Hukseflux

Thermal Sensors

USER MANUALSBG SERIES
Water-cooled heat flux sensors

Copyright by Hukseflux | SBG series manual v2301 | 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.

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Contents
Cautionary statements
List of symbols
1
Introduction
1.1
Ordering SBG series
1.2
Included items
1.3
Quick instrument check2
Instrument principle and theory
2.1
Detailed measurement equation
3
Specifications of SBG series
3.2
Dimensions of SBG01
3.3
Dimensions of SBG03
3.4
Dimensions of SBG04
4
Standards and recommended practices for use
4.1
Heat flux measurement in fire testing: ISO 14934
4.2
SBG04 in cone calorimeter testing: ISO 5660 and ASTM E1354
5
Installation of SBG series
5.1
Installation in fire testing
5.2
Installation in cone calorimeter
5.3
Electrical connection
5.4
Requirements for data acquisition / amplification
5.5
Cooling
5.6
Non-cooled sensors
6
Making a dependable measurement
6.1
Uncertainty evaluation
6.2
Contributions to the uncertainty budget
7
Maintenance and trouble shooting
7.1
Recommended maintenance and quality assurance
7.2
Trouble shooting
7.3
Recoating / repainting of sensor surfaces
8
Appendices8.1
Appendix on cable extension / replacement
8.2
Appendix on calibration hierarchy
8.3
Appendix on typical heat flux ranges
8.4
Appendix on typical SBG series sensitivities
8.5
Appendix on sensor design: Gardon versus Schmidt-Boelter
8.6
EU declaration of conformity

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List of symbols
Quantities

SymbolUnit

Heat flux
Voltage output
Sensitivity

Φ
U
S

W/m²
V
V/(W/m2)

Subscripts
N/A

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1

Introduction

SBG series are water-cooled sensors that measure heat flux. It is mainly used to test
reaction to fire and fire resistance. It is also used as a calibration reference standard fortest equipment for example in cone calorimeters, flammability and smoke chamber tests.
SBG series complies with the requirements of the most common ASTM and ISO standard
test methods.
SBG series measures heat flux in the range of (5 to 200) x 103 W/m2. Equipped with ablack absorber, heat flux sensors of this type are designed for measurement in anenvironment in which heat flux is dominated by radiation. Using an open detector, SBG
series are also sensitive to convective heat flux. This contribution is usually ignored.
Application in environments with lower than 50 x 103 W/m2 irradiance levels or
environments with significant heat transport to the sensor by convection is possible but
requires a careful evaluation of the measurement uncertainty. SBG series thermopile
sensor generates an output voltage proportional to the incoming irradiance.
Using SBG series is easy. It can be connected directly to commonly used data logging
systems. The heat flux, Φ, in W/m2, is calculated by dividing the SBG output, a small
voltage U, by the sensitivity S.
The measurement function of SBG’s is:Φ = U/S(Formula 0.1)

The sensitivity is provided with SBG on its product certificate.
The sensor is water-cooled. There are 3 models within the SBG series: each with adifferent rated measurement range, calibration reference irradiance level, sensitivity andresponse time. Water-cooling is usually provided by tap water.
SBG01 with a standard body is equipped with a flange. SBG03 has a smooth cylinder
body without a flange. SBG04 is mainly used as calibration reference standard for testingwith cone calorimeters. All specifications and dimensions are standardised for use in cone
calorimeters according to ISO 5660 and ASTM E1354 reaction-to-fire tests. The design
includes two water cooling tubes fixed at a 90° angle to the sensor body, with a sensor bodyof a 0.5 inch diameter.
SBG series has a novel sensor design, which combines the benefits of foil technology of
the traditional Gardon gauges with those of the thermopile technology of the traditional
Schmidt-Boelter gauges.
SBG series has several advantages:•••

Robust and serviceable water tubes
scratch resistant absorber coating (reduced absorber height).
safe storage with a practical protection cap.

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Hukseflux provides a traceable calibration. The reference standard at Hukseflux is ofsecondary standard level. It has been calibrated by comparison to the primary standardof the RISE Research Institutes of Sweden AB (formerly known as Statens
Provningsanstalt (SP)).
SBG series sensors as supplied by Hukseflux are calibrated according to ISO 14934-3.
Hukseflux is ISO 9001 certified, but not an accredited measurement laboratory according
to ISO 17025.
NOTICE
Hukseflux performs traceable calibrations and is certified according toISO 9001, but is not an ISO 17025 accredited calibration laboratory.

Figure 1.1 SBG01. Standard cable length is 2 m.

Figure 1.2 SBG01. Protecting the sensing surface is convenient with the practicalprotection cap.

When the manual addresses the SBG series this generally applies to all SBG sensor
models, in the case that individual models deviate this is indicated. It is the user’s own
responsibility to assess whether the information is applicable to their specific model.
The recommended calibration interval of heat flux sensors is before and after use.

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The uncertainty of the measurement with SBG sensors should be determined case bycase. It is a function of:••••heat flux sensor properties
uncertainty of calibration and quality assurance of the local calibration reference
standard
verification of the stability of SBG sensors in day-to-day measurements, before andafter useapplication-related uncertainties, for example caused by the unknown contribution of
convection and the representativeness of the measurement location

The user should make his own uncertainty evaluation, see the appendix on this subject.

