You also must take into account the wiring. The wires go to the sensor, up
to the die itself, and are made of good heat conducting material. Use as
narrow wire as possible, and stuff a reasonable amount of the wire under
the insulation. I mean the wire not just comes in a plain line, but is
wrapped to a zig-zag a few times, so outside heat has to be conducted over
20-30cm to reach the sensor.
Vajk
On Tue, Jul 23, 2013 at 9:33 PM, Jan Kandziora <[email protected]> wrote:
> 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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