Moral: It doesn't pay to bring the tea kettle to a violent rolling
> boil because the tea will not get any hotter than 100C (at STP).

But it can (depending on the local barometric pressure) be enough lower
to mess up an otherwise good calibration run ...

Isaac

[isw]

In article <jq5ue2$cih$1...@dont-email.me>, mike <spa...@gmail.com>
wrote:

The friendly folks at the local airport will do that for you, and put
the results on the internet ...

Isaac

[Jeff Liebermann]

On Wed, 30 May 2012 21:40:45 -0700, isw <i...@witzend.com> wrote:

>But it can (depending on the local barometric pressure) be enough lower
>to mess up an otherwise good calibration run ...

Having done the boiling water thermometer calibration exercise, I can
assure you that there are a wide variety of other screwups available.

For example, the temperature of the steam above the boiling water is
at a higher temperature than 100C. With a stick type thermometer,
that puts the bimetallic spring out of the water and into the steam.
The result is a botched calibration. However, if you're a typical
freshman fizzix student, that error can be eliminated by totally
immersing the stick thermometer, at the expense of the thermometer,
which doesn't work very well full of water.

Another is slow versus fast boil. While there's no difference in
water temperature between a slow and fast boil, the fast boil does
contain a much larger number of water vapor (gas) bubbles than the
slow boil. This water vapor is at a higher temperature than the
surrounding liquid phase water. If the stick thermometer was
sufficiently covered or enclosed by these bubbles, the temperature
will read higher than 100C.

While atmospheric pressure does have an effect, pollutants in the
water also have an effect. Want to raise the boiling point? Just add
salt.

The type of container and method of heating also has a slight effect.

[mike]

On 5/30/2012 9:18 PM, Jeff Liebermann wrote:
> On Wed, 30 May 2012 13:02:53 -0700, mike<spa...@gmail.com> wrote:
>
>> Do the math on boiling temperature. You've just converted your
>> inability to measure temperature into an inability to measure
>> atmospheric pressure.
>
> Boiling Points of Water at Various Elevations
> <http://www.engineeringtoolbox.com/boiling-points-water-altitude-d_1344.html>
>
> Roughly a 1C drop in the boiling point for a 1000ft gain in altitude.
> No need to measure atmospheric pressure. You can read your altitude
> from a topo map, compensate for the boiling point, and still be quite
> accurate at calibrating the thermometer. The effects of atmospheric
> pressure are negligible:
> <http://wiki.answers.com/Q/How_does_the_elevation_and_air_pressure_affect_the_boiling_point_of_water>
> Unless there's a hurricane coming, the typical changes in atmospheric
> pressure might change the boiling point over a +/-1C range.
>
>

Well, We don't know where the OP is. I assumed he was concerned about
being off
by 3F. You admit to 3.6F variance due to pressure.
I suggest that it's definitely a factor in increasing the absolute
accuracy of his temp gauge...even if he's in C territory. If I hadn't
mentioned it, I don't think anybody
would have considered that as an error term. And you still don't.

[Spehro Pefhany]

On Tue, 29 May 2012 11:36:59 -0400, the renowned "Johnny Appleseed"

<no...@nowhere.non> wrote:

>I have a digital thermometer like the one here:
>
>http://www.walmart.com/ip/Acurite-Wireless-Thermometer/16888921
>
>The temperature the outdoor sensor reads is at least 3 degrees off from what
>it should be. Is there any way to adjust the temperature reading in these
>units? The instructions don't say anything about this issue.
>

>Thanks,
>John

These type of things use a "precision" thermistor that is supposed to
be good to a degree or so against an internal fixed reference
resistor. There is no individual calibration. You could try to trim
the reference resistor, but personally I'd f'dget about it. 3 degrees
(F?) could be the difference between being in the sun and not, for
example.

What do you expect for < $10?


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

[gregz]

Spehro Pefhany <spef...@interlogDOTyou.knowwhat> wrote:
> On Tue, 29 May 2012 11:36:59 -0400, the renowned "Johnny Appleseed"
> <no...@nowhere.non> wrote:
>
>> I have a digital thermometer like the one here:
>>
>> http://www.walmart.com/ip/Acurite-Wireless-Thermometer/16888921
>>
>> The temperature the outdoor sensor reads is at least 3 degrees off from what
>> it should be. Is there any way to adjust the temperature reading in these
>> units? The instructions don't say anything about this issue.
>>
>> Thanks,
>> John
>
> These type of things use a "precision" thermistor that is supposed to
> be good to a degree or so against an internal fixed reference
> resistor. There is no individual calibration. You could try to trim
> the reference resistor, but personally I'd f'dget about it. 3 degrees
> (F?) could be the difference between being in the sun and not, for
> example.
>
> What do you expect for < $10?
>
>
> Best regards,
> Spehro Pefhany

I got two different devices with fairly constant 3 degree difference. My
one with wind gauge, I don't believe. I think it reads half. I'm going to
take it for a ride some day.
One transmitter failed after a few years. Bought replacement. I have other
cheap units go bad, but my current models are half decent.

