Hi all,
I’m looking for recommendations for a temperature sensor to be used in a marine fish tank
I currently have a DS18B20
Is there maybe another temp sensor that can be accurate to 0.1 C?
It needs to submersible and fairly corrosion resistant
DS18B20 in 12 bit mode?
Hi!
What kind of ref voltage do You use? That is important. Check Youtube for educating videos!
An absolute accurasy of 0,1 degree calls for precision from top to bottom.
Differential measurements can use almost any ref and sensor.
Know that resolution and accurasy are two totaly different questions.
Railroader:
Hi!
What kind of ref voltage do You use?
The DS18B20 is a digital device.
Resolution of the DS18B20 is 0.0625C.
Default factory callibrated accuracy is 0.5C.
YOU can further calibrate that to 0.1C by adding an offset to the readout.
Leo..
YOU can further calibrate that to 0.1C by adding an offset to the readout.
Which of course requires access to a thermometer that is calibrated to at least that level itself, as otherwise you have the precision, but not the accuracy.
Without calibration you can of course still use it to see stability of the temperature, as while the absolute value will be a little off, the relative changes will be very accurate.
There are a number of ±0.1°C temperature sensor modules at tindie.com
This is one of them: https://www.tindie.com/products/closedcube/si7051-01c-max-digital-temperature-sensor/.
wvmarle:
Which of course requires access to a thermometer that is calibrated to at least that level itself, as otherwise you have the precision, but not the accuracy.
Or a bucket of ice water and a pot of boiling water. (the boiling water measurement requires adjusting for altitude / barometric pressure)
Also make sure it's distilled water for both ice and boiling water, or you're off due to the dissolved mineral salts (lower melting point and higher boiling point). You don't need much minerals to get 0.1 degree change there.
The melting ice is the easiest, and a single calibration point should give you a pretty good correction already.
I have seen MANY posts over the last 6-7 years stating that the DS18B30 is the one to get if you want accuracy. The DS18B20 is pay-for-what-you-get cheap.
PS -- I tried to remember the degrees C increase in boiling point per mole of salt added to a liter of water but that was a long time ago so I looked it up. While the entire subject is loaded with conditions the basic idea of common minerals in water can be ballparked.
For saltwater, the boiling point is raised, and the melting point is lowered. By how much depends on how much salt there is. I’ll assume the salt is sodium chloride, NaCl (table salt). The melting point is lowered by 1.85 degrees Celsius if 29.2 grams of salt are dissolved in each Kg of water (called a "0.5 molal solution" of salt. The Na and Cl dissociate right away when dissolved, and so for a 0.5 molal solution of salt, there is a 1.0 molal concentration of ions). The boiling point is raised by 0.5 degrees Celsius for water with 29.2 grams of salt dissolved in each kg of water.
An ounce of salt per a liter of water is nothing like what comes out of my tap. I get trace minerals, some lead, mining tailing leachings and used fracking chemicals in my city water.
Hi,
Why do you need 0.1C accuracy, the thermal gradient across/through your tank will be greater than that.
The worlds tropical oceans do not have critters in them that need that level of control.
Tom... 
I think there are a lot of cheap out there , I have two versions here , with the same code one has a resolution of .1 the other is .5
so one must be limited in hardware to 8 bits ??
I only noticed this when I added a new sensor to the hot tub project, checked the display and it was showing in .5 steps, at first I re checked my code, then I replaced the sensor with the original, it was the sensor
The resolution of a DS18B20 can be changed.
http://www.homautomation.org/2015/11/17/ds18b20-how-to-change-resolution-9101112-bits/
Leo..