Hukseflux HTR02 Series User manual
HTR02 series manual v2203 2/26
Warning statements
Cautionary statements are subdivided into four categories: danger, warning, caution and
notice according to the severity of the risk.
DANGER
Failure to comply with a danger statement will lead to death or serious
physical injuries.
WARNING
Failure to comply with a warning statement may lead to risk of death or
serious physical injuries.
CAUTION
Failure to comply with a caution statement may lead to risk of minor or
moderate physical injuries.
NOTICE
Failure to comply with a notice may lead to damage to equipment or may
compromise reliable operation of the instrument.
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Contents
Warning statements 2
Contents 3
List of symbols 4
Introduction 5
1Ordering and checking at delivery 7
1.1 Ordering HTR02 7
1.2 Included items 7
1.3 Quick instrument check 8
2Instrument principle and theory 9
2.1 Basic operation 9
2.2 A self-test for heat flux sensors 9
2.3 Using heaters with FHF05 series 10
2.4 Calibrating heat flux sensors 12
2.5 An in-situ test for heat flux sensors 13
3Specifications of HTR02 series 16
3.1 Specifications of HTR02 series 16
3.2 Dimensions of HTR02 series 18
4Installation of HTR02 series 19
4.1 Site selection and installation 19
4.2 Electrical connection 21
5Maintenance and trouble shooting 23
5.1 Recommended maintenance and quality assurance 23
5.2 Trouble shooting 24
5.3 Calibration and checks in the field 24
6Appendices 25
6.1 EU declaration of conformity 25
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List of symbols
Quantities Symbol Unit
Heat flux ΦW/m²
Voltage U V
Sensitivity S V/(W/m2)
Temperature T °C
Thermal resistance per unit area Rthermal,A K/(W/m²)
Area A m2
Electrical resistance R Ω
Electrical power P W
Subscripts
Property of heatsink heatsink
Property of heater heater
Property of sensor sensor
Maximum value, specification limit maximum
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Introduction
HTR02 series are heaters that can be used for calibration and functionality checks of FHF-
type heat flux sensors like FHF05 series. The heaters have a 4-wire connection with a
known surface area and electrical resistance. Users can now easily and objectively check
their sensor performance before and after use. HTR02 series is available in two different
models: 50 x 50 and 85 x 85 mm. See also FHF05SC series heat flux sensor with
integrated heater.
Measuring heat flux, users may wish to regularly check their sensor performance. A quick
check or a formal calibration is now possible with HTR02 series plus some accessories
that most laboratories will have in-house. The HTR02 series heaters have a well
characterised traceable surface area and electrical resistance.
In a typical test setup, the heat losses through the insulation are typically smaller than 3
% and may be ignored. Measuring the heater power (voltage Uheater squared divided by
resistance Rheater), and dividing by the surface area Aheater, gives the applied heat flux.
The heat flux sensor sensitivity S is the voltage output Usensor divided by the applied heat
flux.
S = (Usensor∙Rheater∙Aheater)/Uheater² (Formula 0.1)
The reproducibility of this test is much improved when using contact material between
heater, sensor and heat sink.
HTR02 series has unique features and benefits:
•makes it possible to perform a simple test
•guarantees sensor stability
•matches FHF05 series heat flux sensors
Figure 0.1 On the left model HTR02-85X85 heater for calibration and verification of
performance of the models of FHF05 series heat flux sensors, on the right model FHF05-
85X85 to which HTR02-85X85 may be applied. See also figure 3.2.1 for dimensions.
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HTR02 series is a foil heater and comes in two models. Either it can be used in
combination with foil heat flux sensors such as FHF05 series for test and calibration
purposes, or it can be used as a general-purpose heater.
Options:
•available with standard cable length -02 metre, or change -02 to -05 or -10 metres
for the respective cable length
•cables can also be ordered separately in 2, 5 or 10 metres length
See also:
•FHF05SC heat flux sensor with integrated heater
•FHF05 series general purpose heat flux sensor
•view our complete range of heat flux sensors
HTR02 series manual v2203 7/26
1Ordering and checking at delivery
1.1 Ordering HTR02
The standard configuration of HTR02 series is model 50X50 with 2 metres of cable, order
code: HTR02-50X50-02.