Greg

[Jim Yanik]

gregz <ze...@comcast.net> wrote in
news:1440918946360210418.0...@news.eternal-september.o
rg:

My WalMart $10 Acurite wireless remote thermometer also seems to read about
that high.
it's on my covered,screened patio,out of direct sun,and sheltered.

FYI,real cal labs use a platinum platinum-rhodium resistance thermometer
with a correction chart(from NIST) for really precise temp calibrations.
We had a temp-controlled circulating mineral oil bath in which to put the
DUT and reference thermometer.
I used to do that in the USAF.(PMEL)

--
Jim Yanik
jyanik
at
localnet
dot com

[gregz]

Oh, I remember PMEL. Had one on NASA site. I used to make do with what I
had, and accuracy necessity, in a research design, and repIr shop.

Greg

[Shaun]

"Johnny Appleseed" <no...@nowhere.non> wrote in message
news:jq2qes$hn$1...@dont-email.me...

> I have a digital thermometer like the one here:
>
> http://www.walmart.com/ip/Acurite-Wireless-Thermometer/16888921
>
> The temperature the outdoor sensor reads is at least 3 degrees off from
> what it should be. Is there any way to adjust the temperature reading in
> these units? The instructions don't say anything about this issue.
>
> Thanks,
> John

You bought it at Wal-Mart and you're surprised that it is not accurate??
Duhhhhhhhhh!
3 degrees is not bad for something that sells for less than $10.00
stupid!!!

[hindsit...@sbcglobal.net]

I have an Acurite with outdoor sensor that I got as a gift. The indoor is right on, but the outdoor temp is 6-7 degrees LOW based on comparisons with multiple sources including another wired thermometer to the outside, also in the shade. That one always reads exact to my various other sources. It's just annoying and realize I should just replace it but Ive been looking for a weather station that gives me wind speed and direction and something of higher quality but not over 300 to 400$.

[mike]

On 12/31/2014 11:12 AM, hindsit...@sbcglobal.net wrote:
> I have an Acurite with outdoor sensor that I got as a gift. The indoor is right on, but the outdoor temp is 6-7 degrees LOW based on comparisons with multiple sources including another wired thermometer to the outside, also in the shade. That one always reads exact to my various other sources. It's just annoying and realize I should just replace it but Ive been looking for a weather station that gives me wind speed and direction and something of higher quality but not over 300 to 400$.
>

make sure your sensors are exactly in the same place and shielded from
the wind/sun etc when you compare.
It's noon.
Front sensor reads 34F
Side sensor reads 42F
Back sensor reads 38F
all are in the shade.
If I put them all in the same place at night,
they read within a degree of each other.

I have an Acurite remote thermometer. The clock loses about half
a minute per day. Looks like we agree they're crap.

Make darn sure you have a place to mount your weather station.
I got one on a whim at a garage sale cuz it was free.
Got it home and started looking where I'd mount it.
Turns that there's enough shadow from trees along the back
to block a significant portion of the rain.
And all the swirling from the trees made the wind speed
and direction just random numbers.
Glad I didn't pay $400 for it.

[Cydrome Leader]

hindsit...@sbcglobal.net wrote:
> I have an Acurite with outdoor sensor that I got as a gift. The indoor is right on, but the outdoor temp is 6-7 degrees LOW based on comparisons with multiple sources including another wired thermometer to the outside, also in the shade. That one always reads exact to my various other sources. It's just annoying and realize I should just replace it but Ive been looking for a weather station that gives me wind speed and direction and something of higher quality but not over 300 to 400$.

I use the cheapo radio shack indoor/outdoor thermometers and they drift as
well. When new, the outside probe and inside probe matched, but not
anymore. I think something happened with the insulation of the wire or the
sensor which is potted in a little probe.

[Maynard A. Philbrook Jr.]

In article <d176a781-a6bf-4ffe...@googlegroups.com>,
hindsit...@sbcglobal.net says...

>
> I have an Acurite with outdoor sensor that I got as a gift. The indoor is right on, but the outdoor temp is 6-7 degrees LOW based on comparisons with multiple sources including another wired thermometer to the outside, also in the shade. That one always reads exact to my various other sources. It's just annoying and realize I should just replace it but Ive been looking for a weather station that gives me wind speed and direction and something of higher quality but not
over 300 to 400$.

Put something over the sensor, maybe it has some self heating and the
wind chill, as little as it maybe is cooling it.

Jamie

[Jeff Liebermann]

On Wed, 31 Dec 2014 11:12:46 -0800 (PST), hindsit...@sbcglobal.net
wrote:

>I have an Acurite with outdoor sensor that I got as a gift.

