[time-nuts] temperature sensor

Neville Michie namichie at gmail.com
Wed Jul 23 09:10:44 EDT 2014


To ensure that steam is in a suitable state for temperature measurement
one uses a Hypsometer.
I made one out of tin cans and it sits on an electric hot plate.
It is not rocket science but it really works, my PT100 showed stable temperatures within a 
milliKelvin.
It is made so that the splash is separated from the boiling water and the shielding surfaces 
are maintained at the wet steam temperature. All that is necessary in the design is 
that the pressure drop of the steam is kept below some reasonable number.
The catch is that you must measure the ambient pressure to great precision,
aneroid barometers are hardly good enough except for some specially calibrated devices,
solid state barometric sensors are orders of magnitude too insensitive,
and a mercury barometer (Fortin pattern) requires several calculated corrections 
including the exact value of gravity at the measurement site.

cheers, Neville Michie

On 23/07/2014, at 5:11 AM, Attila Kinali wrote:

> On Tue, 22 Jul 2014 01:17:03 +0100
> Brian D <groups at planet3.freeuk.co.uk> wrote:
> 
>> Saturated steam at standard pressure will be exactly 212F, or 100C.
> 
> Stupid question: How to you ensure that the steam is saturated,
> while keeping a constant pressure?
> 
> I think just buying some indium off ebay and use that as a melting/freezing
> reference is easier than the contraption needed to ensure fully saturated
> steam, with a low temperature gradient over the temperature sensor.
> 
> That said. My investigations into stability of PT100 sensors reveal,
> that the quality ones can be less than 10mK/year, but hysteresis is
> in the same ball park (see [1]).
> 
> 
> 			Attila Kinali
> 
> [1] "Long term stability and hysteresis effects in Pt100 sensors
> used in industry", by Ljungblad, Holmstein, Josefson, Klevedal, 2013
> 
> -- 
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