[time-nuts] Re: Long term stable environmental sensors

[Bob kb8tq]

Hi

If you have a giant pile of bonus points on your credit card, you can go investigate 
a “chilled mirror hygrometer”. There are a variety of brands. They all attempt to get
around the drift issue by taking it all back to dew point and thus a temperature reading. 
They are very expensive and I’m sure there are subtle issues with them ( maybe 
keeping the mirror clean ….who knows ). 

For pressure, the local airport might be an adequate substitute. A lot depends on just 
how much your building self pressurizes and how far that airport is from you. Building
issues can be addressed to some degree with a differential (indoor / outdoor) measurement.
Those are pretty easy to calibrate with a tube of water. 

Bob

> On Nov 29, 2022, at 4:01 AM, Attila Kinali via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Moin,
> 
> I have been monitoring my lab with a homebrew sensor board based on a BME280
> combined temp/hum/pressure sensor from Bosch. Unfortunately, the sensor seems
> to have quite some drift. Now, 4 years later, one of them shows 30°C when
> every other thermometer in the room shows ~22°C. And as temperature is
> needed to for compensation of the other measurements, I can't trust those
> either.
> 
> So, now I'm about to design and build a new system that has better long
> terms stability.
> 
> At the moment I think I will go with separate sensors for temp, humidity
> and pressure. Temperature is "easy", a PT100 will do the job nicely.
> For humidity, there is the SHT line from Sensirion that is well known.
> But I don't know of any decent absolute pressure sensor that is long-term
> stable and doesn't cost an arm and a leg.
> 
> Does someone know a pressure sensor that is long-term stable?
> 
> 				Attila Kinali
> 
> -- 
> The driving force behind research is the question: "Why?"
> There are things we don't understand and things we always 
> wonder about. And that's why we do research.
> 		-- Kobayashi Makoto
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