Is the hysteresis related to the retrace effect? If so, then I think that the quartz thermometer may be succesfully used where the tenperature has only small variations.
On Mon, Dec 9, 2013 at 3:12 PM, Daniel Mendes <dmend...@gmail.com> wrote: > > It´s still used in the oil industry as "the standard" for temp and pressure > monitoring... > > Daniel > > Em 09/12/2013 10:28, Bob Camp escreveu: > >> 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 <tsho...@gmail.com> 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 <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. >> >> _______________________________________________ >> 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.