Common options are:
•model HTR02-85X85
•-05 or -10 metres cable length
•with a separate cable in 2, 5 or 10 metres cable length
1.2 Included items
Arriving at the customer, the delivery should include:
•HTR02 heater with cable of the length as ordered
•product certificate matching the instrument serial number
Figure 1.2.1 Model HTR02-50X50 with serial number and resistance shown at the end of
the cable.
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1.3 Quick instrument check
A quick test of the instrument can be done by connecting it to a multimeter:
1. Check the heater serial number on the label at the end of HTR02’s cable against the
product certificate provided with the heater.
2. Inspect the instrument for any damage.
3. Check the electrical resistance of the heater between any of the yellow wires and any
of the grey wires. Use a multimeter at the 1 kΩ range. Typical resistance should be
around 120 Ω for model -50X50 and around 40 Ω for model -85X85. Infinite
resistance indicates a broken circuit; zero or a lower than 1 Ω resistance indicates a
short circuit.
4. Check the electrical resistance between the 2 yellow wires. These resistances should
be in the 0.1 Ω/m range, so 0.2 Ω in case of the standard 2 m wire length. Higher
resistances indicate a broken circuit. Repeat this measurement for the 3 grey wires.
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2Instrument principle and theory
HTR02 series is a foil heater. Either it can be used in combination with foil heat flux
sensors such as FHF05 series for test and calibration purposes, or it can be used as a
general-purpose heater.
2.1 Basic operation
If a voltage Uheater is applied to the heater such that an electrical current Iheater runs
through the heater, the heater power Pheater may be calculated as:
Pheater = Uheater∙Iheater = Uheater2/Rheater = Iheater2∙Rheater
where Rheater is the heater electrical resistance. If the heater is placed in a uniform
environment (i.e., same medium on both sides of the heater) the applied heat flux Φ in
either direction may be calculated as:
Φ = Pheater/(2·Aheater) (Formula 2.1.1)
where Aheater is the heater area. If, however, the heater is placed in between a thermal
insulator and a good thermal conductor the heat flux Φ in the direction of the conductor
is:
Φ = Pheater/Aheater (Formula 2.1.2)
Other cases exist as well. Users need to evaluate which case applies to their situation.
2.2 A self-test for heat flux sensors
In combination with a heat flux sensor such as FHF05 series, HTR02 can be used to test
the response of the heat flux sensor. To this end HTR02 should be positioned directly on
top of the heat flux sensor such that HTR02 can be used to apply a heat flux through the
heat flux sensor.
A self-test is started by switching on HTR02, while recording the heat flux sensor output
signal and the HTR02 heater power and finalised by switching HTR02 off. During the
heating interval, Iheater is fed through the foil heater which generates a heat flux
proportional to the heater power. Pheater can be measured in several different ways:
•heater voltage and current, Pheater = Uheater∙Iheater (Formula 2.2.1)
•heater voltage and known heater resistance, Pheater = Uheater2/Rheater (Formula 2.2.2)
•heater current and known heater resistance, Pheater = Iheater2∙Rheater (Formula 2.2.3)
If performed in a four-wire configuration the first method is preferred because it is
generally more accurate than the latter two methods, however it requires both a
voltmeter and an ammeter instead of just one of the two.
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Analysis of the heat flux sensor response to the heating (the self-test) serves several
purposes:
•first, the amplitude and response time under comparable conditions are indicators of
the sensor stability. See 2.5 for application examples.
•second, the functionality of the complete measuring system is verified. For example:
a broken cable is immediately detected.
•third, under the right conditions, after taking the sensor out of its normal
environment, the self-test may be used as calibration. See 2.4 for more details.
Compatible compatible
2.3 Using heaters with FHF05 series
HTR02 series is compatible with the models from the FHF05 series. Model FHF05-50X50
and -85X85 fit directly with HTR02-50X50 and -85X85 respectively.
