I'm curious if anyone knows how the ds18b20 probes compare to a max31855 + k-type sensor setup for measuring water temperature around the freezing point of water? (or if anyone knows of a better solution)
I want to set up something to turn on a heat pad under a bird bath in cold weather.
SW
A DS18B20 will do just fine. No need for particularly high accuracy in an application like that.
The waterproof 18B20 might be good for that application.
If you do not have a waterproof sensor you can always pot it with RTV compound. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
A type K thermocouple is really only of use at high temperatures , the voltage it produces is related to the temperature difference of the measurement junction and the second junction formed where you connect it . A second different type sensor is used at this junction to “ add” the ambient temperature .
So with a 20c temperature difference you only get about 800micro volts from the output - difficult to get accurate results !
The Chinese ds1820 “ water proof” sensors usually aren’t, only the tip is waterproof .So you will need to fit it inside some form of sheath ( see thermowell ) . Make yourself an ice bath reference to calibrate and get things spot on . These sensors are easy to use and very stable .
Remember, only pure, distilled water will freeze at 0C. Tap water and bird bath water must be colder to freeze.
Paul
The difference in melting points may well be within the error of the DS18B20... so the bird bath may freeze as that probe still indicates a temperature of >0 C.