[time-nuts] Any experienced HP 2804A thermometer users out there?

John Ackermann N8UR jra at febo.com
Sat Jan 24 12:15:21 EST 2009


The immersion depth does make a difference in ultimate accuracy, but 
20cm is not required.  Per the manual, for the probe I have available, 
the "immersion error" is 0.001 degree C at 9cm, and 0.01C for 3.5cm 
insertion.  Of course, both are impractical for a surface measurement.

This is clearly a case of picking the right tool for the job!

John
----

Henk Termeer said the following on 01/24/2009 11:58 AM:
> Hello John,
> 
> I have been searching for pictures and found this
> http://www.harlanlabs.com/2804a.jpg if you have a probe like this, no grease
> will help you.
> The quartz cristal is some where in the bulp on the end of the probe and is
> not in direct contact, just like a cristal for a osicillator (because it has
> to be able to move), so the thermal resistance between the bulp and the
> cristal is high. If you make contact to a pc board, you will measure
> something between the enviroment temperature and the board temperature, but
> you will never know what you measure most.
> This probe is excelent for calibration in liquits or gas but you have to
> insert it at least 20 cm.
> 
> Best regards,
> 
> Henk
> 
> On Sat, Jan 24, 2009 at 5:39 PM, John Ackermann N8UR <jra at febo.com> wrote:
> 
>> The best I can get. This is time-nuts, after all.  :-)
>>
>> I'm certainly not looking for the full millidegree accuracy of the
>> thermometer, but have always been curious about heat transfer issues
>> with thermometer probes and wondered if there were any tricks apart from
>> laying the end of the probe horizontally on the board (maybe with the
>> help of some thermal grease, as Brooke suggested).  The challenge is the
>> relatively small contact area between the circular probe and the flat
>> board, and the corresponding fact that the majority of the probe's
>> surface area is in contact with the ambient air rather than the surface
>> of interest.
>>
>> John
>> ----
>>
>> Mike Feher said the following on 01/24/2009 11:15 AM:
>>> What type of accuracy are you looking for John?
>>>
>>>
>>>
>>> Mike B. Feher, N4FS
>>> 89 Arnold Blvd.
>>> Howell, NJ, 07731
>>> 732-886-5960
>>>
>>>
>>> -----Original Message-----
>>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>>> Behalf Of John Ackermann N8UR
>>> Sent: Saturday, January 24, 2009 10:42 AM
>>> To: Discussion of precise time and frequency measurement
>>> Subject: [time-nuts] Any experienced HP 2804A thermometer users out
>> there?
>>> The temperature probes for the 2804A quartz thermometer seem primarily
>>> intended for liquid immersion.  I'm looking for practical tips on how to
>>> couple the probe to a solid surface (e.g., a PC board) for accurate
>>> temperature measurements of the surface.
>>>
>>> Anyone know the best way to do this?
>>>
>>> Thanks,
>>>
>>> John
>>>
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> 
> 
> 




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