Hukseflux FHF05 Series User manual

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USER MANUAL
FHF05 series
Foil heat flux sensors with thermal spreaders, flexible,
5 different dimensions and sensitivities, with temperature
sensor

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Cautionary 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
Cautionary statements 2
Contents 3
List of symbols 4
Introduction 5
1Ordering and checking at delivery 8
1.1 Ordering FHF05 8
1.2 Included items 8
1.3 Quick instrument check 9
2Instrument principle and theory 11
3Specifications of FHF05 series 14
3.1 Specifications of FHF05 series 14
3.2 Dimensions of FHF05 series 18
4Standards and recommended practices for use 20
4.1 Heat flux measurement in industry 20
5Installation of FHF05 series 21
5.1 Site selection and installation 21
5.2 Installation on curved surfaces 23
5.3 Electrical connection 24
5.4Requirements for data acquisition / amplification 27
6Maintenance and trouble shooting 28
6.1 Recommended maintenance and quality assurance 28
6.2 Trouble shooting 29
6.3 Calibration and checks in the field 30
7Appendices 32
7.1 Appendix on cable and wire extension 32
7.2 Appendix on installation of FHF05 sensor foil 33
7.3 Appendix on using FHF05 series with BLK –GLD sticker series 36
7.4 Appendix on standards for calibration 37
7.5 Appendix on calibration hierarchy 38
7.6 Appendix on correction for temperature dependence 38
7.7 Appendix on measurement range for different temperatures 39
7.8 Appendix on temperature measurement accuracy 40
7.9 EU declaration of conformity 42

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List of symbols
Quantities Symbol Unit
Heat flux ΦW/m²
Voltage output U V
Sensitivity S V/(W/m2)
Temperature T °C
Thermal resistance per unit area Rthermal,A K/(W/m²)
subscripts
property of heatsink heatsink
maximum value, specification limit maximum

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Introduction
FHF05 series are the latest standard model for general-purpose heat flux measurement.
Models are available in five dimensions and sensitivities. Significantly thinner and more
flexible, FHF05 series replaces earlier models FHF01 to FHF04. All FHF05 models are very
versatile: they have an integrated temperature sensor and thermal spreaders to reduce
thermal conductivity dependence. It is applicable over a temperature range from –70 to
+120 °C. FHF05 series measures heat flux from conduction, radiation and convection.
Optionally, black BLK and gold GLD stickers are available for every sensor model to
separately determine heat transport by radiation and convection.
All FHF05’s measure heat flux through the object in which it is incorporated or on which it
is mounted, in W/m2. The sensor in FHF05 is a thermopile. This thermopile measures the
temperature difference across FHF05’s flexible body. A type T thermocouple is integrated
as well. The thermopile and thermocouple are passive sensors; they do not require
power.
Multiple small thermal spreaders, which form a conductive layer covering the sensor,
help reduce the thermal conductivity dependence of the measurement. With its
incorporated spreaders, the sensitivity of FHF05 is independent of its environment. Many
competing sensors do not have thermal spreaders. The passive guard area around the
sensor reduces measurement errors due to edge effects and is also used for mounting.
Figure 0.1 Model FHF05-50X50 foil heat flux sensor with thermal spreaders: thin, flexible
and versatile
Using FHF05 series is easy. It can be connected directly to commonly used data logging
systems. The heat flux in W/m2is calculated by dividing the FHF05 output, a small voltage,
by the sensitivity. The sensitivity is provided with FHF05 on its product certificate.
All FHF05’s have unique features and benefits:

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•flexible (bending radius ≥ 7.5 x 10-3 m)
•low thermal resistance
•wide temperature range
•fast response time
•large guard area
•integrated thermal spreaders for low thermal conductivity dependence
•integrated type T thermocouple
•robustness, including cable and connection block which may be used as strain relief
between sensor and cable
•IP protection class: IP67 (essential for outdoor application)
Equipped with a protective potted connection block, which may serve as strain relief so
that moisture does not penetrate, FHF05 has proven to be very robust and stable.
Figure 0.2 Model FHF05-15X85 foil heat flux sensor being installed to measure heat flux
on a pipe
FHF05 has calibration that is traceable to international standards. The factory calibration
method follows the recommended practice of ASTM C1130 - 21. When used under
conditions that differ from the calibration reference conditions, the sensitivity of the
FHF05 series to heat flux may be different than stated on its certificate. See Chapter 2 in
this manual for best practices.
Would you like to study energy transport / heat flux in detail? Hukseflux helps taking this
measurement to the next level: order FHF05 series with radiation-absorbing black BLK and
radiation-reflecting gold GLD stickers. You can then measure convective + radiative flux
with one, and convective flux only with the other. Subtract the two measurements and you
have radiative flux. They can be applied to the sensor by the user or ordered pre-applied
at the factory; see the BLK –GLD sticker series user manual and installation video for
instructions. Stickers are avaible for every sensor model.

