Author Topic: Looking for a simple, reliable, way to calibrate temps  (Read 897 times)

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Offline DaleReid

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Looking for a simple, reliable, way to calibrate temps
« on: May 13, 2017, 05:03:33 PM »
I have numerous stations and temp indicators about the property here and at a couple friends who suffer me their places to monitor.

Today, as an example, I ran across the amateur's nightmare again... Is my temperature sensor calibrated?

I have mercury thermometers like the old Taylor U shaped tube with the magnet to reset the max and minumum.  One might think that when both the scales are adjusted to read the same that all would be well.  Dunno.

I have Davis, which everyone says are pretty good from the factory, and argue over aspirated vs. none.

I have a few mercury thermometer Taylor Sling pychrometers, and with two thermometers that sort of read the same, that's reassuring, but it is still not a standard.

Today the problem came up as I'm finishing getting all the parts together and running barometer tracking and such before putting the unit out.

For those who're not familiar, the Texas Wx Instruments WRL-25 has a remote 'pagoda' that is basically a radiation shield with the temp/humidity sensor inside.  It also comes with an indoor temp sensor, a little something like a thermistor on the end of a two foot flexible cord.  My simplistic way of thinking is to stick the flexible cord tip up inside the pagoda to about where the sensor should be, and let things run a few days.  Sometimes the temps close, but usually 3/4 to 1.4 degrees apart. 

Each readout (in tenths) can be tweaked individually in the console. 

Problem... which one, if either, is closest to the 'right' temperature?  I have a larger temp unit that won't slip up inside the pagoda to add another number to the mix.  I have a single mercury thermometer which being glass and long and inflexible, has the same problem.  I've taken an IR meter and measured temps off the surface of the pagoda, but of course that gives once again the surface temperature, even in my work area in the basement where the sunshine doesn't hit.

I could immerse the flexible 'indoor' probe in the ice bath trick for awhile, see if I can get it close to 32, and then stuff it back in the pagoda for a day or two to see if I can make the outside sensor track, too.

Or, if someone knows of a handy-dandy pretty darn accurate ( from say 32 up to 100 F) portable hand held system with a little probe that also could go up in close proximity with the other sensors, I could try using that, not only for this project, but everything else.

I was at the drug store and looked at little oral and rectal battery powered thermometers, but they are limited to a few degrees around what us humans usually maintain.

I looked at the kitchen supply store for a kitchen thermometer which also includes room temperature ranges in addition to cooked meet temps, but wouldn't you know,they all allow adjustment, so what is a good standard?

I'm not doing research, but would like to report to the local nets when I did hit freezing or was a couple degrees above at the location of the sensors. 

Any thoughts?

Dale
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Offline CW2274

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #1 on: May 13, 2017, 05:50:22 PM »
PM ValentineWeather, I know he has a NIST traceable one accurate to 0.01F I believe, that you can compare with your sensors. I looked for it, but no joy.
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Offline DaleReid

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #2 on: May 13, 2017, 06:19:30 PM »
Thanks, I knew someone had discussed but didn't find the right keyword for search I guess .  Im off to discover. Thx.
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Offline ValentineWeather

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #3 on: May 14, 2017, 06:08:09 PM »
Answered PM, Cole parmer is what they were called. Can't find same units anymore I've tried before and just looked again.  They had 3 different certifications 0-20-40C I believe. Mine are expired in 2015 but they are still good enough. Accuracy was something like .01.
« Last Edit: May 14, 2017, 06:09:41 PM by ValentineWeather »
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Offline DaleReid

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #4 on: May 14, 2017, 06:19:40 PM »
Thanks for your prompt reply, and unfortunate news they may no longer be available.

But the way today is going, sort of par for the course.

Thanks again.  I'll go looking for something and let the thread know if I find anything.
Dale
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Offline CW2274

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #5 on: May 14, 2017, 06:35:45 PM »
Found it, or at least something similar. Only problem it's ~3x more expensive than the one Randy bought, IIRC.
https://www.coleparmer.com/i/digi-sense-4000ds-usb-calibrated-scientific-thermistor-thermometer-usb-probe/9008009
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RW Tipper w/ CoCoRaHS

Offline ValentineWeather

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #6 on: May 14, 2017, 07:07:07 PM »
Found it, or at least something similar. Only problem it's ~3x more expensive than the one Randy bought, IIRC.
https://www.coleparmer.com/i/digi-sense-4000ds-usb-calibrated-scientific-thermistor-thermometer-usb-probe/9008009

Way over priced. In 2013 seems they ran $85-100.
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Offline CW2274

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #7 on: May 14, 2017, 07:07:55 PM »
How much is an accurate, old-fashioned, mercury/alcohol glass-stem thermometer?
Very, if a good one. The problem I see is that the response time would be a century compared to a digital sensor, and also lack of resolution.
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Offline CW2274

