HFP01SC Self-calibrating heat flux sensor
The HFP01SC 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.
HFP01SC can also be used to determine heat transfer coefficients. See HFP01SC
Info Note.
Free: For a nice clear print of the original product
brochure (PDF) click here.
Figure 1 HFP01SC
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 HFP01SC dimensions: heater (1) heat flux sensor body (2),cable (3)
HFP01SC 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 HFP01SC 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
-
Sensitivity
(nominal): 50 µV/ Wm2
-
Resistance
(nominal): 2 W
-
Temperature
range: -30 to +70 °C
-
Expected
accuracy: ± 3%
FILM HEATER SPECIFICATIONS
-
Resistance
(nominal): 100 W
-
Voltage
input/output: 9-15 VDC/ 0-2VDC
-
Duration
of calibration: ± 3 min at 1.5 Watt
typically every 3 or 6 hours
-
Average
power consumption: 0.02 to 0.04 Watt
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