Temperature is related to several of my projects: voltage standards, resistance standards, frequency standards, and weather. Air convection is an important part of my projects. I would like to hear more about your experiments, Jan.
Joe Hobart Cool Flagstaff, Arizona On 2/3/2014 2:52 AM, Jan Fredriksson wrote: > Maybe I should not be posting this on the VN list, as it is only indirectly > related to volts. > > Still; I have been getting some messages and feedback, with no disrespect > to me, asking, if I know what I am doing. With no disrespect to the people > who replied, of or on list (on the contrary, I'm grateful for feedback!): > > My background: I have been working for 15 years with thermal engineering > and measurement techniques. I have calibrated in liquid baths, > ovens, against reference probes. I have calibrated reference probes in > water triple cells, and gallium melting pots, (both are ITS-90 temperature > scale reference points) calibrated reference probes etc. I know it its hard > to do measurements with 0.1C accuracy in real life, sometimes even 100C is > very difficult, ie at very high temperatures. Absolute uncertainties at mC > are beyond all but very qualified calibration labs.I also know that > measuring temperature differences in time and space CAN be very accurate, > if conditions are optimal. I frequently measured in stirred water baths > that had a stability of around 0.005Crms overnight (checked with PT100 > reference probes, and actually measured with 0.001 resolution, but with > nothing near the same temperature uncertainty) with thermocouples. > The reference points where huge water-ice slurry Dewars, the thermocouple > measurements where done with Keithley Nanovolt meters and the PT100 where > measured with a reference bridge). > > I am not an electrical engineer, but come from mechanics and thermal > engineering. My PID / control loop maths are now a bit rusty but I have > developed amplifiers for highly capacitive loads before. By searching new > methods and ways, I have also more than once developed practically usable > measurement techniques that people in advance told me where almost > impossible ;-) > > The circuit I am working with, ONLY shows temperature of a sensor, heated > by resistors, taped together, under a shield. I am aware that this is a > serious limitation. Adding any mass to the circuit thermal feedback loop > will be seen as an increased capacitive load to the circuit, so it will of > course be harder to stabilize. Air convection, in and around the final > solution is unpredictable and can dramatically change the heat transfer and > temperature. > > I am mainly thinking of a heater that can keep a small circuit at a > decently stable temperature, by which I mean in the order of 0.1C-0.01C. I > am not really aiming for mC stability in a real life application, it was > something I got, a bit to my surprise, for this circuit which is still on a > breadboard level. But I think that a first board / circuit stable to the > mC level is a decent start and I do think that kind of stability is > possible in a very small scale. > > I think I will not be posting more on this until I have a complete working > solution which may take a month or four... > _______________________________________________ > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