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Figure 0.3 Model FHF05-50X50 heat flux sensor: with BLK-50X50 and GLD-50X50
stickers
See also:
•FHF05SC series for a self-calibrating version of FHF05
•heater HTR02 series, for calibration and verification of performance of FHF-type
sensors
•model HFP01 for increased sensitivity (also consider putting two or more FHF05’s in
series)
•BLK - GLD sticker series for every sensor dimension to separate radiative and
convective heat fluxes
•Hukseflux offers a complete range of heat flux sensors with the highest quality for
any budget

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1Ordering and checking at delivery
1.1 Ordering FHF05
The standard configuration of FHF05 series is FHF05-50X05-02, model 50X50 with 2
metres of cable. Common options are:
•model FHF05-10X10
•model FHF05-15X30
•model FHF05-15X85
•model FHF05-85X85
•change -02 to -05 or -10 metres for the respective cable length
•without wiring, without connection block
•with a separate cable in 2, 5, or 10 metres cable length
•with LI19 hand-held read-out unit / datalogger; NOTE: LI19 measures heat flux only,
not temperature
•with HTR02 series, a foil heater of calibration and verification of performance
•BLK black sticker (to measure radiative as well as convective heat flux)
•GLD gold sticker (to measure convective heat flux only)
•BLK - GLD sticker series can also be ordered pre-applied at the factory for every
sensor dimension
1.2 Included items
Arriving at the customer, the delivery should include:
•heat flux sensor FHF05 with wires of the length as ordered
•product certificate matching the instrument serial number

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Figure 1.2.1 Model FHF05-50X50 with serial number and sensitivity shown at the end of
the cable
1.3 Quick instrument check
A quick test of the instrument can be done by connecting it to a multimeter.
1. Check the sensor serial number and sensitivity on the label at the end of FHF05’s cable
against the product certificate provided with the sensor.
2. Inspect the instrument for any damage.
3. Check the electrical resistance of the sensor between the red [+] and black [-] wires.
Use a multimeter at the 1k Ω range. Measure the sensor resistance first with one
polarity, then reverse the polarity. Take the average value. The typical resistance of the
wiring is 0.3 Ω/m. Typical resistance should be the nominal sensor resistance mentioned
in table 3.1.1 plus 0.6 Ω for the total resistance of two wires for each metre (back and
forth). Infinite resistance indicates a broken circuit; zero or a lower than 1 Ω resistance
indicates a short circuit.
4. Check the electrical resistance of the thermocouple between the brown [+] and white
[-] wires. Use a multimeter at the 100 Ω range. Measure the thermocouple resistance
first with one polarity, then reverse the polarity. Take the average value. The typical
resistance of the copper wiring is 0.3 Ω/m, for the constantan wiring this is 6.5 Ω/m.
Typical resistance should be the nominal thermocouple resistance of 2.5 Ω plus 6.8 Ωfor
the total resistance of the two wires of each metre (back and forth). Infinite resistance
indicates a broken circuit; zero or a lower than 1 Ω resistance indicates a short circuit.

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5. Check if the sensor reacts to heat: put the multimeter at its most sensitive range of
DC voltage measurement, typically the 100 x 10-3 VDC range or lower. Expose the sensor
to heat. Exposing the back side (the side without the dot) to heat should generate a
positive signal between the red [+] and black [-] wires. Doing the same at the front side
(the side with the dot), reverses the sign of the output.

