Hukseflux

Thermal Sensors

USER MANUAL BLK - GLD
STICKER SERIESBlack and gold stickers for measuring
convective and radiative heat flux separately

Copyright by Hukseflux | manual v2216 | www.hukseflux.com | info@hukseflux.com

Cautionary statements
Cautionary statements are subdivided into four categories: danger, warning, caution andnotice 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 orserious physical injuries.

CAUTION
Failure to comply with a caution statement may lead to risk of minor ormoderate physical injuries.

NOTICE
Failure to comply with a notice may lead to damage to equipment or may
compromise reliable operation of the instrument.

BLK - GLD sticker series manual v2216

2/47

Contents
Cautionary statements
Contents
List of symbols
Introduction
1
Ordering and checking at delivery
1.1
Ordering BLK – GLD stickers
1.2
Included items
2
Instrument principle and theory
2.1
Introduction
2.2
Normal use: moderate-accuracy and comparative measurements
3
Advanced use: high-accuracy measurements
3.1
Introduction
3.2
Spectral properties of BLK and GLD stickers
3.3
BLK and GLD sensors on the same heat sink
3.4
BLK and GLD sensors at different temperatures
3.5
Surface temperature correction at high flux levels
3.6
Optional correction for sensor temperature dependence
3.7
Working with high colour temperature sources; the Sun, Xenon lamps
4
Examples of BLK and GLD in use
4.1
Outgoing radiation heat flux on metallic / reflective surfaces
4.2
Sources covering part of the sensor field of view; the view factor
4.3
Heat flux measurement to characterise ovens, thermal profiling
5
Specifications of BLK – GLD sticker series
5.1
Specifications of BLK – GLD stickers
5.2
Dimensions of BLK – GLD stickers
6Installation of BLK – GLD sticker series
6.1
Application procedure
6.2
Site selection and sensor installation
7
Maintenance and trouble shooting
7.1
Recommended maintenance and quality assurance
7.2
Trouble shooting
7.3
Calibration and on-site checks
8
Appendices8.1
Reflection versus wavelength and source temperature
8.2
EU declaration of conformity

BLK - GLD sticker series manual v2216

2
3
4
5
8
8
10
11
11
13
14
14
14
16
20
21
23
24
25
25
26
28
32
32
34
36
36
38
40
40
42
42
43
43
46

3/47

List of symbols
Quantities

SymbolUnit

Heat flux
Voltage
Sensitivity
Temperature
Temperature dependence of sensitivity
Thermal resistance per unit area
Heat transfer coefficient by convection
Area
Reflection factor
AbsorbanceEmissivity
Stefan-Boltzmann constant: 5.67 x 10-8
Optical view factor
Angle of incidence
Solid angle

Φ
U
S
T
TD
Rthermal,A
Ctr
A
r
α
ε
σ
f
θ
SA

W/m²
V
V/(W/m2)°C or K%/K
K/(W/m²)(W/m2)/Km2
W/m²·K4°
sr

Subscripts
Property of sensor
Property of heat sink
Property of a radiative source
Measured radiative heat flux
Measured convective heat flux
Sensor with black sticker
Sensor with gold sticker
Property of ambient air
Property of ambient environment
Total
Emitted radiative flux
Incoming radiative flux at the sensor position
Absorbed radiative flux
Reflected radiative flux

sensorsink
sourceradiative
convective
BLK
GLD
air
ambient
total
emittedincoming
absorbedreflected

Abbreviations
Ultraviolet
Visible light
Near-infrared
Far-infrared

BLK - GLD sticker series manual v2216

UV
VIS
NIR
FIR

4/47

Introduction
Heat flux measurement is a powerful tool to gain insights into processes involving
thermal energy. Heat is transported to an object by convection and radiation. Studying
thermal processes, the cause of temperature changes or heat transport, you may wish to
separate radiative and convective heat flux. This is now possible with the BLK – GLD
sticker series, designed to be used with a wide range of our market-leading heat flux
sensors. The BLK black stickers absorb all radiation and are sensitive to both radiativeand convective heat flux, while the GLD gold reflective stickers reflect all radiation andare sensitive to convective heat flux only. Applying BLK and GLD stickers, on two
separate heat flux sensors, makes it possible to calculate the contributions of radiativeand convective heat flux:Φradiative + Φconvective = Φtotal = ΦBLK

Φconvective = ΦGLD

Φradiative = ΦBLK − ΦGLD

BLK – GLD stickers have unique features and benefits:•••

makes it possible to perform convective and radiative heat flux measurements
available as accessory for the five models of the FHF05 series and HFP01 heat flux
sensors
designed to be applied by the user

Figure 0.1 From left to right: model FHF05-50X50 heat flux sensor, FHF05-50X50 with
BLK-50X50 sticker, and FHF05-50X50 with GLD-50X50 sticker. BLK – GLD stickers are alsoavailable for other dimensions of the FHF05 series and HFP01 heat flux sensors. The BLK
black absorbing stickers will absorb all radiation and are sensitive to both radiative andconvective heat flux, while the GLD gold reflective stickers reflect all radiation and are
sensitive to convective heat flux only.

BLK - GLD sticker series manual v2216

5/47

Figure 0.2 Working with BLK - GLD stickers: measuring the radiative and convective
heat fluxes on an espresso machine.
BLK – GLD stickers are easy to use:
They are designed to be applied by the user but can optionally also be pre-applied at thefactory. Applying a sticker to a heat flux sensor does not change the sensitivity of thesensor, so no additional calibration is required. Using the reliable measurement technology
behind our heat flux sensors, separating convective and radiative heat flux has never beeneasier.

Figure 0.3 BLK – GLD sticker series is a range of accessories for use with Hukseflux heat
flux sensors of the FHF05 series and HFP01. The stickers have matching sizes and aredesigned to be applied by the user to the sensor.

BLK - GLD sticker series manual v2216

6/47

There is restriction to use BLK and GLD stickers: in particular if there is a notable amountof solar radiation, the GDL sticker will absorb a significant part of it.
NOTICE
Treat BLK and GLD stickers with care. Avoid abrasive action. Clean gently with
soft cloth and if needed with demi-water. The gold layer of the GLD sticker isextremely thin and may easily be rubbed off.

NOTICEThe GLD sticker will not perfectly reflect radiation from sources withblackbody temperature higher than 4000 K. Solar radiation is in this category.
When in doubt, consult this manual or Hukseflux.

See also:
•
•
•
•
•
•

BLK – GLD sticker application instruction video on our YouTube channel
FHF05 series general-purpose heat flux sensor
FHF05SC series a self-calibrating version of the FHF05 seriesmodel HFP01 for increased sensitivity
heater HTR02 series, for calibration and verification of performance of FHF-type
sensors
view our complete range of heat flux sensors

Figure 0.4 Overview of BLK-GLD stickers series: black absorbing stickers and gold
reflective stickers matching FHF05 series and HFP01 heat flux sensors. They are designed
to be applied by the user but can optionally also be pre-applied at the factory. The figure
shows, from left to right, the stickers GLD and BLK on FHF05-10X10, FHF05-15X30,
FHF05-50X50, FHF05-15X85 and FHF05-85X85. BLK-GLD sticker series is also available
for model HFP01 and FHF05SC series.

