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열유속
측정센서
SELF-CALIBRATING
HEAT FLUX SENSOR (HFP-01SC-ATX)
HFP-01SC-ATX Self-calibrating heat flux sensor
The HFP-01SC-ATX self-calibrating heat flux
sensortm is a sensor intended for high accuracy measurement of soil
heat flux. Also it offers improved quality assurance of the measurement. The
on-line calibration (the Van den Bos-Hoeksema method) automatically corrects for
various common errors, in particular those due to the non-perfect matching of
the thermal conductivity of sensor and soil, and due to variations of the
thermal conductivity of the soil caused by varying moisture
content.
See also the scientific section on heat flux.
HFP-01SC-ATX can also be used to determine heat transfer
coefficients.
Figure 1 HFP-01SC-ATX
Figure 2 Explanation of the
self-calibrating principle: On the left the normal situation with a heat flux
j. On the right, the film heater
that is mounted on top (1) is activated to generate a well known heat flux
j. The response of the heat flux
sensor is measured. In the ideal situation 50% of the generated flux
j would
pass through the plate (typically 150 W/m2). In case of non matching
thermal conductivities, a deviation (X) will occur. The essence of this approach
is that the flow is divided in an upward flow through undisturbed medium (1+X)
and a downward flow through the heat flux sensor (a disturbance) plus underlying
medium. The (1-X) signal level however, still represents a 0.5 j heat flux level of the normal situation of the picture on the
left.
 
Figure 3 HFP-01SC-ATX dimensions: heater (1) heat flux
sensor body (2),cable (3)
HFP-01SC-ATX is a combination of a heat flux
sensor and a film heater. The primary purpose is to estimate the heat flux
through the surrounding soil. The HFP-01SC-ATX output is a voltage signal that is
proportional heat flux through the sensor. The film heater that is mounted on
top can be activated to perform a calibration (see figure 2), resulting in a new
calibration factor that compensates for the errors made under the circumstances
of that moment. Implicitly also cable connection, data acquisition and data
processing are tested. Also errors due to temperature dependence and instability
of the sensor are eliminated. The result is a much improved accuracy &
quality assurance of the measurement (relative to conventional models such as
model HFP01).
A typical measurement location is equipped
with 2 sensors for good spatial averaging.
The product manual can be obtained via
e-mail. A program for the Campbell Scientific CR10X is available.
SUGGESTED
USE
Scientific grade measurement of soil heat
flux.
HEAT FLUX
SENSOR SPECIFICATIONS
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Sensitivity (nominal): 50 µV/ Wm2
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Resistance
(nominal): 2 W
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Temperature range: -30 to +70
°C
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Expected accuracy: ± 3%
FILM
HEATER SPECIFICATIONS
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Resistance
(nominal): 100 W
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Voltage
input/output: 9-15 VDC/ 0-2VDC
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Duration of calibration: ± 3
min at 1.5 Watt
typically
every 3 or 6 hours
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Average power
consumption: 0.02 to 0.04 Watt
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