Models FHF05-10X10 and FHF05-15X30 fit with HTR02-50X50. Model FHF05-15X85 can
be used with HTR02-85X85. Because in these cases the heater is larger than the sensor,
it is recommended to make a guard when using these models with HTR02. See table
2.3.1 for an overview of the models and suggested heaters.
Figure 2.3.1 Using heater model HTR02-50X50 with heat flux sensor FHF05-15X30.
A plastic guard is made with help of a 3D-printer.
To get a representative measurement, the heater should ‘see’ the same environment.
Surrounded by a material like a metal heat sink, the sensor will locally increase the
thermal resistance. The heat from the heater will follow the easiest path; in the case the
heater is larger than the sensor, flow to the metal heat sink. Therefore, the sensor will
measure an underestimation of the actual heat flux.
HTR02 series manual v2203 11/26
Figure 2.3.2 Using HTR02 series heaters with FHF05 series. FHF05 models -10X10 ans -
15X30 are compatible with HTR02-50X50. Model FHF05-15X85 is compatible with HTR02-
85X85. We recommend making a guard around the sensor with equal thermal resistance
and thickness. The orange-coloured part is the area where we recommend making a
guard.
To create an environment with constant thermal resistance, make a guard around the
sensor with equal thermal resistance and thickness. FHF05 series have a thermal
resistance of Rthermal = 11 × 10-4 K/(W/m²) and a thickness of 0.4 × 10-3 m.
We recommend a guard made from plastic. Most plastics have a thermal resistance in the
same order of magnitude as the base material of the sensor. Use tape of comparable
thickness or print a guard with a 3D printer. See figure 2.3.1.
Table 2.3.1 Suggested use of FHF05 series with HTR02 series.
MODEL FHF05
SUGGESTED HTR02 MODEL
GUARD RECOMMENDED?
FHF05-10X10
HTR02-50X50
yes
FHF05-15X30
HTR02-50X50
yes
FHF05-50X50
HTR02-50X50
no
FHF05-15X85
HTR02-85X85
yes
FHF05-85X85
HTR02-85X85
no
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2.4 Calibrating heat flux sensors
It is recommended to recalibrate heat flux sensors at least once every two years. HTR02
series can be used to calibrate heat flux sensors such as the models in the FHF05 series.
In a typical calibration setup as shown in figure 2.4.1, a stack is made of a heatsink, the
heat flux sensor to be calibrated, the heater and an insulating material. In such a setup,
the heat losses through the insulation is for FHF-type sensors in the order of magnitude
of 3 %. In this case heat generated by HTR02 flows through the heat flux sensor to the
heat sink. Measuring the heater power Pheater, and dividing by the surface area Aheater,
gives the applied heat flux:
Φ = Pheater/Aheater (Formula 2.3.1)
The heat flux sensor sensitivity Sis the voltage output of the sensor Usensor divided by the
applied heat flux Φ:
S = Usensor/Φ (Formula 2.3.2)
The reproducibility of this test is much improved when using contact material (such as
glycerol or a thermal paste) between heater, sensor and heat sink.
Figure 2.4.1 Calibration of a heat flux sensor; a typical stack used for calibration
consists of a block of metal (mass > 1 kg), for example aluminium (5), the heat flux
sensor (3), HTR02 (2) and an insulation foam (1). Under these conditions, heat losses
through the insulation are negligible. Heat flux (4) flows from hot to cold.
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2.5 An in-situ test for heat flux sensors
The HTR02 series heater can be used to test the stable performance of the heat flux
sensors such as FHF05 series.
HTR02 series should be installed on top of the heat flux sensor, preferably on the side of
the heat flux sensors with the more insulating medium. In case the heater is used for
repeated verifications at one location, consider using our FHF05SC series: sensor with a
HTR02 heater integrated.
