DIY auto draw

[4x4extreme]

I am thinking about making my own Barometric pressure compensating auto draw-off. I have been thinking about using a click PLC or a Arduino for the controller.
Have any of you guys used one of those for the controller?

I have been having trouble with the math. If I have a known barometric pressure what equation would I use to get the boiling point of water?


Thanks

[4x4extreme]

I have been using 49.161 x ln(known pressure)+44.92 but when I test it the temperature is to high.

[darkmachine]

Are you poling a barometric pressure sensor or just checking your math? check out the thread: Combining hobbies - atmospheric pressure compensating temperature device

I have an Arduino Metro barometric sensor, and thermocouple all soldered up, but waiting on winter break from school bus driving to start coding.

[4x4extreme]

The main thing I am trying to figure out is the math. I have been taking the known pressure and using a math equation I get a higher boiling point than when I test it.

[darkmachine]

So i checked your equation to calculate boiling at sea level, so this is what i plugged in. Barometric pressure was Inches of Mercury so 29.9212in/hg at sea level according to the internet.

(49.161 x ln(29.9212)) + 44.92 = 211.996965032

If you increase the precision of the 44.92 to 44.932 you will get 212.008965032

[wobbletop]

Boiling point of water vs pressure is not linear (but it might be close enough over the range you are looking for.

https://i.imgur.com/1n6Go4M.png

[4x4extreme]

Boiling point of water vs pressure is not linear (but it might be close enough over the range you are looking for.

https://i.imgur.com/1n6Go4M.png

I think that is why I am off at the boiling temp. I should have thought of that

[darkmachine]

I'm at about 1000ft above sea level and when I use the formula output to set my pid draw off temp for my altitude, it's very close, right on the line of my hydrometer.

[darkmachine]

50kpa is about 500 millibars according to google. 500 millibars is the pressure around 18000 feet right? Just some quick googling it's probably straight enough between 100 and 200 kpa. I doubt many are evaporating outside that range, could be wrong, lol

[4x4extreme]

I have just been testing the math with the Barometric pressure from accuweather and boiling water to see what I come up with.
Today pressure was 30.03 when using the equation I get 212.17° but If I boil water it will boil at 210.6°. I may go ahead and build it with a Arduino and try it this spring. If it works then great and if not I am not out much.

[darkmachine]

You need a barometer at your location. The closest weather station for AccuWeather to pull from might have different enough conditions to throw off your boiling temperature. Where are you in WV?

[minehart gap]

And how sure are you of the calibration of your thermometer?

[TapTapTap]

I have just been testing the math with the Barometric pressure from accuweather and boiling water to see what I come up with.
Today pressure was 30.03 when using the equation I get 212.17° but If I boil water it will boil at 210.6°. I may go ahead and build it with a Arduino and try it this spring. If it works then great and if not I am not out much.

You can't be taking an accurate temperature measurement.

ken

[4x4extreme]

And how sure are you of the calibration of your thermometer?

I had 4 of them in the water. 0ne candy 2 digital and 1 dial thermometer.

[4x4extreme]

You need a barometer at your location. The closest weather station for AccuWeather to pull from might have different enough conditions to throw off your boiling temperature. Where are you in WV? I am in Beckley. I am going to get a sensor so I can get the pressure for my location. I am also going to go ahead and get the parts to put this together with a arduino.

[TapTapTap]

I had 4 of them in the water. 0ne candy 2 digital and 1 dial thermometer.

Did you bring it up to a hard boil?

[4x4extreme]

Did you bring it up to a hard boil?

Yes I did this test for well over 30 minutes and even had to add water due to evaporation. I am just trying to test my equation to see if it is correct before putting it into the program. The first thing I have to get is a accurate pressure reading for my location. It has been throwing me off because I live just over 2400 ft elevation so when the equation is telling me boiling is over 212 that is a red flag.

[darkmachine]

I am in Beckley. I am going to get a sensor so I can get the pressure for my location. I am also going to go ahead and get the parts to put this together with a arduino..
I purchased all my parts through adafruit, BMP280 for my barometric sensor, and pt100 three wire thermocouple and amplifier. It's been sitting in my shop for a while, you are motivating me to get back to work! I'm in the eastern panhandle quite a drive from Beckley.

[minehart gap]

I had 4 of them in the water. 0ne candy 2 digital and 1 dial thermometer.
That's impressive. I have gathered quite a collection of thermometers, some really high quality and some not so great, and I seldom get two to agree to the tenth of a degree. Sounds like an interesting project.