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #8 on: May 14, 2017, 07:10:17 PM »
Found it, or at least something similar. Only problem it's ~3x more expensive than the one Randy bought, IIRC.
https://www.coleparmer.com/i/digi-sense-4000ds-usb-calibrated-scientific-thermistor-thermometer-usb-probe/9008009

Way over priced. In 2013 seems they ran $85-100.
But the thing is the claimed accuracy is over the entire 0-100c range, unlike what you bought, if I understand yours right.
Davis Wireless VP2 SHT31 24hr 67CFM FARS
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Offline CW2274

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #9 on: May 14, 2017, 07:15:16 PM »
You saying ALL those readings they made in the past aren't really that accurate (wink,wink)?
It only has to be accurate to ONE decimal place for our data.
I still think an accurate comparison would pretty much have to be digital to digital and analog to analog.
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline ValentineWeather

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #10 on: May 14, 2017, 07:17:37 PM »
How much is an accurate, old-fashioned, mercury/alcohol glass-stem thermometer?

Tom Skilling, chief meteorologist at WGN-TV says .2F.

 http://articles.chicagotribune.com/2000-05-28/news/0005280042_1_thermometers-readings-accurate
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Offline ValentineWeather

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #11 on: May 14, 2017, 07:19:43 PM »
Found it, or at least something similar. Only problem it's ~3x more expensive than the one Randy bought, IIRC.
https://www.coleparmer.com/i/digi-sense-4000ds-usb-calibrated-scientific-thermistor-thermometer-usb-probe/9008009

Way over priced. In 2013 seems they ran $85-100.
But the thing is the claimed accuracy is over the entire 0-100c range, unlike what you bought, if I understand yours right.

Okay then mine were only guaranteed within 5 range of certified point. 
Randy, the Aviator is my father in 1963 with his Indian bike

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #12 on: May 16, 2017, 09:51:17 PM »
I recently received this: http://www.novatech-usa.com/Products/Min-Max-Thermometers/6410. It's NIST certified to within 0.1 deg Celsius (0.18F) from -148 to 199F. I've got the paperwork to prove it.

I used it on my Davis VP2 SHT31 sensor. I took 4 samples over different times of day and night, even going so far as removing the ISS from its post and taking both instruments into the garage to control for solar radiation (and allowing both sensors to acclimate for about 30 minutes before taking a reading). After averaging all the samples (ranging from 0.3 - 0.5F), I applied a -0.4F offset in my console.

If I had to do it over again, I'd probably just order the calibration thermometer directly from the manufacturer, Control Company, who sells it for about $20 more. Why? Because Nova Tech thought it was cool to just let their customer hang out to dry with no word on status for 2 weeks while they quietly back ordered it. I had to chase them down just to get a status. The reply I received was curt. Not cool. Apparently, I've been spoiled by Ryan's good customer service at Scaled Instruments. Sadly, he does not carry anything like this.
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Offline DaleReid

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #13 on: May 16, 2017, 10:20:10 PM »

I'll send him a note to ask. Thx. And thanks for all the comments. Dale
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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #14 on: June 23, 2017, 09:44:55 AM »
Dale, was Ryan able to get you what you needed? Were you able to calibrate your equipment?
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Offline DaleReid

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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #15 on: June 23, 2017, 10:02:21 AM »
He didn't have anything like that in his stock, nor was he thinking that the quantities he'd have to stock would move fast enough.  He gave me some hints.

I have looked at a couple of items and one that has been used by one of the members here, and so far, have been busy with a few 'unexpected' challenges that I'd not have gotten around to doing a calibration even if I had the tool.  I think this will become a late summer project right now. 

Did you have any experience with calibrations?
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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #16 on: June 23, 2017, 10:07:55 AM »
I recently received this: http://www.novatech-usa.com/Products/Min-Max-Thermometers/6410. It's NIST certified to within 0.1 deg Celsius (0.18F) from -148 to 199F. I've got the paperwork to prove it.

I used it on my Davis VP2 SHT31 sensor. I took 4 samples over different times of day and night, even going so far as removing the ISS from its post and taking both instruments into the garage to control for solar radiation (and allowing both sensors to acclimate for about 30 minutes before taking a reading). After averaging all the samples (ranging from 0.3 - 0.5F), I applied a -0.4F offset in my console.


The trick is to remove solar radiation from the equation. I did my calibrations at night and also in the garage during the daytime.
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Re: Looking for a simple, reliable, way to calibrate temps
« Reply #17 on: June 23, 2017, 10:24:29 AM »
Did you have any experience with calibrations?

In answer to your question, not formally or professionally.  Just a science and technology enthusiast (nerd).
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