BLK - GLD sticker series manual v2216

7/47

1

Ordering and checking at delivery

1.1

Ordering BLK – GLD stickers

The BLK – GLD sticker series is a range of accessories for use with Hukseflux heat flux
sensors of FHF05(SC) series and HFP01.
The ordering codes of the different versions in the series are BLK-10X10, BLK-15X30, BLK50X50, BLK-15X85, BLK-85x85, BLK-80, GLD-10X10, GLD-15X30, GLD-50X50, GLD15X85, GLD-85X85 and GLD-80.
Table 1.1.1 Overview of versions in the BLK – GLD sticker series
BLK versions
BLK-10X10

Black absorbing sticker to measure convective + radiative heat flux, to be usedwith FHF05(SC)-10X10 heat flux sensors

BLK-15X30

Black absorbing sticker to measure convective + radiative heat flux, to be usedwith FHF05(SC)-15X30 heat flux sensors

BLK-50X50

Black absorbing sticker to measure convective + radiative heat flux, to be usedwith FHF05(SC)-50X50 heat flux sensors

BLK-15X85

Black absorbing sticker to measure convective + radiative heat flux, to be usedwith FHF05(SC)-15X85 heat flux sensors

BLK-85X85

Black absorbing sticker to measure convective + radiative heat flux, to be usedwith FHF05(SC)-85X85 heat flux sensors

BLK-80Black absorbing sticker to measure convective + radiative heat flux, to be usedwith HFP01 heat flux sensor

GLD versions
GLD-10X10

Gold reflective sticker to measure convective heat flux only, to be used with
FHF05(SC)-10X10 heat flux sensors

GLD-15X30

Gold reflective sticker to measure convective heat flux only to be used with
FHF05(SC)-1530 heat flux sensors

GLD-50X50

Gold reflective sticker to measure convective heat flux only, to be used with
FHF05(SC)-50X50 heat flux sensors

GLD-15X85

Gold reflective sticker to measure convective heat flux only, to be used with
FHF05(SC)-15X85 heat flux sensors

GLD-85X85

Gold reflexive sticker to measure convective heat flux only, to be used with
FHF05-85X85 heat flux sensors

GLD-80Gold reflective sticker to measure convective heat flux only, to be used with
HFP01 heat flux sensor

A common option is:

BLK - GLD sticker series manual v2216

8/47

•

pre-application of the sticker to the sensor(s) of your choice at the factory

When opting for pre-application at the factory, please use the following ordering code:
product code sensor with cable length indicated + product code sticker
example: HFP01-05-GLD-80
for model HFP01 with 5 meters of cable and a pre-applied gold sticker

BLK - GLD sticker series manual v2216

9/47

1.2

Included items

Arriving at the customer, the delivery should include:•••

BLK – GLD sticker version(s) as orderedapplication procedure instruction sheet
prostrated IPA (Isopropyl Alcohol) wipeSee the instruction sheet included with your delivery, the instruction movie on our
YouTube channel or Section 4.1 of this manual for instructions how to apply the BLK –GLD stickers to your sensor.
When opting for pre-applied BLK – GLD stickers, the delivery should include:••

heat flux sensor with sticker applied, with cable of the length as ordered
product certificate matching the instrument serial number

Figure 1.2.1 GLD and BLK stickers pre-applied to their matching sensors at the factory

BLK - GLD sticker series manual v2216

10/47

2

Instrument principle and theory

2.1

Introduction

BLK and GLD stickers series are accessories to FHF05 series and HFP01 heat flux
sensors. These stickers allow the heat flux sensors to be used to separately measureradiative and convective heat flux.
As a first approximation, BLK black stickers absorb all radiation, as Figure 2.1 shows.

Figure 2.1.1 BLK black stickers absorb all radiation
In contrast to BLK black stickers, GLD gold stickers as a first approximation reflect allradiation.

Figure 2.1.2 GLD gold stickers reflect all radiation

BLK - GLD sticker series manual v2216

11/47

BLK black stickers are sensitive both to radiative and convective heat flux, whereas GLD
gold stickers, reflecting all radiation, are sensitive to convective heat flux only. See
Figure 2.1.3.

Figure 2.1.3 Both BLK and GLD stickers are sensitive to convective heat flux
Summarising, radiative and convective heat flux are absorbed by the black sticker. The
absorbed heat flows through the heat flux sensor, creating a temperature difference
across the thermopile detector inside the heat flux sensor. This thermopile generates asmall voltage proportional to the sum of the radiative and convective heat flux.
Radiative heat flux is reflected by the gold sticker, convective heat flux is absorbed. The
absorbed heat flows through the heat flux sensor, generating a small voltage
proportional to the convective heat flux.
The proportionality factor, the ratio of heat flux sensor output voltage to heat flux, iscalled the sensitivity S in V/(W/m²). This is determined individually for the heat flux
sensor by calibration and reported on its product certificate.
Applying a sticker to a heat flux sensor does not change the sensitivity of the heat flux
sensor.

BLK - GLD sticker series manual v2216

12/47

2.2

Normal use: moderate-accuracy and comparative
measurements

As a first approximation, you may assume that both sensors are at the same
temperature and have perfect absorption and emission. This approach leads tomoderate-accuracy results. These may be sufficient for the average user.
This moderate-accuracy approach is also often used to compare two situations, forexample with a source switched [on] or [off]. Furthermore, it is useful to estimate
orders of magnitude of heat flux as a starting point for high-accuracy measurements.
For moderate-accuracy measurements the following formulas are used:Φradiative + Φconvective = Φtotal = ΦBLK

(2.1.1)

Φradiative = ΦBLK − ΦGLD

(2.1.3)

Φ = U/S(2.1.4)

Φconvective = ΦGLD

(2.1.2)The heat flux Φ in W/m² passing through- and measured by a heat flux sensor iswhere [U] is the heat flux sensor voltage output, and [S] the sensitivity found on thesensor calibration certificate.
Chapter 3 explains what should be done to attain a high-accuracy measurement.

BLK - GLD sticker series manual v2216

13/47

3

Advanced use: high-accuracy
measurements

3.1

Introduction

The following sections explain what should be done to attain a high-accuracy
measurement with BLK and GLD stickers.
For high accuracy measurement it is essential to understand that:• absorption and reflection of both BLK and GLD stickers may not be perfect• a sensor with a BLK black sticker not only receives radiation, but also emits radiation
depending on its own temperature. What is measured is the net result of incoming
and emitted radiation• the surface temperature of a sensor is not the same as the measured temperature.
The difference between the measured sensor body and heat sink temperaturedepends on the heat flux. The difference can be calculated from temperature, heat
flux and thermal resistance of the sensor. At high heat fluxes this temperature
difference is significant.
• the sensitivity of a heat flux sensor is not a constant. It changes with temperature.
Calibration is performed at 20 °C. At operating temperatures far away from thecalibration temperature, you may compensate for this effect.
• radiation of high colour-temperature sources is not perfectly reflected by the GLD
sensorSection 3.2 gives more details on the BLK and GLD spectral properties. The further
sections treat typical mathematical treatment of measurement results to compensate forthe above effects.

3.2

Spectral properties of BLK and GLD stickers

In high accuracy measurement you may correct for non-perfect absorption and emission.
This section gives the numbers to work with. See also the appendix on the subject.

3.2.1 Reflection
In an ideal scenario, a black sticker reflects no radiation across all wavelengths and agold sticker reflects all radiation across all wavelengths. In reality, the reflection of bothstickers depends on the wavelength of the incoming radiation.
The BLK black sticker has an average reflection of 3 % (rBLK = 0.03) in the UV, visible,
near-infrared and far-infrared spectrum.
The GLD gold sticker has a reflection of about 35 % (rGLD = 0.35) in the UV spectrum,
which increases through the visible spectrum to an average reflection value of 98 %(rBLK = 0.98) in the near-infrared and the far-infrared.

