Electronics > Metrology

Questions on pt100 probes

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mendip_discovery:
Too many variables with the boiling water technique.

What I have is a dry block calibrator and that is fairly good at holding temperature. But I use a master probe that is known and I can use that for the temperature. Expect me to revise this over the next year or so as I delve into the world of temperature.

ap:
Building a gallium cell may also be an option for you...

BarrowBoy:

--- Quote from: ap on July 13, 2024, 02:30:15 pm ---Building a gallium cell may also be an option for you...

--- End quote ---

Unlikely..lol. Nice website BTW.


--- Quote from: Yuu on July 12, 2024, 06:26:17 pm ---
--- Quote from: BarrowBoy on July 09, 2024, 11:42:24 pm ---If range is 0-100C, then any reason a Thermistor is not being used? They have a far greater value change across their working range and are very good in this temperature range IMO. Below is something I found online which is a good summary of why I ask.

--- End quote ---

No reason in particular. The pt100 stuff is just what I stumbled into learning about atm.
For my temp range, could a thermistor be more accurate? (yes I know an RTD is a type of thermistor technically but it's my understanding that thermistors in this context are typically semiconductor material with a negative temperature coefficient)
If so, any recommendations for like a stainless-steal-sheath probe preferably under $100?

I'm willing to bet, for this temp range, accuracy of thermistors and pt100 probes are comparable and it more primarily depends on how much you're willing to spend.
Like I think Fluke sells both types of probes with pretty darn good accuracy but they're expensive lol.

--- End quote ---

It's actually a recommendation I was given by Fluke. Well not really Fluke, more their division based in Salt Lake City, formally known as Hart Scientific. Bang for Buck, it's a Thermistor solution. But over over 100C, or below TPW, and you need RTDS.  Here is a link for their premium Thermistor probes. Note the text at the foot of page. Also often thermistors are preferred due to their rate of change over the 0-100C span, but they can by design  a small sensor, with very fast settling time / stability, and very little stem convection, which improves accuracy when measuring and ease for calibration.

https://www.fluke.com/en/product/calibration-tools/temperature-calibrators/fluke-hart-secondary-thermistor-probes

Also this article may help, differs a bit from my advice on range, it notes (-80C thru +150C) which is news to me, but hey were here to learn ;)

https://www.analog.com/en/resources/analog-dialogue/articles/thermistor-temperature-sensing-system-part-1.html

mzzj:

--- Quote from: jchw4 on July 13, 2024, 10:37:21 am ---BTW, could somebody suggest how to do a boiling water test? It feels way more complicated than the ice bath, but I was thinking of maybe getting current air pressure at my place from weather.com and adjusting readings to the boiling temperature table that I can probably find online.

Does it make sense to try that?

--- End quote ---
Bit late to the party but for anyone interested try digging old NIST documents. Previous temperature scale IPTS-68 (used up to 1990) was based on water boiling point and some laboratories had specific apparatus for water boiling point calibration.
IIRC you can't immerse the thermometer to boiling water, instead you need to form closed space for the steam to collect and heat up the thermometer with the steam.

And be vary of the air pressures. Most weather services and all airports give you "sea level adjusted" barometric pressure that can be totally different from true air pressure.
An extreme example would be  Albuquerque https://photovoltaics.sandia.gov/weather/Weather.htm

MiDi:

--- Quote from: jchw4 on July 13, 2024, 10:37:21 am ---BTW, could somebody suggest how to do a boiling water test? It feels way more complicated than the ice bath, but I was thinking of maybe getting current air pressure at my place from weather.com and adjusting readings to the boiling temperature table that I can probably find online.

Does it make sense to try that?

--- End quote ---

As for ice bath you need pure water e.g. deionized (standard labs use VSMOW2), an accurate abs. pressure sensor e.g. BMP581 and the calculator coolprop for BPW at the measured pressure.

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