[time-nuts] temperature

[Daniel Mendes]

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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