User manual

Hukseflux Thermal Sensors
HFP01SC Manual v0811 page 10/33
1.2 Theory on heat flux measurement errors
Using a normal heat flux sensor, there are several common error
sources. In soil these are in particular the deflection error and
the temperatre dependence. In case of use of HFP01SC, typically
in the soil, the resistance error is neglected.
As a first approximation, the heat flux is expressed as:
ϕ = V
sen
/ E
sen
1.2.1
When mounting the sensor in or on an object with limited
thermal resistance, the sensor thermal resistance itself might be
significantly influencing the undisturbed heat flux. One part of
the resulting error is called the resistance error, reflecting a
change of the total thermal resistance of the object.
Figure 1.2.1 The resistance error: a heat flux sensor (2)
increases or decreases the total thermal resistance of the object
on which it is mounted (1) or in which it is incorporated. This can
lead either to a larger of smaller (increase of or decrease of
the- ) heat flux (3).