BLK - GLD sticker series manual v2216

14/47

1
0.9

reflection factor

0.8
0.7
0.6
GLD

0.5
0.4

BLK

0.3
0.2
0.1
0

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

wavelength [nm]Figure 3.2.1.1 BLK and GLD reflection factors as a function of wavelength
Typical values of the average reflection factors for common radiation sources are given intable 2.2.1.1.
For more details on spectral properties of the stickers, see the Appendix on the subject.
Table 3.2.1.1 Typical reflection factor for common radiation sources
RADIATION SOURCEUV radiation
Solar radiation, Xenon lamps(colour temperature 6000 K)
Halogen and infrared lamps, industrial heaters(colour temperature < 4000 K)
Low temperature infrared sources such as radiant heaters,
stoves, 300 to 600 ˚C
Objects at room temperature, - 40 to + 70 ˚C

rBLK
0.02
0.02

rGLD
0.35
0.80

0.03

0.97

0.05

0.99

0.11

0.99

3.2.2 absorption and emissivity
In certain applications, absorption and emissivity are the relevant spectral properties
instead of reflection.
Absorption α is the amount of energy absorbed by an object.
αBLK = 1 - rBLKαGLD = 1 - rGLD

BLK - GLD sticker series manual v2216

15/47

Emittance is the amount of thermal energy emitted by an object. Numerically, emissivity
is the same as absorption.
εBLK = αBLKεGLD = αGLD
Table 3.2.2.1 Typical absorption factors for common radiation sources
RADIATION SOURCEUV radiation
Solar radiation, Xenon lamps(colour temperature 6000 K)
Halogen and infrared lamps, industrial heaters(colour temperature < 4000 K)
Low temperature infrared sources such as radiant heaters,
stoves, 300 to 600 ˚C
Objects at room temperature, - 40 to + 70 ˚C

3.3

αBLK
0.98
0.98

αGLD
0.65
0.20

0.97

0.03

0.95

0.01

0.89

0.01

BLK and GLD sensors on the same heat sink

If possible, we recommend mounting the two sensors, BLK and GLD, on the same heatsink. This makes analysis easy because they then have - at least approximately, which is
sufficient - the same temperature, and thus:
TBLK = TGLD

(3.3.1)

To measure radiative and convective heat flux, preferably:••••

apply a BLK black sticker on a first heat flux sensor
apply a GLD gold sticker on another heat flux sensor
place the two heat flux sensors side by side, on the same heat sink so that they havethe same heat sink (and sensor) temperature.
a heat sink may be a metal plate, for example an aluminium plate of at least 1 mm
thickness, or, in case a larger heat capacity is required, a thicker plate. We thenassume there is no significant temperature difference of the heat sink between
sensors (difference < 2 ˚C)

BLK - GLD sticker series manual v2216

16/47

Measure:••••Tamb, ambient air temperature
TGLD, the heat sink temperature
ΦBLK , heat flux measured by the black heat flux sensor (output voltage divided bysensitivity)
ΦGLD , heat flux measured by the gold heat flux sensor (output voltage divided bysensitivity)

Typical boundary conditions to keep in mind are:
•
•
•
•
•

valid measurements require steady state conditions: temperature and flux do notchangeno solar radiation or other sources with high colour temperature (see the section on
working with high temperature sources / solar radiation)
heat fluxes below a level that surface temperature significantly increases (see thesection on correction of sensor surface temperature)
spectral corrections are made based on the tables in the section about spectral
properties)
sensor temperatures at a level that temperature dependence is not corrected (seeappendix on temperature dependence)

Applying a sticker does not alter the working principle of the heat flux sensor. The
original sensitivity S, as specified on the sensor calibration certificate, is still valid.
For most VIS, IR and FIR radiation sources the GLD sticker is a perfect reflector. This
does not apply to solar and Xenon lamp sources (see tables in 3.2). In case the sources
have a low colour temperature, lower than 1000 ˚C, we assume that the reflection factorof GLD, while actually 0.99, is 1. See the section on sources with high colour
temperature and the appendix on reflection and absorption how to deal with exceptionalsources.
rGLD = 1(3.3.2)The heat flux Φ in W/m² passing through- and measured by a heat flux sensor isΦ = U/S(3.3.3)where [U] is the heat flux sensor voltage output, and [S] the sensitivity found on thesensor calibration certificate.

BLK - GLD sticker series manual v2216

17/47

3.3.1 Measurement of convective flux
The purpose is to calculate the convective heat flux Φconvective:••••

transferred by ambient air at a certain temperature and speed
to an object at the heat flux sensor location
to an object at the heat flux sensor temperature
to an object in the heat flux sensor plane (same surface orientation)

The heat flux due to convection is measured by the GLD sensor.
Φconvective = ΦGLD = UGLD/SGLD(3.3.1.1)

3.3.2 Characterising a convective source: Tair and heat transfer coefficient Ctr
Properties of a convective source properties are the convective ambient air temperature
Tair and the convective heat transfer coefficient Ctr. Knowing Ctr, the convective heattransfer to a similarly oriented surface in the same airflow may be calculated.
Note that the convective heat transfer coefficient Ctr is not a function of the sensor
temperature, because the Φconvective is proportional to the difference (Tair - TGLD). Ctr is afunction of:••

air speed andthe interaction of the sensor surface with the air (orientation of the surface).

Ctr = Φconvective/(Tair - TGLD)(3.3.2.1)

Expected measured values of the heat transfer coefficient for air are between 5 to 20
W/(m²∙K) for natural thermal convection and up to 100 W/(m²∙K) for forced convection.
The convective heat transfer to a similarly oriented surface in the same airflow is:Φconvective, surface = Ctr∙(Tair - Tsurface)(3.3.2.2)

3.3.3 Measurement of incoming radiative flux
The purpose is to calculate the radiative heat flux Φincoming•••

emitted by the source
incoming to an object at the heat flux sensor location
to an object in the heat flux sensor plane (same surface orientation)

BLK - GLD sticker series manual v2216

18/47

As a first approximation we assume that the heat transfer by convection to the BLK and
GLD sensors is identical, because their surface temperatures are the same, see 2.3.1.
Φconvective = Φconvective BLK = Φconvective GLD(3.3.3.1)

The measured radiative flux ΦBLK is a net heat flux consisting of incoming flux from thesource, corrected for the absorption of the BLK coating αBLK, incoming for incoming radiation
Φincoming from the source at Tsource minus the (blackbody) radiation emitted by the sensor
at TBLK, corrected for the emission of the BLK coating, εBLK, emitted.
The net heat flux by radiation as measured by the BLK sensor
Φradiative BLK = ΦBLK - Φconvective GLD = (UBLK/SBLK) – (UGLD/SGLD)(3.3.3.2)

andΦradiative BLK= αBLK, incoming∙Φincoming - σ∙εBLK, emitted∙(TBLK +273)4(3.3.3.3)

This gives us the following formula to calculate the incoming flux:
Φincoming
3.3.3.1= (Φradiative BLK + σ∙εBLK, emitted∙(TBLK +273)4 )/αBLK, incoming(3.3.3.4)

Example 1: working around room temperature:

Consider the following boundary conditions:-40 ˚C < TBLK, Tsource < 70 ˚C(3.3.3.1.1)

We assume (see appendix on absorption and reflection):
εBLK, emitted = αBLK, incoming = 0.89

(3.3.3.1.2)

so thatΦincoming = 1.12∙Φradiative BLK + σ∙(TBLK + 273)4

3.3.3.2(3.3.3.1.3)

Example 2: sensor at room temperature and a uniform infra-red source

Consider the following boundary conditions:-40 ˚C < TBLK < 70 ˚C,
300 ˚C < Tsource < 600 ˚C

BLK - GLD sticker series manual v2216(3.3.3.2.1)(3.3.3.2.2)

19/47

We assume:
εBLK, emitted = 0.89

(3.3.3.2.3)

αBLK, incoming = 0.95

(3.3.3.2.4)

andΦincoming = (1.05∙Φradiative BLK + 0.94∙σ∙(TBLK + 273)4(3.3.3.2.5)

