No need to make it overly complicated if you don't work in primary laboratory with 10000 eur SPRT's
Properly prepared ice-water bath is easily better than 0,005 Cel accuracy and with some care 0,002Cel accuracy is quite possible. All you need is 10 eur thermos flask and 1 eur worth of distilled water. (ok, also some means to freeze the water but most of us have freezer)
+1
I don't have access to any serious gear, but a few years ago I bought a 4-ch Omega thermometer from ebay for $20 (with thermocouples and case!).
So I decided to do an ice test. I looked at a Fluke youtube video about their lab and how they make their triple cells and decided to do some quick and dirty first experiment before trying to make distilled ice and so on.
I had:
- ~0.5L Thermos flask that I received as a swag (you can order these for $10 now starting from 1 item with custom labelling included!). Cannot be cheaper.
- Tap water.
- Tap water ice from the ice generator in my fridge. I guess most modern US fridges have it.
- 4 straws that I could fit my thermocouples. I terminated one end with some glue.
I just filled the flask to the top with ice, inserted straws and filled the rest with water. I also made some foam "lid" out of some random piece that I had around. I was afraid that it could freeze immediately because of the -18C in the freezer, but looking at the log it never happened.
So you can see that it went to zero in about 15 minutes. Note that thermocouples were sitting in an air-filled straws.
The log had all zeroes for about 6 hours, but then it went up 0.2-0.3 C . I guess that I incerted them too deep. Next day (~18 hours after start) I pulled straws up and it went back to 0 C for another 15 hours! So if I had not put the straws too deep, I could have 2 full days of 0C !
Note that even though the meter has specified accuracy of +/-1C and resolution of 0.1C, it stayed at 0.0...0.1 C for many hours!
After that I never tried going deeper with distilled water, proper ice/water balance and everything elese you see on youtube.
Just try yourself with the regular water and maybe adjust your experiment later if your gear has better stability than the simplest ice bath
Mine is clearly not good enough for that.
But if you post your results here, experienced folks could probably help you with improvements.