Anything that claims to be amazing, magic, miracle, or accurate in the
name, probably isn't. Since you didn't bother providing a model
number, I'll assume you've already given up and are now shopping for a
$300+ weather station. I think you'll find that a decent weather
station (Peet Bros, Davis, etc) are far more expensive. $300 is about
the starting price for a bottom of the line Davis.

>The indoor is right on, but the outdoor temp is 6-7 degrees LOW based
>on comparisons with multiple sources including another wired thermometer
>to the outside, also in the shade. That one always reads exact to my
>various other sources. It's just annoying and realize I should just
>replace it but Ive been looking for a weather station that gives me
>wind speed and direction and something of higher quality but not over
>300 to 400$.

There's nothing wrong with the thermometer or sensor. The problem is
location, location, location, and ummm... location. I "manage"
several weather stations and have great difficulties getting
consistent temperature readings. There are standards for locating
sensors which must be followed. I need to run, so here are some
links. Bug me (or post to a weather newsgroup) if lost:

Data quality:
<http://www.wxqa.com/AllenFreeMetQC.pdf>

Citizens weather observer corp, which monitors temp sensor
consistency.
<http://www.wxqa.com>

Radiation shielding:
<http://wxqa.com/shields.html>

Siting:
<https://www.campbellsci.com/weather-station-siting>
<ftp://ftp.campbellsci.com/pub/outgoing/apnotes/siting.pdf>
<http://wxqa.com/resources.html>

gone...

[Jeff Liebermann]

On Thu, 01 Jan 2015 11:41:23 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

Blundering onward...

>Siting:
><https://www.campbellsci.com/weather-station-siting>
><ftp://ftp.campbellsci.com/pub/outgoing/apnotes/siting.pdf>
><http://wxqa.com/resources.html>

This one is quite good on siteing.
<http://weather.gladstonefamily.net/CWOP_Guide.pdf>

Basically, what you're missing with your unspecified model Acurite
weather station is a radiation shield for the temperature sensor. What
you're trying to do is measure the air temperature, not the
temperature of the plastic box, the nearby walls, exhaust vents,
parking lot heat island, reflections from low-e glass, foliage
transpiration cooling, and a zillion other sources of error. Here's a
fun example:
<http://802.11junk.com/jeffl/crud/KSBW-WX-Station.jpg>
That's the local radio station's weather sensor array on the left,
sited over the HVAC system.

More on badly located weather stations. This site is well worth
skimming:
<http://www.surfacestations.org>
Even the official weather stations are often badly located:
<http://www.surfacestations.org/odd_sites.htm>

This is one of my early attempts at a radiation shield (pagoda):
<http://802.11junk.com/jeffl/pics/wx/slides/radiation-shield-01.html>
It was ok, but I missed something obvious. There's a gap near the top
of the wall where the cable goes through. Inside the building are
several high power transmitters, which produce lots of hot air, that
greatly affects the indicated temperature. Here's the CWOP report on
temperature and barometric accuracy. The station was removed and is
being moved to a better location sometime in the next month.

Enough for now. Your problem will be:
1. Do some reading on proper weather station siteing and Stevenson
Screen radiation shield construction.
2. Find a better weather station if you want accuracy.
3. Register with the various amateur weather web sites (Weather
Underground, CWOP, etc and see if your numbers track those of the
stations around you.

[Sjouke Burry]

4,5 and 6:Put all your thermometers in one place,
to properly compare them.
8,9 and 10:Repeat that on the other side of the house.

[Jeff Liebermann]

On Fri, 02 Jan 2015 07:23:22 +0100, Sjouke Burry
<burrynu...@ppllaanneett.nnll> wrote:

>4,5 and 6:Put all your thermometers in one place,
> to properly compare them.

Much depends on the initial tolerance of the thermistor sensor.
Typically, a 1% thermistor is good for about 0.03 C error for the
thermistor alone, and about 0.5 C error if you include the associated
electronics. With a cold junction reference, 0.1 C is typical. If
the thermometer uses a 5% tolerance thermistor, just multiply
everything by 5. Note that the OP was complaining about a 6-7 degree
difference.

Details:
<https://learn.adafruit.com/thermistor?view=all>
See bottom of article for accuracy estimates.

>8,9 and 10:Repeat that on the other side of the house.

Reminder. The goal is to measure the temperature of the air, not the
room or building walls. Doing this test indoors is just asking for
complications due to stratification (it's warmer near the ceiling) and
the multitude of local heat sources found indoors. Isolating the temp
sensor from everything except the air is why real weather stations use
radiation shields.

The problem can be reduced by isolating the thermistor and using a fan
to blow air to the sensor. The design turns out to be fairly complex:
<http://www.davisnet.com/news/enews/images/1210SPARS.jpg>
I'm not a big fan (pun intended) of fan aspirated radiation shields,
but they do work (if you keep them clean).
<https://www.google.com/search?q=fan+aspirated+radiation+shield&tbm=isch>