3.3.4 Characterising a radiative source: Tblackbody equivalent blackbody
temperature
The equivalent blackbody source temperature assumes that the heat flux sensors face•••

an imaginary, uniform blackbody source
over its full 180˚ field of view angle (or more correctly: 2Π sr solid angle)
with an emission of 1

εsource = 1(3.3.4.1)

The heat exchange is described by:σ∙εsource∙(Tblackbody + 273)4= (Φradiative + σ∙εBLK, emitted∙(TBLK + 273)4)/αBLK, incoming(3.3.4.2)

The equivalent blackbody source temperature is:
Tblackbody =((Φradiative + σ∙εBLK, emitted∙(TBLK + 273)4)/(σ∙εsource∙αBLK, incoming))1/4 - 273

3.4(3.3.4.3)

BLK and GLD sensors at different temperatures

In case TBLK and TGLD differ by more than 2˚C, this may have a significant impact onconvective exchange:|TBLK - TGLD| > 2(3.4.1)equation 3.3.3.2 must be corrected for differences in convective heat flux:Φradiative= ΦBLK - Φconvective GLD= (UBLK/SBLK) – (UGLD/SGLD)∙((Tair – TBLK)/(Tair - TGLD))(3.4.2)

From then on, the other equations of 3.3.3 may be used, possibly with the optionalcorrections of 3.5 and 3.6.

BLK - GLD sticker series manual v2216

20/47

3.5

Surface temperature correction at high flux levels

A similar correction as in 3.4 should also be considered when there is a large heat flux.
In that case the sensor surfaces may be hotter than the temperature measurement. The
correction depends on the heat flux Φ through the sensor and on the thermal resistance,
Rthermal,A, between the point at which the temperature is measured to the sensor surface.
Taking the BLK sensor as an example:
TBLK, corrected = TBLK + ΦBLK∙Rthermal,A, BLK= TBLK + (UBLK/SBLK)∙Rthermal,A, BLK(2.5.1)(2.5.2)

As in 3.4 we recommend correction if the difference between the corrected and measured
temperature is more than 2 ˚C.
Use correction if:|(UBLK/SBLK)∙Rthermal,A, BLK| > 2(2.5.3)3.5.1 Example: high heat flux correction with FHF05 series
A FHF05 model with a BLK or GLD sticker the thermal resistance is:
Rthermal,A = Rthermal,A, sensor +Rthermal,A, sticker = (11 + Rthermal,A, sticker) x 10-4

(3.5.1.1)

The location of temperature in the sensor is close to the surface where the sticker isapplied to. Roughly, this is at 1/6th of the total sensor thickness (0.4 x 10-3 m). The total
thermal resistance of the sensor is: Rthermal,A, sensor = 11 K/(W/m2). To account for thelocation of the temperature probe, a value of Rthermal,A, sensor temp location = 2 K/(W/m2) istaken.
The thermal resistance of the stickers is: Rthermal,A, sticker BLK = 10 x 10-4 K/(W/m2) and
Rthermal,A, sticker GLD = 3.5 x 10-4 K/(W/m2).
For a FHF05 model with a BLK sticker, the thermal resistance between the front surface
and the location of the thermocouple is:
Rthermal,A, sensor with BLK = (2 + 10) x 10-4

(3.5.1.2)

And for a FHF05 model with a GLD sticker, the thermal resistance between the front
surface and the location of the thermocouple is:
Rthermal,A, sensor with GLD = (2 + 3.5) x 10-4

(3.5.1.3)

And the corrected temperature for the sensor with BLK sticker becomes
TBLK, corrected = TBLK + 12 x 10-4∙ΦBLK= TBLK + 12 x 10-4∙(UBLK/SBLK)BLK - GLD sticker series manual v2216(3.5.1.4)(3.5.1.5)

21/47

The corrected temperature for the sensor with GLD sensor becomes
TGLD, corrected = TGLD + 5.5 x 10-4∙ΦGLD= TGLD + 5.5 x 10-4∙(UGLD/SGLD)(3.5.1.6)(3.5.1.7)

For FHF05 we recommend correcting if:
12 x 10-4∙(UBLK/SBLK) > 2 ˚C
5.5 x 10-4∙(UGLD/SGLD) > 2 °C

(3.5.1.8)(3.5.1.9)orΦBLK > 1667 W/m2
ΦGLD > 3635 W/m2

(3.5.1.10)(3.5.1.11)

In that case 3.3.3.2 becomes:
Φradiative= ΦBLK - Φconvective GLD= (UBLK/SBLK) – (UGLD/SGLD)∙((Tair - TBLK, corrected)/(Tair - TGLD))

BLK - GLD sticker series manual v2216(3.5.1.12)

22/47

3.6

Optional correction for sensor temperature dependence

The sensitivity of a heat flux sensor depends on the temperature of the sensor. For
example, the temperature dependence of the FHF05 series is specified as < 0.2 %/°C. At
higher temperatures, sensors usually are more sensitive. The order of magnitude is thesame for other sensor models. See the product manuals for up-to-date estimates oftemperature dependence for your sensor model.
The calibration reference temperature for Hukseflux sensors is 20 °C.
Temperature dependence may be corrected. This is worthwhile only if the error is of thesame order as calibration uncertainty, i.e., correction is recommended only if thecorrection > 4 %.
Apply corrections in case:
Tsensor < 0 ˚C,(3.6.1)orTsensor > 40 ˚C(3.6.2)

3.6.1 Correction of temperature dependence of the FHF05 series
To correct for the temperature dependence of the sensitivity of sensor model FHF05, use
the measurement function:
Φ = U/(S∙(1 + 0.002∙(Tsensor – 20)))(3.6.1.1)

with Φ the heat flux in W/m², U the sensor voltage output in V, S the sensitivity in
V/(W/m²) at 20 °C and Tsensor the sensor temperature.
S is shown on the product certificate and with some models on the sensor itself.

BLK - GLD sticker series manual v2216

23/47

3.7

Working with high colour temperature sources; the Sun,
Xenon lamps

The colour temperature of solar radiation and of Xenon lamps is around 6000 K. For thisspectrum, the GLD sticker no longer is a perfect reflector.
Heat flux of a direct solar beam on a clear sunny day may be in the order of 1000 W/m².
The absorption of GLD is 20 %, that of BLK 98 %, see section 2.2.
To correct for incoming solar radiation, use a pyranometer mounted in the same plane as
the heat flux sensor to correct the data. A pyranometer measures the solar heat flux
Φsolar in W/m².
If a pyranometer is not available, Φsolar may be estimated by carrying out an experimentshading and unshading the black sensor, as described in section 4.2.
Equation 3.3.1.1 is then corrected:
Φconvective = ΦGLD – 0.20∙Φsolar(3.7.1)

Φradiative BLK = ΦBLK - Φconvective – 0.98∙Φsolar(3.7.2)

BLK - GLD sticker series manual v2216

24/47

4

Examples of BLK and GLD in use

4.1

Outgoing radiation heat flux on metallic / reflective surfaces

Every object emits radiation. Only very hot objects, hotter than 400 ˚C, emit radiationthat is visible to the eye. Although not visible, heat flux sensors with BLK stickers emit asignificant amount of radiative energy too, while GLD stickers have a low emission sothat the emitted radiation is negligible.
In general: when performing measurements of emitted radiation from a surface, use aheat flux sensor with a sticker that matches the emissivity of the surface.
Most non-metallic surfaces, although they may have different colours (VIS spectral range
visible radiation for the human eye), are perfectly “black” in the FIR Far Infra-red; inother words, perfect absorbers (r = 0) / emitters (ε = 1). Metal surfaces are reflectors(also having a low emission) in VIS as well as FIR. Partial absorption in the FIR may befound in corroded or non-polished metal.
In this example we show that if you wish to measure radiation losses of a polished metal
surface, you get a representative measurement using a GLD sticker.
In figure 4.1.1, two sensors, one with a BLK sticker and one with a GLD sticker are
mounted on the surface of an espresso machine.
The surface temperature of the polished stainless-steel surface is approximately 45 ˚C.
The GLD sticker on the right has an emissivity like that of the espresso machine’s
polished metal surface. This can be seen using an infra-red camera; both the GLD sensor
and the metal surface appear bluish on the thermal image, having an apparent
temperature of 35 ˚C. The camera actually makes an error in its temperature
measurement because both surfaces do not emit radiation, while the camera assumes anemission of 1 for all surfaces. The actual temperature can be estimated from the image
taken of the BLK sensor, which has a near perfect emission εBLK of 1 and which appears
to be 45 ˚C. Both mounted on the same metal plate, so we may assume that the GLD
sensor has the same temperature.
The camera shows that the emissivity of the GLD sticker matches the emissivity of thestainless-steel surface reasonably well. A heat flux sensor with a GLD sticker will
therefore give a better approximation of the heat flux from the espresso machine’s metal
surface than a sensor with a black sticker.

