[time-nuts] OT, looking for a good science forum

[Bob Camp]

Hi

Yes, indeed you can buy or rent a calibrated RTD. You might be able to rent a quartz thermometer. The HP version (2804) has been history for quite a while. In both cases they come with a cute little disclaimer on the accuracy that more or less says:

"We can't be sure that this stays calibrated through the shipping process, a triple point cell must be used to verify calibration at the use temperature".  

One of the reasons HP dropped the product was that people discovered that need after it had been in production for a quite a while. Hysteresis in the LC cut crystals turned out to be one of several issues that contributed to the problem. 

Pretty much *everything* with a triple point down at 190K is going to have something nasty about it.

Bob

On Jan 26, 2013, at 3:57 PM, "J. Forster" <jfor at quikus.com> wrote:

> You can't be serious. Ammonia gas or liquid is dangerous.
> 
> You can buy calibrated RTDs or rent a quartz thermometer and stay alive.
> 
> YMMV,
> 
> -John
> 
> ===============
> 
> 
>> Hi
>> 
>> If the intent is to come up with a triple point cell to calibrate your
>> thermometer, acetone's triple point (at 178.5K) is a bit low. I still
>> think I'd go with ammonia.
>> 
>> Bob
>> 
>> On Jan 26, 2013, at 2:51 PM, Graham / KE9H <timenut at austin.rr.com> wrote:
>> 
>>> On 1/26/2013 1:29 PM, Paul Amaranth wrote:
>>>>> Message: 4
>>>>> Date: Sat, 26 Jan 2013 16:28:19 +0100
>>>>> From: Fabio Eboli <FabioEb at quipo.it>
>>>>> To: Discussion of precise time and frequency measurement
>>>>> 	<time-nuts at febo.com>
>>>>> Subject: Re: [time-nuts] OT, looking for a good science forum
>>>>> Message-ID: <5ef3f142b075fcab38182666a4e5073b at quipo.it>
>>>>> Content-Type: text/plain; charset=UTF-8; format=flowed
>>>>> 
>>>>> Il 2013-01-26 14:58 Bob Camp ha scritto:
>>>>>> Hi
>>>>>> 
>>>>>> Platinum RTD's are a pretty good bet for -80C, they hold up well down
>>>>>> there. For calibration, ammonia and acetylene both have triple points
>>>>>> in the vicinity. I'd probably try ammonia first, but not for any good
>>>>> Doesn't acetylene have a bad habit of dissociate when pure liquid?
>>>>> 
>>>>> Fabio.
>>>>> 
>>>> Yes, it's normally stored disolved in acetone.  It also spontaneously
>>>> dissociates
>>>> if pressures exceed 15 psig or 30 psi absolute.  That could put a real
>>>> damper on your day.
>>>> 
>>>> 
>>> Just pure acetone works well at dry ice temperatures.  We used crushed
>>> dry ice
>>> in acetone as an alternative when the liquid nitrogen truck was late
>>> making its delivery
>>> for the cryro lab.
>>> 
>>> --- Graham / KE9H
>>> 
>>> ==
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> 
> 
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