Interestingly, HP for a long time sold"quartz thermometers" based around a probe with a quartz crystal with a well characterized linear temperature coefficient. They called the crystal cut "LC" (Linear Coefficient):
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1965-03.pdf http://en.wikipedia.org/wiki/Quartz_thermometer On Sun, Dec 8, 2013 at 10:55 PM, Neville Michie <namic...@gmail.com> wrote: > Hi, > I use a HP3468A multimeter to measure a PT100 platinum resistance > thermometer. It gives me resolution of one mK, but calibration is another > matter. > It is best to use a 4 terminal device, but 2 terminal into the 4 terminal > input works well. Thermoelectric effects and the requirement for 1 > microvolt stability > makes wiring them into your own circuit difficult. One of the great > technical difficulties is to get a resistor to compare them against, it > must be very stable, > have no thermoelectric effects and have a temperature coefficient in the > order of one PPM. I always admire the way HP designed their ohm meters. > There are other issues, however. Whereas a volt meter can connect > perfectly to a reference, a PRT can only report its own temperature. > That is no problem when you are working in a well stirred water bath, that > will have the PRT at the same temperature as the object in the same bath. > When you get to measure air temperature you are into serious sampling > errors, the PRT has some self heating and so is air velocity sensitive, and > the air > you are measuring may not be the same air as is over your OCXO or item of > interest. There is a personal plume of warm air rising from an observer, so > you must be careful with your measurement technique. > The same problems occur with quartz crystal thermometers, which is why > they are not more commonly found in surplus. > A PT100 sensor is quite cheap, and their calibration is little short of > brilliant. However a they would cost much more if their calibration is > traceable. > For my use, I use an ice-point cell as a calibration check, with care you > get 10mK accuracy. You only need the knowledge how to set it up, a blender > to make ice slush, > and a picnic vacuum flask, to make your own calibration reference. > I use thermistors for air measurement, and calibrate them against the > PT100 in a thermostatic water bath. Thermistors can be run with a very low > level of self heating and they are very sensitive, their resistance > changes 4% per Centigrade degree, and they come in high values like 100K > ohm. You read > them in a bridge circuit with a voltmeter, so they are many orders of > magnitude easier to use than a 100 ohm PRT. > They are made small enough to get them in close contact > with the object to be measured. > If you want to know about humidity measurement I can tell you much about > that, > cheers, > Neville Michie > > On 08/12/2013, at 12:40 PM, Mark Spencer wrote: > > > Sorry if this is somewhat off topic, but I'd be interested in more > details re precision temperature measurement devices. Have been using an > inexpensive USB temperature sensor for the last year or so to monitor the > temperature in my lab and have been looking at the correlation between > frequency shifts in some ocxo's vs temperature changes. I should also > start taking humidity measurements as well at some point. > > > > > > Any pointers re suitable instruments to accomplish this that can be > sourced via the usual surplus sources would be welcome. > > > > Thanks in advance > > Mark Spencer > > > > Sent from my iPad > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.