BLK - GLD sticker series manual v2216

25/47

Figure 4.1.1 Measuring with BLK – GLD stickers; application of a BLK black sticker and a GLD
gold sticker on FHF models for measuring radiative and convective heat flux on an espresso
machine. The machine has a polished metal surface of about 45 ˚C. The IR image on the rightshows that the black sticker on the left, as well as the sensor wires and connector blocks, emit
radiation. They appear in red on the image. The gold sticker and the metal surface have lower
emission and appear as “bluish” on the image. Mounted on the same surface, the BLK and GLD
stickers have the same temperature. The measurement with the sensor with the GLD sticker ismost representative of the heat flux at the polished metal surface, while the sensor with the BLK
sticker overestimates the heat flux.
Users could also choose to attribute a theoretical emission to the stainless steel and estimate
the radiation loss using the formula of 3.3:
Φradiative BLK = ΦBLK - Φconvectiive = (UBLK/SBLK) – (UGLD/SGLD)(4.1.1)andΦradiative, stainless steel = (εstainless steel / εBLK ) Φradiative BLK

4.2(4.1.2)

Sources covering part of the sensor field of view; the view
factorIn case a radiating source does not occupy the full field of view, solid angle of 2 Π steradian, ofa flat heat flux sensor, it is possible to express the irradiance received by the sensor in terms ofan optical view factor, fTo calculate the radiative heat flux Φincoming•••

emitted by the source,
incoming at the heat flux sensor locationin the heat flux sensor planeΦincoming = σ∙f∙ε source∙(T source +273)4

BLK - GLD sticker series manual v2216(4.2.1)

26/47

For example, assuming that the sensors can be represented as a point under the source,
for the round infra-red radiator in figure 4.2.1 below, the view factor, f, is determined withf = sin(θ)2(4.2.2)

Figure 4.2.1 measuring radiative heat flux of a round source. The sensor is situated on a heatsink at Tsensor. The source does not fully occupy the full field of view of the sensors. Radiationfrom the source originates from an angle θ.
Assuming that all emission coefficients are 1, the total incoming heat flux of the radiation fromthe source and ambient origin at the sensors isΦincoming = σ∙f∙(Tsource + 273)4 + σ∙(1 – f)∙(Tambient + 273)4(4.2.3)

The radiative flux measured by a BLK sensor is:Φradiative = ΦBLK - Φconvective GLD = (UBLK/SBLK) – (UGLD/SGLD)(4.2.4)

Φradiative [SOURCE ON] =f∙αBLK,Tsource∙Φradiative, source + (1-f)∙αBLK, Tambient∙Φradiative, ambient - σ∙εBLK, emitted∙(TBLK + 273)4(4.2.5)The heat flux of the source can only be measured by switching the source off, and assume thesource then also returns to ambient temperature:Φradiative [SOURCE OFF] = αBLK, Tambient∙Φradiative, ambient - σ∙εBLK, emitted∙(TBLK + 273)4

BLK - GLD sticker series manual v2216(4.2.6)27/47

Φradiative, incoming, source =(Φradiative [SOURCE ON] - Φradiative [SOURCE OFF] + f∙αBLK, Tambient∙Φradiative, ambient)/αBLK, Tsource(4.2.7)

In case f is sufficiently small, indicating that only a small portion of the ambient space is shadedby the source, or in case the radiative flux from ambient sources to the sensor is small because
TBLK is close to Tambient, the term f∙εBLK, Tambient∙Φradiative, ambient may be ignored. ThenΦradiative, incoming, source =(Φradiative [SOURCE ON] - Φradiative [SOURCE OFF])/αBLK, Tsource

4.3(4.2.8)Heat flux measurement to characterise ovens, thermal
profiling

4.3.1 General principles
Heat flux sensors are frequently applied to characterise ovens, for example in the baking
industry or in ovens used for production and curing of rubber insulation foams. In suchapplications a BLK and a GLD sensor and a thermally insulated datalogger are placed on
the conveyor belt in the oven. They move through the oven at a speed representative of
the normal production process, sometimes along with the product.
This process of characterisation is called Thermal Profiling, TP.
The purposes of TP may be:•••

characterisation of the heat transfer in the ovenquantifying and separating the effects of heating by air and heating by radiation
establishing a fingerprint or reference thermal profile, not aiming at accurate heattransfer measurement. This fingerprint can later be used as a baseline. This is usefulwhen servicing ovens, when trying to copy oven settings from one oven to another,for fault-finding, and to compare to similar processes elsewhere.

The parameters typically measured are:••••air temperature, [Tair]sensor body temperature [Tsen]
total heat flux (BLK sensor)] [Φ total]
convective heat flux (GLD sensor) [Φ convective]

Derived parameters are:•air temperature

BLK - GLD sticker series manual v2216

28/47

•
•

local air speed, expressed as the heat transfer coefficient [Ctr ] (characterising heatingby air)local equivalent blackbody temperature, or incoming radiative heat flux
(characterising heating by radiation) [Tblackbody]

In some cases, it is sufficient for comparative purposes only, to establish a fingerprint
using only a single BLK sensor. In that case the purpose is:•establish a total heat flux profile (radiative + convective) with a “reference sensor”.

To produce reproducible results, it is beneficial if:••

the reference sensor has a standardised geometry and heat capacity
measurement is started at a standardised sensor body temperature

Points of attention in the TP measurement are:
•

•

•

•

•

•

•
•

be careful with ambient air temperature measurements; temperature sensors mayheat up by radiation. In that case they no longer measure the true ambient air
temperature. We recommend shielding the ambient air temperatures from radiation,or using gold plated ambient air temperature sensors
be careful to avoid condensation of fluids (water vapour) on the heat flux sensor.
Heat the sensor to above any local dew point (in the oven) before starting themeasurement. Condensation may be recognised by sudden increase of heat flux inhigh-humidity area, followed by decreasing flux when the fluid evaporates again.
the sensor response time must match that of the process. In case transport belts
move too fast relative to the radiative and convective sources, the sensor may not beable to register details of the process. On the other hand, this may not matter; theheat flux integrated over time in [J/m2] will still be representative.
a heat flux sensor behaves as a simple first order system; it can be described using asingle time constant. The response time of such sensors may mathematically be
improved by a factor 2 (made shorter), in data post-processing.
synchronisation of BLK and GLD sensors may be an issue. Make sure they are
exposed to the same source at the same time or introduce a time lag in postprocessing.
sensors must not overheat. The maximum temperature of the sensor top surface is afunction of the temperature of the heat sink, to which the bottom of the sensor isconnected, plus a temperature difference between bottom and top surface of thesensor generated by the local heat flux. Typical measures to limit overheating arestarting the experiment with a low heat sink temperature, using a heat sink with ahigh heat capacity, thermally insulating the heat sink, or using a heat sink thatreflects radiation. For FHF sensors the maximum rated operating temperature forcontinuous use is 120 ˚C. TP experiments are typically short-term (< 30 min) only
and we may use 150 ˚C as maximum rated temperature.
product may also gain heat from the conveyor belt; in some cases, “belttemperature” is measured as wellusers may try to estimate which part of heat transported to the product is radiative
and which part is convective. Please note that this estimate is qualitative only

BLK - GLD sticker series manual v2216

29/47

because both the convective and the radiative heat flux level and the ratio between
these two depends on the product surface temperature. The heat flux sensor surface
temperature may not be representative.

