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any way to calibrate digital thermometer?

M

mike

Jan 1, 1970
0
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

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.
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.
 
P

Phil Allison

Jan 1, 1970
0
"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
 
G

gregz

Jan 1, 1970
0
Johnny Appleseed said:
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

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
 
W

William Sommerwerck

Jan 1, 1970
0
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?
 
W

William Sommerwerck

Jan 1, 1970
0
Gareth Magennis said:
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?
 
W

William Sommerwerck

Jan 1, 1970
0
You would do well to pay attention to this "knob".
No, I do not know everything.
I do know that you are a bit of a knob, though.

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

mike

Jan 1, 1970
0
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!

John :-#)#
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.
 
M

mike

Jan 1, 1970
0
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.
 
S

Spehro Pefhany

Jan 1, 1970
0
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
 
G

gregz

Jan 1, 1970
0
Spehro Pefhany said:
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
 
S

Shaun

Jan 1, 1970
0
Johnny Appleseed said:
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!!!
 
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