Hukseflux FHF04 User manual

Copyright by Hukseflux | manual www.hukseflux.com | [e-mail]
USER MANUAL FHF04
Foil heat flux sensor with thermal spreaders, flexible,
50 x 50 mm, with temperature sensor
Hukseflux
Thermal Sensors
Copyright by Hukseflux | manual v2101 | www.hukseflux.com | [e-mail]

FHF04 manual v2101 2/39
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 FHF04 8
1.2 Included items 8
1.3 Quick instrument check 9
2Instrument principle and theory 10
3Specifications of FHF04 13
3.1 Specifications of FHF04 13
3.2 Dimensions of FHF04 16
4Standards and recommended practices for use 17
4.1 Heat flux measurement in industry 17
5Installation of FHF04 18
5.1 Site selection and installation 18
5.2 Installation on curved surfaces 20
5.3 Electrical connection 21
5.4 Requirements for data acquisition / amplification 24
6Maintenance and trouble shooting 25
6.1 Recommended maintenance and quality assurance 25
6.2 Trouble shooting 26
6.3 Calibration and checks in the field 27
7Appendices 29
7.1 Appendix on wire extension 29
7.2 Appendix on installation of FHF04 sensor foil 30
7.3 Appendix on using FHF04 with BLK – GLD sticker series 33
7.4 Appendix on standards for calibration 34
7.5 Appendix on calibration hierarchy 34
7.6 Appendix on correction for temperature dependence 35
7.7 Appendix on measurement range for different temperatures 36
7.8 Appendix on temperature measurement accuracy 37
7.9 EU declaration of conformity 38

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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
FHF04 is the latest standard model for general-purpose heat flux measurement.
Significantly thinner and more flexible, FHF04 replaces earlier models FHF01 and FHF02.
FHF04 is very versatile: it has an integrated temperature sensor and thermal spreaders
to reduce thermal conductivity dependence. It is applicable over a temperature range
from –70 to +120 °C. FHF04 measures heat flux from conduction, radiation and
convection. Optionally, black BLK and gold GLD stickers are available to separately
determine heat transport by radiation and convection.
FHF04 measures heat flux through the object in which it is incorporated or on which it is
mounted, in W/m2. The sensor in FHF04 is a thermopile. This thermopile measures the
temperature difference across FHF04’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 FHF04 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 FHF04 foil heat flux sensor with thermal spreaders: thin, flexible and versatile
Using FHF04 is easy. It can be connected directly to commonly used data logging systems.
The heat flux in W/m2is calculated by dividing the FHF04 output, a small voltage, by the
sensitivity. The sensitivity is provided with FHF04 on its product certificate.

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FHF04 foil heat flux sensor has unique features and benefits:
•flexible (bending radius ≥ 7.5 x 10-3 m)
•low thermal resistance
•wide temperature range
•fast response time
•large guard area
•integrated type T thermocouple
•robustness, including wiring and metal connection block, may be used as strain
relief between sensor and wires
•IP protection class: IP67 (essential for outdoor application)
•integrated thermal spreaders for low thermal conductivity dependence
Equipped with a metal connection block, which may serve as strain relief, and with
potted protective covers on both sides so that moisture does not penetrate, FHF04 has
proven to be very robust and stable.
Figure 0.2 FHF04 foil heat flux sensor being installed to measure heat flux on a pipe
FHF04 calibration is traceable to international standards. The factory calibration method
follows the recommended practice of ASTM C1130 - 17. When used under conditions that
differ from the calibration reference conditions, the FHF04 sensitivity to heat flux may be
different than stated on its certificate. See Chapter 2 in this manual for suggested
solutions.
Would you like to study energy transport / heat flux in detail? Hukseflux helps taking this
measurement to the next level: order FHF04 with radiation-absorbing black and radiation-
reflecting gold stickers. You can then measure convective + radiative flux with one, and
convective flux only with the other. Subtract the 2 measurements and you have radiative

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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.
Figure 0.3 FHF04 heat flux sensor: with BLK-5050 and GLD-5050 stickers
See also:
•model FHF04SC for a self-calibrating version of FHF04
•model FHF03, our most economical foil heat flux sensor
•model HFP01 for increased sensitivity (also consider putting two or more FHF04s in
series)
•BLK - GLD sticker series to separate radiative and convective heat fluxes
•Hukseflux offers a complete range of heat flux sensors with the highest quality for
any budget
absorbs radiation
reflects radiation

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1Ordering and checking at delivery
1.1 Ordering FHF04
The standard configuration of FHF04 is with 2 metres of wire.
Common options are:
•with 5 metres wire length
•without wiring, without metal connection block
•with LI19 hand-held read-out unit / datalogger; NOTE: LI19 measures heat flux only,
not temperature
•BLK-5050 black sticker (to measure radiative as well as convective heat flux)
•GLD-5050 gold sticker (to measure convective heat flux only)
•BLK - GLD sticker series can also be ordered pre-applied at the factory
1.2 Included items
Arriving at the customer, the delivery should include:
•heat flux sensor FHF04 with wires of the length as ordered
•product certificate matching the instrument serial number
Figure 1.2.1 FHF04’s serial number and sensitivity are visible on the metal connection
block. FHF04 is delivered with bundled wiring.

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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 sensor serial number and sensitivity on the sticker on the metal connection
block 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 0.1 Ω/m. Typical resistance should be the nominal sensor resistance of 200 Ω
plus 0.2 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 0.1 Ω/m, for the constantan wiring this is 2.5 Ω/m.
Typical resistance should be the nominal thermocouple resistance of 2.5 Ω plus 2.6 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.
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
FHF04’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”.
FHF04 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 FHF04 is a thermopile. This thermopile measures the temperature
difference across the polyimide body of FHF04. 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 FHF04 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 FHF04
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.
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