Hi The Quartz Thermometer died when somebody proved that hysteresis was a big deal on the probes.
Bob On Dec 8, 2013, at 11:22 PM, Tim Shoppa <[email protected]> wrote: > 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 <[email protected]> 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 -- [email protected] >>> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