A typical stability check is performed based on the step response of the measured heat
flux and sensor temperature to a heat flux applied by HTR02. Upon installing the heat
flux sensor and HTR02, a reference measurement should be made. A time trace of the
heater power, the measured heat flux and the measured sensor temperature should be
stored as reference data. Stable operation of the heat flux sensor can then be confirmed
at any time by comparing to the reference measurement. The test protocol consists of
the following steps:
1. Make sure that the absolute temperature is similar to that during the reference
measurement.
2. Check the heater resistance stability. This can be done accurately by using the four
heater wires to conduct a four-point resistance measurement.
3. Record a time trace of the heater power, the measured heat flux and the sensor
temperature; the same parameters as in the reference data. Normalise the data by
the heater power. Under normal circumstances (if the heater is stable) this process
scales with Uheater2.
4. Compare patterns of heat flux and temperature rise and fall. In both cases relative to
the values just before heating.
•When the signal patterns match, amplitude differences, after correction for heater
power, point towards sensor instability. In this case recalibration of the sensor
may be required (Figure 2.5.1).
•Non-matching patterns point towards changes in sensor environment. This can for
example be the result of a loss of thermal contact between sensor and object
(Figure 2.5.2) or the presence of convective heat losses (Figure 2.5.3).
HTR02 series manual v2203 14/26
Figure 2.5.1 In-situ sensor stability check. Comparison of responses to stepwise heating
relative to reference curves. Normalised to heater power (P) and relative to the heat flux
and the temperature just before heating. Solid graphs show heat flux, dotted graphs show
temperature. The black HF and T signals are the reference curves at installation. The
sensor shows non-stability, loses sensitivity over time, which results in the red responses:
equal response times, lower heat flux and equal temperature rise.
Figure 2.5.2 In-situ sensor stability check. Comparison of responses to stepwise heating
relative to reference curves. Normalised to heater power (P) and relative to the heat flux
and the temperature just before heating. Solid graphs show heat flux, dotted graphs show
temperature. The black HF and T signals are the reference curves at good thermal contact.
The sensor loses thermal contact, which results in the blue responses: slower response
times, lower heat flux and higher temperature rise.
HTR02 series manual v2203 15/26
Figure 2.5.3 In-situ sensor stability check. Comparison of responses to stepwise heating
relative to reference curves. Normalised to heater power (P) and relative to the heat flux
and the temperature just before heating. Solid graphs show heat flux, dotted graphs
show temperature. The black HF and T signals are the reference curves at zero wind
speed. The sensor is exposed to convection, which results in the grey responses: faster
response times at lower heat flux and lower temperature rise.
HTR02 series manual v2203 16/26
3Specifications of HTR02 series
3.1 Specifications of HTR02 series
HTR02 series is a heater with 4-wire connection with a known surface area and electrical
resistance. It is designed for calibration and functionality checks of FHF-type sensors but
can also be used for general heating purposes.
Table 3.1 Specifications of HTR02 series (continued next page).
HTR02 SERIES SPECIFICATIONS
Product type
foil heater
Measurement function / required
programming
depends on the application
Required readout
1 x current channel and 1 x voltage channel,
alternatively 1 x current channel or alternatively 1
voltage channel.
