any way to calibrate digital thermometer?

Make a calibration chart.

hat=20

e=20

John, if you can open the outdoor unit, look and see if there is any tiny p= otentiometer inside. It is likey that the calibration resides with the anal= og sensor before the signal is digitized for transmission. If there is a po= t [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 origina= l and live with it.

Neil S.

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:

Here's one that I help maintain:

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:

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.

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     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com

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.

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.

...

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).

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

John :-#)#

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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.

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.

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558

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.

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558

"Johnny Appleseed"

** 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.

** Have look inside yours.

The non radio linked kind generally have no adjustments.

... Phil

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

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

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

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

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

John :-#)#

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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?

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.

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.

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?

No, I do not know everything.

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

Gareth.

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

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.

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.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com

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 :-#)#

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