Hi Going back a bit to get closer to the original request …..
Indeed a thermistor is the “high resolution” king of the hill when it comes to temperature measurement. Resistance change of 3% (30,000 ppm) per degree is not uncommon, you can do better … They come in all sorts of packages for not a lot of money. eBay will happily supply you with a ton of parts. Go with high resistance parts to reduce the self heating issues mentioned below …. Since the original request was not concerned about accuracy ( only resolution) the cheap glass body eBay parts may do just fine. You would need to do a bit of characterization / curve fitting to work out what’s what. If you are after 0.001C resolution you would need to measure resistance to 30 ppm. That can be done. Indeed a bridge setup and looking at voltage is a more normal way to do this. For narrow ranges an op-amp on the bridge will give you lots of voltage. The main issue is indeed living with the range limitation. Yes this is a bit of “cobble it together” nonsense. You can indeed get a pretty good setup that will give you mili C resolution and tens of mili C accuracy. Best guess is that a single sensor system you can trust will be over $5K. The sensors will be giant RTD probes that are a bit useless for looking at small devices …. sorry about that …. ====== Since this is time nuts …… One can build an R/C oscillator with a thermistor. You can measure the period of the output and get temperature that way. Resolution (obviously) is not going to be hard to get with a Time Nut grade counter. Don’t bother … the jitter is going to get in the way long before you get to 0.01, let alone 0.001C …. Bob > On Sep 26, 2020, at 7:18 AM, Manfred Bartz <[email protected]> wrote: > > A thermistor should do the job. You can buy them in SMD packages and > down to 0.1% accuracy. > How much resolution you get depends on the measurement range and the > ADC you are using. > > A platinum RTD would be another candidate but requires more signal > conditioning. > In 3-wire or 4-wire probe configuration you can compensate for long probe > wires. > > Any sensor you choose should have a thermal mass less that the item > you want to measure. > Generally, a smaller sensor means smaller thermal mass. > > If you really need to resolve 0.01ºC or 0.001ºC then you also need to > pay attention to: > * sensor self-heating > * consider turning off excitation between measurements > * with a thermistor, go with a high R25, i.e. 100kΩ which will help > with keeping self-heating low. > * Temperature coefficient and environment of the thermistor's series resistor. > * Stability of the supply/reference voltage. > > BTW, 0.1% resistors are sensitive to static discharge. A zap can > easily produce a 0.5% change! > > Having really good and stable thermal contact is essential. > The item you are measuring and the sensor should be in an isolated > micro environment. > Airflow or proximity to anything of a different temperature will > potentially cause a temperature gradient between sensor and the > measured item. > > All passive temperature sensors require some sort of linearization, > but that could be done away from the sensor or during post-processing. > For thermistors search for the "Steinhart Hart equation". > > I am not aware of active (smart) sensors with have better than 0.1ºC > resolution, but I also have not done any significant search lately. > > Cheers > -- > Manfred VK3AES > > On Sat, Sep 26, 2020 at 12:46 PM Hal Murray <[email protected]> wrote: >> >> >> I've got a collection of 1-wire gizmos and USB thumb drives. They are great >> for many applications but I'm looking for something better/different. >> >> I'd like something that reads to 0.01 degree or 0.001 degree. I don't need >> accuracy. What I want is reasonable linearity so I can make pretty graphs. >> >> I'd like the actual probe to be small enough so I can poke it inside gear >> like >> a PC and attach it to a crystal. >> >> I'm looking for a USB or serial connection so I can log the data. >> >> Is there an obvious brand/whatever I should be looking at? thermistor? >> thermocouple? ... >> >> I don't care about a display on the device. I don't want a logger, they fill >> up. I want to grab the data on the fly and do my own logging. (But I'm >> happy >> to use a logger if it will do what I want.) >> >> >> -- >> These are my opinions. I hate spam. >> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > > > -- > Manfred VK3AES > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
