[time-nuts] temperature

Azelio Boriani azelio.boriani at screen.it
Mon Dec 9 14:41:03 UTC 2013


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 <dmendesf at 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 <tshoppa at 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 <namichie at 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
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