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2Instrument principle and theory
FHF05’s scientific name is heat flux sensor. A heat flux sensor measures the heat flux
density through the sensor itself. This quantity, expressed in W/m2, is usually called
“heat flux”.
FHF05 users typically assume that the measured heat flux is representative of the
undisturbed heat flux at the location of the sensor. Users may also apply corrections
based on scientific judgement.
The sensor in FHF05 is a thermopile. This thermopile measures the temperature
difference across the polyimide body of FHF05. Working completely passive, the
thermopile generates a small voltage that is a linear function of this temperature
difference. The heat flux is proportional to the same temperature difference divided by
the effective thermal conductivity of the heat flux sensor body.
Using FHF05 is easy. For readout the user only needs an accurate voltmeter that works
in the millivolt range. To convert the measured voltage, U, to a heat flux Φ, the voltage
must be divided by the sensitivity S, a constant that is supplied with each individual
sensor.
Φ = U/S (Formula 2.1.1)
Figure 2.1 The general working principle of a heat flux sensor. The sensor inside FHF05
is a thermopile. A thermopile consists of a number of thermocouples, each consisting of
two metal alloys (marked 1 and 2), electrically connected in series. A single
thermocouple generates an output voltage that is proportional to the temperature
difference between its hot- and cold joints. Putting thermocouples in series amplifies the
signal. In a heat flux sensor, the hot- and cold joints are located at the opposite sensor
surfaces (4 and 5). In steady state, the heat flux (6) is a linear function of the
temperature difference across the sensor and the average thermal conductivity of the
sensor body (3). The thermopile generates a voltage output proportional to the heat flux
through the sensor. The exact sensitivity of the sensor is determined at the manufacturer
by calibration, and can be found on the product certificate that is supplied with each
sensor.
5
4
321
6

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Figure 2.2 Heat flux from the back side to the front side generates a positive voltage
output signal. The dot on the foil indicates the front side.
All FHF05’s are designed such that heat flux from the back side to the front side
generates a positive voltage output signal. The dot on the foil indicates the front side.
Unique features of the FHF05 series include flexibility (bending radius ≥ 7.5 x 10-3 m), low
thermal resistance, a wide temperature range, a fast response time, IP67 protection class
rating (essential for outdoor application), and the inclusion of thermal spreaders to reduce
thermal conductivity dependence.

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All FHF05’s are calibrated under the following reference conditions:
•conductive heat flux (as opposed to radiative or convective heat flux)
•homogeneous heat flux across the sensor and guard surface
•room temperature
•heat flux in the order of 300 or 600 W/m2generated with our HTR02 series
•mounted on aluminium heat sink
FHF05 has been calibrated using a well-conducting metal heat sink, representing a
typical industrial application, at 20 °C and exposing it to a conductive heat flux. When
used under conditions that differ from the calibration reference conditions, for example at
extremely high or low temperatures, or exposed to radiative flux, the FHF05 sensitivity to
heat flux may be different than stated on the certificate. In such cases, the user may choose:
•not to use the sensitivity and only perform relative measurements / monitor changes
•reproduce the calibration conditions by mounting the sensor on, or between metal foils
•design a dedicated calibration experiment, for example using a foil heater which
generates a known heat flux
•correct the sensitivity for the temperature depence. See appendix 7.6 for more
information
•apply our BLK black sticker to the sensor surface to absorb radiation
•apply our GLD gold sticker to the sensor surface to reflect radiation
The user should analyse his own experiment and make his own uncertainty evaluation.
The FHF05 rated temperature range for continuous use is -70 to +120 °C, for short
intervals, peak temperatures -160 to +150 °C are allowed. Please contact Hukseflux
when measuring at -160 °C. Prolonged exposure to temperatures near +150 °C will
accelerate the ageing process.