4.3.2 Equations typically applied in TP experiments with FHF05 series
To determine the main measured quantities Tair, Φincoming, Ctr and the equivalent
blackbody temperature T source, blackbody.
Temperature corrected heat fluxes measured by BLK and GLD sensors:
ΦGLD = UGLD/(SGLD∙(1 + 0.002∙(TGLD – 20)))(4.3.2.1)

ΦBLK = UBLK/(SBLK∙(1 + 0.002∙(TBLK – 20)))(4.3.2.2)

Surface temperatures of BLK and GLD sensors are measured temperatures corrected forheat flux and the thermal resistance of the sensors. Usually, but not always, themeasured temperatures TBLK and TGLD are identical, as they are mounted on the same
metal heat sink.
In case we use FHF series sensors:
TBLK, corrected = TBLK + 12 x 10-4∙ΦBLK(4.3.2.3)

TGLD, corrected = TGLD + 5.5 x 10-4∙ΦGLD(4.3.2.4)

The heat transfer coefficient:
Ctr = ΦGLD/(Tair - TGLD, corrected)(4.3.2.5)

The radiative part Φradiative of the total flux ΦBLK
Φradiative= ΦBLK - Φconvective= UBLK/(SBLK∙(1 + 0.002∙(TBLK – 20))) – Ctr∙(Tair – TBLK, corrected)(4.3.2.6)

In case the sensor remains at relatively low temperature and the source is an infra-redlamp,-40 ˚C < TBLK < 70 ˚C,
300 ˚C < Tsource < 600 ˚C(4.3.2.7)(4.3.2.8)

We then assume:
εBLK, emitted = 0.89

(4.3.2.9)

αBLK, incoming = 0.95

(4.3.2.10)

BLK - GLD sticker series manual v2216

30/47

The incoming radiative flux:
Φincoming = 1.05∙Φradiative +0.94∙σ∙(TBLK +273)4(4.3.2.11)

Φconvective, incoming may also be calculated, but that parameter is of less use than the Ctr,
because it is valid only for an object with a certain surface temperature Tsurface
Φconvective = Ctr∙(Tair – Tsurface)(4.3.2.12)

Another way to express the incoming radiative flux is the equivalent blackbody
temperature of the radiation source, asumming an emmisivity of ε = 1 of the source:
Tsource, blackbody =((Φradiative + 0.89∙σ∙(TBLK, corrected + 273)4)/(0.95∙σ))1/4 – 273(4.3.2.13)

4.3.3 Warnings in case of sensor overheating
To warn for overheating we monitor the highest temperature, which is the surface
temperature of the BLK sensor. In case of sensors of the FHF series:
TBLK, corrected = TBLK + 12 x 10-4∙ΦBLK(4.3.3.1)

TBLK, corrected < 120 ˚C(4.3.3.2)

BLK - GLD sticker series manual v2216

31/47

5

Specifications of BLK – GLD sticker series

5.1

Specifications of BLK – GLD stickers

BLK – GLD sticker series can be applied to a heat flux sensor. BLK stickers provide thesensor with a black absorbing surface so that it measures convective and radiative heat
flux, in W/m². GLD stickers provide the sensor with a gold reflecting surface so that it
measures convective heat flux only. Combining BLK and GLD stickers, applied to two
separate heat flux sensors, allows for measurement of radiative heat flux.
Table 5.1.1 Specifications of BLK – GLD sticker series (continued next page)
BLK SPECIFICATIONS
Product typeMeasurand
Measurand in SI units
Measurement range
Measurement function / required
programming
Rated temperature range - continuous
use
Rated temperature range - shortintervals
Spectral range (UV-VIS-NIR-FIR)
Absorption over range
Carrier material
Coating material
Adhesive
Sticker thickness
Sticker thermal resistance
Sticker thermal conductivity
GLD SPECIFICATIONS
Product typeMeasurand
Measurand in SI units
Measurement range
Measurement function / required
programming
Rated temperature range – continuous
use
Rated temperature range – shortintervals
Spectral range (NIR-FIR)
Reflection over range
Spectral range (VIS)
Reflection over range
Solar absorption
Carrier material
Coating material-

stickerconvective + radiative heat flux
heat flux density in W/m²(-2 to 2) x 10³ W/m²
(HFP01)(-10 to 10) x 10³ W/m² (FHF05 series)
Φconvective+radiative = U/S-40 to +150 °C-40 to +260 °C
250 to > 10000 × 10-9 m> 95 %
see appendix for more information
Polyimide (Kapton®)fully inorganic metal-based
3M™ VHB™ F9460PC acrylic transfer tape
0.14 x 10-3 m
10 x 10-4 K/(W/m2)
1.38 x 10-1 W/(m·K)
stickerconvective heat flux
heat flux density in W/m²(-2 to 2) x 10³ W/m²
(HFP01)(-10 to 10) x 10³ W/m² (FHF05 series)
Φconvective = U/S-185 to +150 °C-185 to +260 °C
700 to > 10000 × 10-9 m> 95 %
see appendix for more information
400 to 700 × 10-9 m> 80 %
see appendix for more information< 20 %
Polyimide (Kapton®)gold

BLK - GLD sticker series manual v2216

32/47

Table 5.1.1 Specifications of BLK – GLD sticker series (started on previous page,
continued next page)
Adhesive
Sticker thickness
Sticker thermal resistance
Sticker thermal conductivity
GENERAL SPECIFICATIONS

ARcare® 8026 silicone transfer tape
0.05 x 10-3 m
3.5 x 10-4 K/(W/m2)
1.45 x 10-1 W/(m·K)

Effect on sensor sensitivity
Effect on type T sensor (FHF sensors only)
Additional response time (95 %)Rated temperature range when applied
to sensor
Sticker dimensions
BLK-10X10 / GLD-10X10
BLK-15X30 / GLD-15X30
BLK-50X50 / GLD-50X50
BLK-15X85 / GLD-15X85
BLK-85X85 / GLD-85X85
BLK-80 / GLD-80
Bending radius
Protection foil
INSTALLATION AND USE

negligible
negligible
3 s (nominal)
see sensor specifications

Typical conditions of use

in experiments, in measurements in laboratory andindustrial environments. Exposed to heat fluxes forperiods of several minutes to several years. Sensor
connected to user-supplied data acquisition
equipment. Regular inspection of the sensor andsticker surface. Continuous monitoring of sensor
temperature. No special requirements for immunity,
emission, chemical resistance.
see recommendations in this user manual
Sticker surfaces should be kept clean
General cleaning: do not use any solvents, gently
wipe with optical microfibre cloth and if neededdemineralised water.