currents may be measured using a voltage channel
which acts as a current measurement channel using a
current sensing resistor
heater: 1 x switchable 12 VDC
Rated load on the cable
≤1.6 kg
Rated bending radius
≥ 7.5 x 10-3 m
Operating temperature range
-40 to +150 °C
Heater length and width per dimension
HTR02-50X50
(48 x 47.6) x 10-3 m
HTR02-85X85
(83 x 82.6) x 10-3 m
Heater area
HTR02-50X50
2381 x 10-6 m2
HTR02-85X85
7022 x 10-6 m2
Passive guard area
HTR02-50X50
2152 x 10-4 m2
HTR02-85X85
3692 x 10-4 m2
Guard width to thickness ratio
HTR02-50X50
6 m/m
HTR02-85X85
6 m/m
Heater thickness
0.1 x 10-3 m
Heater thermal resistance
4 x 10-4 K/(W/m2)
Heater thermal conductivity
0.27 W/(m·K)
Standard cable length
2 m
Heater wiring
4 x copper wire, AWG 28, solid core, bundled with PFA
sheath
Wire diameter
1 x 10-3 m
Marking
1 x label at the end of HTR02’s cable, showing serial
number and nominal resistance
IP protection class
IP67
Rated operating relative humidity range
0 to 100 %
Gross weight including 2 m wires
approx. 0.5 kg
Net weight including 2 m wires
approx. 0.5 kg
ELECTRICAL CHARACTERISTICS
Heater resistance (nominal) per dimension (measured value supplied with each sensor in the
production report)
HTR02-50X50
120 Ω ± 10 %
HTR02-85X85
40 Ω ± 10 %
Temperature coefficient of resistance
< 0.02 %/°C
Heater rated power supply
24 VDC
HTR02 series manual v2203 17/26
Heater power supply
12 VDC (nominal)
Power consumption at 12 VDC per dimension
HTR02-50X50
1.20 W
HTR02-85X85
3.60 W
Nominal heat flux at 12 VDC per dimension
HTR02-50X50
500 W/m²
HTR02-85X85
500 W/m²
INSTALLATION AND USE
Recommended number of heaters
one per sensor per measurement location
Installation
see recommendations in this user manual
Wire extension
see chapter on cable extension or order heaters with
longer cables
HTR02 series manual v2203 18/26
3.2 Dimensions of HTR02 series
Figure 3.2.1 Models HTR02 -50X50 and -85X85; Y1 = 47.6 or 82.6 and Y2=48 or 83,
dimensions in x 10-3 m
(1) heater area
(2) passive guard
(3) connection block for strain relief
(4) cable, standard length C = 2 m
HTR02 series manual v2203 19/26
4Installation of HTR02 series
4.1 Site selection and installation
Table 4.1.1 Recommendations for installation of HTR02 series.
Surface cleaning and
levelling
create a clean and smooth surface of at least the same outer dimensions
of the heater: (50 x 50) or (85 x 85) x 10-3 m
Mounting: avoiding
strain on the heater-
to-cable transition
the heater-to-cable transition is vulnerable
during installation as well as operation, the user should provide proper
strain relief of the cable so that the transition is not exposed to significant
force
first install the cable including strain relief and after that install the heater
Mounting: using a
guard
In case the sensor is smaller than the HTR02 heater, a guard is
recommended. We suggest making a guard of a material with equal
thermal resistance and thickness for best measurement results. See
section 2.3.
Mounting:
curved surfaces
when mounting HTR02 on curved surfaces, observe the rated bending
radius
Mounting:
combination with heat
flux sensor
when mounting the HTR02 in combination with a heat flux sensor such as
the FHF05, keep the directional sensitivity of the heat flux sensor and the
position of the heater in mind
Short term
installation
avoid any air gaps between heater and surface. Air thermal conductivity
is in the 0.02 W/(m·K) range, while a common glue has a thermal
conductivity around 0.2 W/(m·K). A 0.1 x 10-3 m air gap increases the
effective thermal resistance of the sensor by 200 %
to avoid air gaps, we recommend thermal paste or glycerol for short term
installation
use tape to fixate the connection block of the heater
usually, the cables are provided with an additional strain relief, for
example using a cable tie mount as in Figure 4.1.1
Permanent
installation
for long-term installation, fill up the space between heater and object
with silicone construction sealant, silicone glue or silicone adhesive, that
can be bought in construction depots.
we discourage the use of thermal paste for permanent installation
because it tends to dry out. Silicone glue is more stable and reliable
HTR02 series manual v2203 20/26
Figure 4.1.1 Installation of model HTR02-50X50 using tape to fixate the sensor and the
connection block. Extra strain relief of the cable is provided using cable tie mounts
equipped with double-sided tape as adhesive. As indicated in Table 4.1.1, tapes fixating
the sensor are preferably taped over the passive guard area. In this case, a third tape (in
the middle) is added for extra support.
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