I have tried DS18B20, LM34, MAX31855.... they don't work - I get random readings no matter what.
Tried different boards Uno, Mega, STM, ESP32.
Everytime I get different bad readings. Maybe all those circuits are bad or defective....
All I want to do is measure temperature with low degree values - like going to -100C. Range let's say -200~200C
What is the best temperature sensor and thermocouple for that? What would you recommend?
Thanks
Deous:
I have tried DS18B20, LM34, MAX31855.... they don't work - I get random readings no matter what.
Tried different boards Uno, Mega, STM, ESP32.
Everytime I get different bad readings. Maybe all those circuits are bad or defective....
More likely: you do something wrong, or you use the sensors out of their range.
All I want to do is measure temperature with low degree values - like going to -100C. Range let's say -200~200C
What is the best temperature sensor and thermocouple for that? What would you recommend?
NTC.
Deous:
I have tried DS18B20, LM34, MAX31855.... they don't work - I get random readings no matter what.
Tried different boards Uno, Mega, STM, ESP32.
Everytime I get different bad readings. Maybe all those circuits are bad or defective....
All I want to do is measure temperature with low degree values - like going to -100C. Range let's say -200~200C
What is the best temperature sensor and thermocouple for that? What would you recommend?
"they don't work" and "random readings" and "different bad readings" is not very helpful.
Be specific.
The DS18B20 is a very stable and easy to use sensor, with high (0.0625°C) resolution, and factory calibrated to 0.5C.
But like all semiconductor based sensors, it has a limited temp range (-55 to +125C).
The LM34, and other analogue sensors (LM35, TMP36), have a similar temp range,
but could have a much lower resolution if read with Arduino's 10-bit A/D.
The wrong code could also make readings of those analogue sensors instable,
and factory calibration of analogue sensors in general is meaningless. You must calibrate yourself.
NTC (thermistors) could have a wider temp range than the above sensors, but resolution varies over that range.
Higher in the middle, and lower at the extremes. You need to calculate that to see if that's a problem or not.
And Arduino's default 10-bit A/D could also be a problem.
PTC sensors (PT100 platinum RTD) are probably the best choice for a temp range of -200C to +200C.
But they need a special preamp+A/D to be useful (MAX31865).
Tell us why you need a 400C span, and what resolution you expect.
Leo..
I am working on AC cooling project and maybe liquid nitrogen, R410a, R22 temperature measurement.
That doesn't explain why you need a single sensor to do -200 to +200C. That just shows you more likely need a number of different sensors, each tailored to it's own range.
For accuracy: if you're doing say liquid nitrogen, I'd want a sensor that's accurate between -170C to -220C- around the -196C boiling point of the stuff. If that sensor shows a temperature of +20C but is 10C off at that temperature I wouldn't care too much because it's obvious that your nitrogen has evaporated by then and there's nothing to measure anyway.
For the room temperature: use the common DS18B20 or similar. It will also do quite well to measure the temperature at the hot end of an AC compressor.
For the stuff that's normally at high temperature: get a thermocouple.
There are very few applications where you would have a point that goes through that great temperature swings, and where you really need to accurately measure the temperature over that full range.