Recommended maintenanceApplication of stickers on sensor

Installation of sensors

MEASUREMENT ACCURACY
Uncertainty of the sensor
Uncertainty of the measurement(10 x 10) x 10-3 m(15 x 30) x 10-3 m(50 x 50) x 10-3 m(15 x 85) x 10-3 m(85 x 85) x 10-3 m
Ø 80 x 10-3 m
see sensor specifications for limiting bending radiusremove before measurement

FHF: apply on side without dot
HFP: apply on side coloured red
sensors are applied so that incoming heat flux on thatside produces a positive heat flux signal.
see recommendations in this user manual
see instruction sheet included with delivery
see our instruction video on YouTube,or order sensors with stickers pre-applied at the factory
Preferably install sensors with BLK and GLD on thesame heat sinksee recommendations in the sensor manuals
see recommendations in this user manual
Users should make their own uncertainty evaluation
see user manual of the sensor for more information
about calibration method and uncertainties
Users should make their own uncertainty evaluation
statements about the overall measurement
uncertainty can only be made on an individual basis

BLK - GLD sticker series manual v2216

33/47

Table 5.1.1 Specifications of BLK – GLD sticker series (started on previous pages)
VERSIONS AND ORDER CODES
BLK-10X10 / GLD-10X10
BLK-15X30 / GLD-15X30
BLK-50X50 / GLD-50X50
BLK-15X85 / GLD-15X85
BLK-85X85 / GLD-85X85
BLK-80 / GLD-80
OPTIONS

to be used with model FHF05-10X10
to be used with model FHF05-15X30
to be used with model FHF05-50X50
to be used with model FHF05-15X85
to be used with model FHF05-85X85
to be used with HFP01 heat flux sensor

Pre-applied to the sensor

When opting for pre-application of the sticker to thesensor at the factory, please use the following
ordering code:
product code sensor with wire / cable length indicated+ product code sticker
example: HFP01-05-GLD-80
for an HFP01 with 5 metres of cable and a pre-applied
gold sticker

5.2

Dimensions of BLK – GLD stickers

50

15
50

10

30
10

15

85

85

Ø 80

85

BLK sticker thickness = 0.14 mm
GLD sticker thickness = 0.05 mm

Figure 5.2.1 Dimensions of BLK – GLD sticker series; all dimensions in x 10-3 m for both
BLK and GLD sticker. Top row from left to right: -10X10, -15X30, -50X50. Bottom row
from left to right: -15X85, -85X85 and -80. All BLK stickers have a thickness of 0.14 mm,
GLD stickers have a thickness of 0.05 mm.

BLK - GLD sticker series manual v2216

34/47

Figure 5.2.2 The dimensions of the BLK – GLD stickers match the dimensions of thecorresponding heat flux sensors FHF05 series and HFP01

1

Figure 5.2.3 Layer build-up for the BLK - GLD sticker series. Depicted is BLK/GLD50X50
(1)
(2)
(3)

protective foil
BLK / GLD sticker
release liner with peeling tab

BLK - GLD sticker series manual v2216

35/47

6

Installation of BLK – GLD sticker series

6.1

Application procedure

For the best possible measurement of heat flux sensors with BLK - GLD stickers applied,
it is important that the application is done correctly. The stickers must be aligned withthe sensor, without leaving scratches, (finger) grease, or inclusion of air pockets.
It is advised to do a quick instrument check of the sensor, before applying the sticker.
See the user manual of the sensor for further instructions.
NOTICE
Wear powderless gloves during application.
NOTICE
BLK – GLD stickers are designed for one-time application. Removing stickers
after application will make them permanently unsuitable for use.
NOTICEDo a quick functional check of sensor performance before application of the
sticker.

• When applying a BLK black or GLD gold sticker to FHF05(SC), please note it should beapplied to the side of the heat flux sensor where the dot on the foil is NOT visible.
• When applying a BLK black or GLD gold sticker to HFP01, please note it should beapplied to the side of the heat flux sensor which is coloured red.

Table 6.1.1 Application procedure for BLK – GLD stickers (continued next page)
1

Place the sensor on a stablesurface as shown on the right.
Make sure the correct side isfacing upward.
Before applying the sticker,
clean the sensor surface using
alcohol (IPA) wipe provided withthe sticker.

BLK - GLD sticker series manual v2216

36/47

2

Partially peel and cut the releaseliner (approximately 1 cm). Do
not remove the release liner
completely.

3

Position the sticker onto thesensor surface without applying
force to the top part of the
sticker. If the sticker does notalign properly, carefully remove
the sticker and try again.

release liner
removedrelease liner
still attached4

Once the sensor and sticker are
well aligned, fixate the top partof the sticker. Make sure no air
bubbles are enclosed. Do notremove the sticker after fixating
it as it might damage thecoating of the sticker.

5

Slowly peel off the remaining
release liner while
simultaneously applying the restof the sticker. Again, avoid
including air pockets.

6

Remove the protective foil
before measuring. Handle withcare once the protective foil isremoved.

BLK - GLD sticker series manual v2216

37/47

6.2

Site selection and sensor installation

Table 6.2.1 Recommendations for installation of sensors with BLK – GLD stickers
Locationchoose a location that is representative of the process that is analysed
avoid direct exposure to the sun

Positioning

when using multiple sensors with BLK and GLD stickers, place them side
by side on the same heat sink (a metal plate) so that they haveapproximately the same temperature

Surface cleaning andlevellingcreate a clean and smooth surface before mounting the sensor

Mounting: orientation

when mounting a sensor with a BLK or GLD sticker, keep the directional
sensitivity in mindorient the sensor surface with sticker away from the object on which it ismountedMounting: avoiding
strain on sensor cableor wiresduring installation as well as operation, the user should provide proper
strain relief of the sensor cable/wires so that they are not exposed tosignificant force
first install the cable/wires including strain relief and after that install the
sensorMounting:
curved surfaces

when mounting sensors on curved surfaces, apply BLK – GLD stickers
before mounting the sensor. See the user manual of the sensor for its
rated bending radius

Short term
installation

avoid any air gaps between sensor 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). An air gap of 0.1 x 10-3 m increases
the effective thermal resistance of the sensor by 200 %to avoid air gaps, we recommend thermal paste or glycerol for short term
installation. When mounting on curved surfaces, glycerol is notrecommended as it will leak out
use tape to attach the sensor on the surface. Tape only over the passive
guard area (the area without thermopile traces)
Provide strain relief to the sensor wires
usually, the cables are provided with an additional strain relief, forexample using a cable tie mount as in Figure 6.2.1

Permanent
installation

for long-term installation, fill up the space between sensor and object
with silicone construction sealant, silicone glue or silicone adhesive thatcan be bought in construction depots
the use of thermal paste for permanent installation is discouraged
because it will dry out over time. Silicone glue is more stable and reliable

Electrical connection

when measuring incoming radiation, connect the sensor as indicated in
the user manual of the sensor. Incoming radiation will then give apositive sensor signal
for measurements of outgoing radiation, switch the [+] and [- ] wires ofthe sensor to change its polarity. Outgoing radiation will then give apositive sensor signal

BLK - GLD sticker series manual v2216

38/47

Figure 6.2.1 Installation of model FHF05-50X50 with BLK sticker using tape to attach
the sensor and FHF05-50X50 connection block serving as strain relief. Extra strain relief
on the wires is provided using cable tie mounts equipped with double-sided adhesive
tape. As also indicated in the sensor manual, tapes for mounting of the sensor should
only cover the passive guard area and not over the sensing area (the latter indicated bya dashed line).

BLK - GLD sticker series manual v2216

39/47

7

Maintenance and trouble shooting

7.1

Recommended maintenance and quality assurance

Hukseflux heat flux sensors with sticker perform reliably when kept clean.
Unreliable sensor output can be detected by scientific judgement, for example by looking
for unreasonably large or small measured values. The preferred way to ensure a reliable
sensor output, is a regular critical inspection of surfaces and review of the measured
data.
Table 7.1.1 Recommended maintenance of BLK – GLD stickers.
MINIMUM RECOMMENDED STICKER MAINTENANCE
1

INTERVALSUBJECTACTION

as required
for theapplication

cleaning

Clean the stickers so that they keep their required reflective
and absorptive properties.
Especially the GLD stickers must be treated with care, the gold
layer thickness is very limited, and it may easily be rubbed
away by friction.
General cleaning: do not use any solvents, gently wipe with
optical microfibre cloth and if needed demineralised water.
GLD stickers only: in case normal cleaning does not work use
alcohol or acetone on a soft cloth.
BLK stickers: do not use any solvents.
In case of damage, users may remove stickers and replacethem by a new sticker.
Sensors may also be sent to Hukseflux to apply a new sticker.

