I need an accurate thermometer for my research (-10~110 C), because the commercial ones are not programable . I would like to have a +-0.001 C accuracy one (maybe it is not possible at all ). But after checking around, all I have found are at best +-0.1 one (tmp117). I found some with 24bit ADC in it but only claim +-0.1 C accuracy ( TSYS01), which confuses me quite a lot, why a 24bit ADC can only achive a +-0.1 C accuracy?
Then I think it might be a good idea to build one. I have chosen a good NTC thermoresistor and a good 24bit ADC. What else do I need ? Maybe need a good bridge circuit to read the value of the NTC resistor and a stable voltage reference? Any better idea?
Note the reading doesn't have to be very fast. 0.24 Hz final reporting rate is fine.
So far the best commercial one I have found is this:
maybe I made a misleading statement, I meant I would like to make it (the whole system) as accurate as possible, I was considering something like PT100. But I found even an A+ grade one could not do that. Plus, a small value resistor like the pt100 makes it very sensitive to the accuracy of the other resistors in the circuit.
Since I don't need this thing to be super fast. I guess I can read the NTC fast and average the readings. As long as the repeatability of this NTC is good, I can get something close.
0.001 degree means I just want to make it as best as I can do. It doesn't have to be 0.001, it can also be 0.00001 if it is easier
It is about molecular behavior. My teacher told me to do so... And he said the budget is not a problem. But I think he means if I can make one he will buy the parts for me, not the commercial ones....
It is not a request Paul. It is just a discussion. Maybe I underestimated the challenge of the accuracy of this measurement, but the world is making its progress. Even the expected goal is not possible today, doesn't mean it is not achievable at all. After all it is not against the 2nd law of thermoal dynamics.
Why am I here? I think the reason I am here is the same as the reason of a lot of other people. Even the queastion I asked is naive, it still has its value. Other people later can check the result of this thread and save time on their similar project. I think that is part of the spirit of opensouce hardware, isn't it?
My impression of arduino platform is that it can do a lot things, together with other circuits, it can do almost anything other mcu based systems can do.
The OP has only said it is about molecular behaviour.
@joedodo if you wouldn't have to kill us for having done, please tell us more about what things you are measuring the temperature of exactly, and the physical circumstances in which they find themselves.
Are these temperatures typically measured by any pedestrian devices like you are thinking about? Sounds more involved, like real scientists determine temperatures of molecules in a totally different way. About which I know nothing, but probably not a meat thermometer, even if it could do 0.001 degree.
I would like to have a +-0.001 C accuracy one (maybe it is not possible at all ).
Of course it is possible, you just have not looked very hard.
You pay for accuracy, because someone has to calibrate each instrument against a certified standard.
As a very rough guide, cost goes up by at least a factor of ten for each factor of ten improvement in accuracy. So, if a $100 thermometer is certified for +/- 0.1 C, expect to pay $10-100K for +/- 0.001 C.
Yes. I am checking out the IR solution, too. Yes, I care about the variation more than the absolute value.
Thanks for the constructive reply The reason I would like to choose arduino over the commercial ones for this is exactly its flexibility. I do expect the algorithm part and the control part of this system are complex.
NTC's are not that stable. Even if you could calibrate it to some better thermometer they will not maintain the stability you request (not even close).
The best thermal resistor you can purchase (reasonably) is a Platinum Resistor usually P100 (could be P500). Google them.
At the same time you should get a good understanding or accuracy, resolution, repeatability and perhaps hysteresis.
The accuracy your request also requires a considerable amount of physical application effort. If you were actually able to measure to within 0.01 °C you still have to deal with thermal lag in the sensor and maybe the medium. You will be hard pressed to hold anything to within 0.01°C long enough to take a measurement.
Before you start your research you should go through a statistic analysis of your possible readings/results and see what you need to actually make you results statistically significant.
I've done this in the past but don't recall the approach I used.
which confuses me quite a lot, why a 24bit ADC can only achive a +-0.1 C accuracy?
thanks John for your insight. Initially I would like to choose NTC is because of its relatively large resistance (~10k). This resistance makes the wire resistance less important and makes the design easier. Now maybe I will start using pt100/1000 series.
The one I mentioned with a 24bit adc in it is TSYS01. I wonder why it claims only 0.1 c accuracy. Maybe just because it has not been calibrated to a better one? Or maybe the resistor component in it is not stable/repeatable enough to achieve a better one.
That’s why I introduced the idea of using start-finish calibration set points, then tracking the relative variation over time.
It’s certainly not a simple question, and I doubt it’s going to be cheap, but the Arduino will likely be the least of your problems!
Up above, others have suggested the precision probes are out there, but I suspect most of us have never - if ever needed better than 0.1C absolute resolution.
I’m sure we can help - once you’ve identified a sensing mechanism.
The reason I would like to choose arduino over the commercial ones for this is exactly its flexibility. I do expect the algorithm part and the control part of this system are complex.