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any way to calibrate digital thermometer?
I have a digital thermometer like the one he
http://www.walmart.com/ip/Acurite-Wi...meter/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 |
any way to calibrate digital thermometer?
Make a calibration chart.
|
any way to calibrate digital thermometer?
On Tuesday, May 29, 2012 8:36:59 AM UTC-7, Johnny Appleseed wrote:
I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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. |
any way to calibrate digital thermometer?
On Tue, 29 May 2012 11:36:59 -0400, "Johnny Appleseed"
wrote: I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
any way to calibrate digital thermometer?
On 5/29/2012 9:04 AM, nesesu wrote:
On Tuesday, May 29, 2012 8:36:59 AM UTC-7, Johnny Appleseed wrote: I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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. |
any way to calibrate digital thermometer?
Jeff Liebermann wrote:
On Tue, 29 May 2012 11:36:59 -0400, "Johnny Appleseed" wrote: I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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." |
any way to calibrate digital thermometer?
http://www.harborfreight.com/non-con...ter-93983.html
Just posted as an aside. I am amazed at how well the cheap ones work. |
any way to calibrate digital thermometer?
On Tue, 29 May 2012 15:45:59 -0700, John Robertson
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 # http://www.LearnByDestroying.com AE6KS |
any way to calibrate digital thermometer?
On Tue, 29 May 2012 19:11:25 -0400, "Charles"
wrote: http://www.harborfreight.com/non-con...ter-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. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
any way to calibrate digital thermometer?
"Johnny Appleseed" I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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 |
any way to calibrate digital thermometer?
Jeff Liebermann wrote:
On Tue, 29 May 2012 19:11:25 -0400, "Charles" wrote: http://www.harborfreight.com/non-con...ter-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 |
any way to calibrate digital thermometer?
"Johnny Appleseed" wrote:
I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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 |
any way to calibrate digital thermometer?
In article ,
"Johnny Appleseed" wrote: I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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. 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 |
any way to calibrate digital thermometer?
Jeff Liebermann wrote:
On Tue, 29 May 2012 15:45:59 -0700, John Robertson 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... 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." |
any way to calibrate digital thermometer?
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? |
any way to calibrate digital thermometer?
"William Sommerwerck" wrote in message ... 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. |
any way to calibrate digital thermometer?
"Gareth Magennis" wrote in message
... "William Sommerwerck" wrote in message ... 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? |
any way to calibrate digital thermometer?
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. |
any way to calibrate digital thermometer?
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. So I take it that, over the years, you have learned nothing new about problem solving from me? That's a shame. |
any way to calibrate digital thermometer?
On Tue, 29 May 2012 22:00:36 -0700, John Robertson
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. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
any way to calibrate digital thermometer?
Jeff Liebermann wrote:
On Tue, 29 May 2012 22:00:36 -0700, John Robertson 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! 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." |
any way to calibrate digital thermometer?
On May 30, 1:06*pm, John Robertson wrote:
Jeff Liebermann wrote: On Tue, 29 May 2012 22:00:36 -0700, John Robertson 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! 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."- 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. |
any way to calibrate digital thermometer?
On 5/30/2012 11:06 AM, John Robertson wrote:
Jeff Liebermann wrote: On Tue, 29 May 2012 22:00:36 -0700, John Robertson 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! 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. |
any way to calibrate digital thermometer?
On Wed, 30 May 2012 11:06:43 -0700, John Robertson
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 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
any way to calibrate digital thermometer?
On Wed, 30 May 2012 13:02:53 -0700, mike 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. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
any way to calibrate digital thermometer?
In article ,
Jeff Liebermann wrote: On Wed, 30 May 2012 11:06:43 -0700, John Robertson 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 |
any way to calibrate digital thermometer?
In article , mike
wrote: On 5/30/2012 11:06 AM, John Robertson wrote: Jeff Liebermann wrote: On Tue, 29 May 2012 22:00:36 -0700, John Robertson 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! 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. The friendly folks at the local airport will do that for you, and put the results on the internet ... Isaac |
any way to calibrate digital thermometer?
On Wed, 30 May 2012 21:40:45 -0700, isw 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. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
any way to calibrate digital thermometer?
On 5/30/2012 9:18 PM, Jeff Liebermann wrote:
On Wed, 30 May 2012 13:02:53 -0700, 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. |
any way to calibrate digital thermometer?
On Tue, 29 May 2012 11:36:59 -0400, the renowned "Johnny Appleseed"
wrote: I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
any way to calibrate digital thermometer?
Spehro Pefhany wrote:
On Tue, 29 May 2012 11:36:59 -0400, the renowned "Johnny Appleseed" wrote: I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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 |
any way to calibrate digital thermometer?
gregz wrote in
rg: Spehro Pefhany wrote: On Tue, 29 May 2012 11:36:59 -0400, the renowned "Johnny Appleseed" wrote: I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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 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 |
any way to calibrate digital thermometer?
Jim Yanik wrote:
gregz wrote in rg: Spehro Pefhany wrote: On Tue, 29 May 2012 11:36:59 -0400, the renowned "Johnny Appleseed" wrote: I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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 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) 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 |
any way to calibrate digital thermometer?
"Johnny Appleseed" wrote in message ... I have a digital thermometer like the one he http://www.walmart.com/ip/Acurite-Wi...meter/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 $10.00 stupid!!! |
any way to calibrate digital thermometer?
I have an Acurite with outdoor sensor that I got as a gift. The indoor is right on, but the outdoor temp is 6-7 degrees LOW based on comparisons with multiple sources including another wired thermometer to the outside, also in the shade. That one always reads exact to my various other sources. It's just annoying and realize I should just replace it but Ive been looking for a weather station that gives me wind speed and direction and something of higher quality but not over 300 to 400$.
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any way to calibrate digital thermometer?
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any way to calibrate digital thermometer?
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any way to calibrate digital thermometer?
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any way to calibrate digital thermometer?
On Wed, 31 Dec 2014 11:12:46 -0800 (PST),
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 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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