BLK - GLD sticker series manual v2216

40/47

For sensor maintenance: consult the sensor manual. Here are some generalrecommendations.
Table 7.1.2 General recommended maintenance of heat flux sensors. If possible, thedata analysis is done on a daily basis
GENERAL: MINIMUM RECOMMENDED HEAT FLUX SENSOR MAINTENANCE
INTERVALSUBJECTACTION1

1 weekdata analysis

compare measured data to the maximum possible or
maximum expected heater power, to other measurementsfrom other redundant instruments and to data previously
measured under identical circumstances.
Look for any patterns and events that deviate from what isnormal or expected. Compare to acceptance intervals.

2

6 months

inspection

inspect wire quality, inspect mounting, inspect location of
installation,
look for seasonal patterns in measurement data

3

2 years

recalibration

recalibration by comparison to a calibration standard
instrument in the field, see following paragraphs.
recalibration by the sensor manufacturer

4

2 years

lifetime
assessment

judge if the instrument will be reliable for another 2 years, or
if it should be replaced

BLK - GLD sticker series manual v2216

41/47

7.2

Trouble shooting

Table 7.2.1 Trouble shooting for heat flux sensors with BLK – GLD stickers
GeneralInspect the quality of application / installation.
Inspect the sticker surface for any damage or stains like grease or dirt.
Inspect if there are any air pockets between the sticker, sensor and surface.
Check if the sensor wires are properly attached to the data logger.
Check the condition of the wires.

Grease or dirt
on BLK surface

Gently clean with a soft cloth, like an anti-static or microfiber cloth, anddemineralised water. Avoid IPA or acetone as it will remove the black coating.
Wear powderless gloves during cleaning.

Grease or dirt
on GLD surface

Gently clean with a soft cloth, like an anti-static or microfiber cloth, and IPA or
acetone. Avoid touching the sticker surface with anything other than a soft clothas it highly prone to scratching. Wear powderless gloves during cleaning.

The sensor
signal has thewrong polarity

Check if the sticker is applied to the correct side of the sensor. See theapplication steps in table 4.1.1 or the installation movie on our YouTube channel
for more information. Polarity issues may also be solved in post-processing of
data.

Issues withsensor signal

See sensor manuals for help on trouble shooting with the sensor signal. A goodstart is to measure the electrical resistance of the sensor. Close to 1 Ohm
indicates a short-circuit, more than 1 MΩ indicates a wire or sensor failure.

7.3

Calibration and on-site checks

The recommended calibration interval of heat flux sensors is 2 years.
Recalibration of field heat flux sensors with stickers is ideally done by the sensor
manufacturer.
On-site (field) calibration is possible by comparison to a calibration reference sensor.
Usually mounted side by side, alternatively mounted on top of the field sensor.
Hukseflux main recommendations for on-site calibrations are:1) to compare to a calibration reference of the same brand and type as the sensor that isused2) to connect both to the same electronics, so that electronics errors (also offsets) areeliminated3) to mount all sensors on the same platform, so that they have the same bodytemperature4) typical duration of test: > 24 h5) typical heat fluxes used for comparison: > 600 W/m2
6) to correct deviations of more than ± 20 %. Lower deviations may be interpreted as
acceptable and may not necessarily lead to a revised sensitivity
Users may also design their own calibration experiment, for example using a wellcharacterised foil heater.

BLK - GLD sticker series manual v2216

42/47

8

Appendices8.1

Reflection versus wavelength and source temperature

Figures 8.1.1 and 8.1.2 show the reflection of the BLK and GLD stickers as a function of
wavelength of the incoming radiation. Upon request, the data from these graphs are alsoavailable in CSV format.
0.2

BLK reflection factor

0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04

BLK reflection

0.02
0

0

5000

10000

15000

20000

wavelength [nm]Figure 8.1.1 reflection factor of BLK sticker as a function of wavelength of the incoming
radiation
1

GLD reflection factor

0.9
0.8
0.7
0.6
0.5
0.4
GLD reflection

0.3
0.2

0

5000

10000

15000

20000

wavelength [nm]Figure 8.1.2 reflection factor of GLD sticker as a function of wavelength of the incoming
radiation

BLK - GLD sticker series manual v2216

43/47

Usually, the spectral composition of the source is not known exactly. If the source can bereasonably described as a blackbody source of a certain temperature T, an averagereflectance factor can be calculated by integrating the reflectance of the sticker with theblackbody spectrum. This way, the formulas of section 2.3 can be used.
Figures 8.1.3 and 8.1.4 and table 8.1.1 show the average reflection factor for the BLK
and GLD sticker for blackbody sources of different temperatures.

BLK average reflection factor

0.1
0.09
0.08
0.07
0.06
0.05

average reflection
factor BLK

0.04
0.03
0.02
0.01
0

0

1000

2000

3000

4000

5000

6000

blackbody source temperature [K]Figure 8.1.3 average reflection factor of BLK sticker when measuring radiation fromblackbody sources of different temperatures

GLD average reflection factor

1

0.95

0.9

0.85

0.8

0.75

average reflection
factor GLD

0

1000

2000

3000

4000

5000

6000

blackbody source temperature [K]Figure 8.1.4 average reflection factor of GLD sticker when measuring radiation fromblackbody sources of different temperatures

BLK - GLD sticker series manual v2216

44/47

Table 8.1.1 average reflection factors of BLK and GLD for various blackbody source
temperatures
blackbody source
temperature [°C]average reflection
factor BLK

average reflection
factor GLD

-40

0.13

0.99

-30

0.12

0.99

-20

0.12

0.99

-10

0.12

0.99

0

0.12

0.99

10

0.11

0.99

20

0.11

0.99

30

0.11

0.99

40

0.11

0.99

50

0.10

0.99

60

0.10

0.99

70

0.10

0.99

80

0.10

0.99

90

0.09

0.99

100

0.09

0.99

150

0.08

0.99

200

0.07

0.99

250

0.07

0.99

300

0.06

0.99

350

0.06

0.99

400

0.05

0.99

450

0.05

0.99

500

0.05

0.99

600

0.05

0.99

700

0.04

0.99

800

0.04

0.99

900

0.04

0.99

1000

0.04

0.99

1500

0.04

0.99

2000

0.03

0.98

2500

0.03

0.97

3000

0.03

0.96

3500

0.02

0.93

4000

0.02

0.90

4500

0.02

0.87

5000

0.02

0.83

5500

0.02

0.80

BLK - GLD sticker series manual v2216

45/47

8.2

EU declaration of conformity

We,

Hukseflux Thermal Sensors B.V., Delftechpark 31, Delft,
The Netherlands

hereby declare under our sole responsibility that:
Product model
Product type

BLK GLD sticker series, all models*
Stickers

is in conformity with the following directives:
2011/65/EU

The Restriction of Hazardous Substances Directive

This conformity is declared using the relevant sections and requirements of the following
standards:
Hazardous substances

RoHS 2 and 215/863 amendment

Eric HOEKSEMA
Director
Delft
June 30, 2022
* NOTE: these are passive components. When implemented in a system, this system should be subjected to independent
conformity assessment.

BLK - GLD sticker series manual v2216

46/47

© 2022, Hukseflux Thermal Sensors B.V.
www.hukseflux.com
Hukseflux Thermal Sensors B.V. reserves the right to change specifications without notice.