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3Specifications of FHF05 series
3.1 Specifications of FHF05 series
FHF05 measures the heat flux density through the surface of the sensor. This quantity,
expressed in W/m2, is called heat flux. Working completely passive, using a thermopile
sensor, FHF05 generates a small output voltage proportional to this flux. It can only be
used in combination with a suitable measurement system.
Table 3.1.1 Specifications of FHF05 series (continued on next pages)
FHF05 SERIES SPECIFICATIONS
Sensor type
foil heat flux sensor
Sensor type according to ASTM
heat flow sensor or heat flux transducer
Measurand
heat flux
Measurand in SI units
heat flux density in W/m2
Measurement range
(-10 to +10) x 103W/m2 at heat sink temperature 20 °C
see appendix for detailed calculations
Sensitivity per dimension (nominal)
FHF05-10X10
1 x 10-6 V/(W/m2)
FHF05-15X30
3 x 10-6 V/(W/m2)
FHF05-50X50
13 x 10-6 V/(W/m2)
FHF05-15X85
7 x 10-6 V/(W/m2)
FHF05-85X85
50 x 10-6 V/(W/m2)
Directional sensitivity
heat flux from the back side to the front side (side with
the dot) generates a positive voltage output signal
Assymetry
< 2 %
Increased sensitivity
multiple sensors may be put electrically in series. The
resulting sensitivity is the sum of the sensitivities of
the individual sensors
Expected voltage output
(-100 to +100) x 10-3 V
turning the sensor over from one side to the other will
lead to a reversal of the sensor voltage output
Measurement function / required
programming
Φ= U/S
Required readout
1 differential voltage channel or 1 single ended
voltage channel, input resistance > 106Ω
Optional readout
1 temperature channel
Rated load on wires
≤1.6 kg
Rated bending radius
≥7.5 x 10-3 m
Rated temperature range,
continuous use
-70 to +120 °C
Rated temperature range,
short intervals
-160 to +150 °C
(contact Hukseflux when measuring at -160 °C)
Temperature dependence
< 0.2 %/°C
Non-linearity
< 5 % (0 to 10 x 10³ W/m²)
Solar absorption coefficient
0.75 (indication only)
Thermal conductivity dependence
negligible, < 3 %/(W/m·k) from 270 to 0.3 W/m·K
Sensor length and width
FHF05-10X10
(10 x 10) x 10-3 m
FHF05-15X30
(15 x 30) x 10-3 m
FHF05-50X50
(50 x 50) x 10-3 m
FHF05-15X85
(15 x 85) x 10-3 m
FHF05-85X85
(85 x 85) x 10-3 m

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Table 3.1.1 Specifications of FHF05 series (started on previous pages)
Sensing area
FHF05-10X10
0.64 x 10-4 m2
FHF05-15X30
2.70 x 10-4 m2
FHF05-50X50
12.96 x 10-4 m2
FHF05-15X85
7.10 x 10-4 m2
FHF05-85X85
47.70 x 10-4 m2
Sensing area length and width
FHF05-10X10
(8 x 8) x 10-3 m
FHF05-15X30
(10 x 27) x 10-3 m
FHF05-50X50
(36 x 36) x 10-3 m
FHF05-15X85
(10 x 71) x 10-3 m
FHF05-85X85
(70 x 71) x 10-3 m
Passive guard area
FHF05-10X10
0.36 x 10-4 m2
FHF05-15X30
2.25 x 10-4 m2
FHF05-50X50
12.04 x 10-4 m2
FHF05-15X85
5.65 x 10-4 m2
FHF05-85X85
22.55 x 10-4 m2
Guard width to thickness ratio
FHF05-10X10
2.5
FHF05-15X30
6.25
FHF05-50X50
17.5
FHF05-15X85
6.25
FHF05-85X85
18.75
Sensor thickness
0.4 x 10-3 m
Sensor thermal resistance
11 x 10-4 K/(W/m2)
Sensor thermal conductivity
0.36 W/(m·K)
Response time (95 %)
3 s
Sensor resistance range per dimension
FHF05-10X10
20 –60 Ω
FHF05-15X30
50 –90 Ω
FHF05-50X50
200 –300 Ω
FHF05-15X85
100 –180 Ω
FHF05-85X85
800 –1300 Ω
Required sensor power
zero (passive sensor)
Temperature sensor
type T thermocouple
Temperature sensor accuracy
± 5 % (of temperature in ˚C), see appendix 7.8 for
directions how to reduce the uncertainty to ± 2 %
which is the normal specification for Class 2
thermocoupes
Standard wire length
2 m
Optional wire length
0, 5 or 10 m
Wiring
3 x copper and 1 x constantan wire, AWG 28, solid
core, bundeled with a MFA sheath
Cable diameter
2 x 10-3 m
Marking
dot on foil indicating front side of the heat flux sensor;
1 x label at end of FHF05’s cable, showing serial
number and sensitivity
IP protection class
IP67
Rated operating relative humidity range
0 to 100 %
Use under water
FHF05 is not suitable for continuous use under water
Gross weight including 2 m wires
approx. 0.5 kg
Net weight including 2 m wires
approx. 0.5 kg

