Am 23.07.2013 19:09, schrieb Jan Sennesael:
> I am mesuring on a copper tube (sensor attached with tie wraps so the flat
> side makes a good connection).
> The temps i am measuring are between 12 and 22 °C.
>
This is problematic because it's near to the ambient temperature. With
such a low temperature difference, the heat transferred between tube and
sensor is very small, so you cannot neglect the amount of heat
transferred between sensor and ambient.
My guess is the difference in the measurements of the two sensors is
coming from different heat conduction at the sensor/tube border. The
arrangement is that way I guess:
Tube
---------------------------
Heat Conductive Paste
---------------------------
Sensor casing
---------------------------
Sensor
---------------------------
Sensor casing
---------------------------
Ambient
So you measure *both* the temperature of the tube and the ambient.
I suggest you to replace the plastic tie-wraps by a copper clamp so the
whole sensor is nearly enclosed in metal - all at the same temperature
as the tube. That way it wouldn't measure the ambient temperature even
if the heat conduction between sensor and tube isn't excellent.
Parasite power is a no-go at such low temperatures as it adds another
non-neglectable heat source inside the sensor which complicates things
even more.
Kind regards
Jan
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