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Table 3.1.1 Specifications of FHF05 series (started on previous pages)
INSTALLATION AND USE
Typical conditions of use
in experiments, in measurements in laboratory and
industrial environments. Exposed to heat fluxes for
periods of several minutes to several years. Connected
to user-supplied data acquisition equipment. Regular
inspection of the sensor. Continuous monitoring of
sensor temperature. No special requirements for
immunity, emission, chemical resistance.
Recommended number of sensors
2 per measurement location
Installation
see Chapter 5 on installation for recommendations
Bending
see Section 5.2 on installation on curved surfaces
Cable extension
see Appendix 7.1 on cable extension, or order sensors
with longer cable length
Sensor foil installation
see Appendix 7.2 on installation of FHF05 without
wiring, without connection block
CALIBRATION
Calibration traceability
to SI units
Product certificate
included (showing calibration result and traceability)
Calibration method
method HFPC, according to ASTM C1130 - 21
Calibration hierarchy
from SI through international standards and through
an internal mathematical procedure
Calibration uncertainty
< ± 5 % (k = 2)
Recommended recalibration interval
2 years
Calibration reference conditions
20 °C, heat flux of 300 (models -15X85 and -85X85)
or 600 (models -10X10, -15X30 and 50X50) W/m2,
mounted on aluminium heat sink, thermal conductivity
of the surrounding environment 0.0 W/(m·K)
Validity of calibration
based on experience the instrument sensitivity will not
change during storage. During use the instrument
“non-stability” specification is applicable. When used
under conditions that differ from the calibration
reference conditions, the FHF05 sensitivity to heat flux
may be different than stated on its certificate. See the
chapter on instrument principle for suggested solutions
Field calibration
is possible by comparison to a calibration reference
sensor. Usually mounted side by side, alternative on
top of the field sensor. Preferably reference and field
sensor of the same model and brand. Typical duration
of test > 24 h
MEASUREMENT ACCURACY
Uncertainty of the measurement
statements about the overall measurement
uncertainty can only be made on an individual basis.
VERSIONS / OPTIONS
With longer cable length
option code = cable length in metres
Without cable, without connection block
calibrated FHF05 sensor foil
to be soldered / connected by the user
see appendix for more information
With black sticker applied
BLK sticker applied to the sensor at the factory to
absorb radiation
With gold sticker applied
GLD sticker applied to the sensor at the factory to
reflect radiation
ACCESSORIES

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Hand-held read-out unit
LI19 handheld read-out unit / datalogger
NOTE: LI19 does not measure temperature, only heat flux
Separate foil heater
HTR02 general-purpose heater, that can be used for test
and calibration purposes
Separate cable
cable with 3 x copper and 1 x constantan wire, AWG
28, solid core, bundeled with a MFA sheath
availabel in 2, 5 or 10 m length
Separate black stickers
BLK sticker to absorb radiation, to be applied by the user
Separate gold sticker
GLD sticker to reflect radiation, to be applied by the user

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3.2 Dimensions of FHF05 series
Figure 3.2.1 Models FHF05 15X30 and 15X85; Y = 27 or 70, dimensions in x 10-3 m
(1) sensing area with thermal spreaders
(2) passive guard
(3) type T thermocouple
(4) dot indicating front side
(5) connection block for strain relief
(6) cable, standard length C = 2 m

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Figure 3.2.2 Models FHF05 10X10, 50X50 and 85X85 heat flux sensor; Y = 8, 36 or 70,
dimensions in x 10-3 m
(1) sensing area with thermal spreaders
(2) passive guard
(3) type T thermocouple
(4) dot indicating front side
(5) connection block for strain relief
(6) cable, standard length C = 2 m

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4Standards and recommended practices
for use
FHF05 series should be used in accordance with recommended practices.
4.1 Heat flux measurement in industry
FHF05 sensors are often used to measure on industrial walls and metal surfaces,
estimating the installation’s energy balance and the thermal transmission of walls.
Typically the total measuring system consists of multiple heat flux- and temperature
sensors. In many cases heat flux sensors are used for trend monitoring.In such cases
reproducibility is more important than absolute measurement accuracy.
Figure 4.1.1 Example of model FHF05-85X85 foil heat flux sensor being installed for
measurement on an industrial pipe. The sensor is mounted on a well-prepared curved
surface.