Figure 1.3 SBG01 is the sensor of choice for fire testing.

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Figure 1.4 SBG04 is the sensor of choice as calibration reference standard for cone
calorimeter test equipment, but may also be used for other purposes.
See also:•••

SBG01 water-cooled heat flux sensor with a 1 inch body for measurements < 200 x 103
W/m2.
GG01 Gardon gauge water-cooled high heat flux sensor for high heat flux measurementsof 250 to 1000 x 103 W/m2
HFS01 is a high intensity heat flux sensor intended for concentrated solar andflammability testing.

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1.1

Ordering SBG series

The standard configuration of SBG series is with 2 metres cable.
Common options are:•••

SBG01 standard body with flangeo rated measurement range (5, 10, 20, 50, 100, 200) x 103 W/m2
o longer cable (specify total cable length in m)
SBG03 smooth cylindrical body without flangeo rated measurement range (5, 10, 20, 50, 100, 200) x 103 W/m2
o longer cable (specify total cable length in m)o longer cooling tubes 150 x 10-3 m (specify -P150)
SBG04 Ø12.7 mm (0.5 inch) diameter body with water cooling tubes at 90° angle
o rated measurement range 100 x 103 W/m2o cable length 2 m

1.2Included items

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

heat flux sensor SBG version as orderedcable of the length as ordered
product certificate matching the instrument serial number
options as ordered

1.3

Quick instrument check

A quick test of the instrument can be done by connecting it to a multimeter.
1. Check the electrical resistance of the sensor between the black [-] and white [+]wires. Use a multimeter at the 100 Ω range. Measure the sensor resistance first with one
polarity, then reverse the polarity. Take the average value. The typical resistance of thewiring is 0.1 Ω/m. Typical resistance should be the nominal sensor resistance of 25 Ω forplus 1.5 Ω for the total resistance of two wires (back and forth) of each 2 m. Infinite
resistance indicates a broken circuit; zero or a lower than 1 Ω resistance indicates a shortcircuit.
2. Remove the white removable protection cap from the sensor. 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,
for instance by putting a flame from a consumer type gas lighter at a distance of around0.01 m. The signal should read > 2 x 10-3 V now. Do not expose for more than 10 s.
3. Inspect the sensor surface for any damage.
4. Check the sensor serial number against the certificate provided with the sensor.

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2

Instrument principle and theory

The SBG heat flux sensor measures radiation received by a plane surface from a 180°
field of view angle. This quantity, expressed in W/m2, is called irradiance, and informallyalso heat flux. SBG’s are designed to measure high heat fluxes, in the order of 5 x 103
W/m2 and higher. The radiation spectrum of such sources typically extends from 300 to3000 x 10-9 m. By definition a heat flux sensor should cover that spectral range with aspectral selectivity that is as “flat” as possible.
Using an open detector, SBG’s also sensitive to convective heat flux. This contribution isusually ignored.
In an irradiance measurement by definition the response to “beam” radiation varies withthe cosine of the angle of incidence; i.e. it should have full response when the radiation
hits the sensor perpendicularly (normal to the surface, 0° angle of incidence), zero
response when the radiation has 90° angle of incidence, and 50 % of full response at 60°
angle of incidence.
A heat flux sensor should have a so-called “directional response” (older documents
mention “cosine response”) that is as close as possible to the ideal cosine characteristic.
In order to attain the proper directional and spectral characteristics, a heat flux sensor’s
main components are:••a thermal sensor with black coating. It has a flat spectrum covering the 200 to 50000
x 10-9 m range, and has a near-perfect directional response. The coating absorbs allradiation and, at the moment of absorption, converts it to heat. The heat flows
through the internal thermopile sensor to the metal body. The thermopile sensor
generates a voltage output signal that is proportional to the irradiance.
A water-cooled metal body. This body acts as a heat sink.

Figure 2.1 SBG01 showing its metal body, black coating and cable.

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SBG series users typically assume that the measured heat flux is representative of theundisturbed irradiance at the location of the sensor. Users may also apply corrections
based on scientific judgement.
Using SBG series is easy. For readout the user only needs an accurate voltmeter thatworks in the millivolt range. To convert the measured voltage, U, to a heat flux Φ, thevoltage must be divided by the sensitivity S, a constant that is supplied with eachindividual sensor.

2.1

Detailed measurement equation

In more detail, the measurement equation of SBG series isΦ = U/S + σ·(T + 273.15)4(Formula 2.1.1)

In which the first term represents the incoming irradiance, and the second term
represents the irradiance emitted by the sensor. The constant σ is the Stefan-Boltzmann
constant 5.67 x 10-8 W/(m2·K4).
In case the sensor temperature is of the order of 10 °C, the second term is of the orderof 0.45 x 103 W/m2, which is usually considered negligible, so that the measurement
equation 2.1.1 is abbreviated to:Φ = U/S(Formula 0.1)

Measuring with heat flux sensors, errors may be caused by differences between
calibration reference conditions and the conditions during use. The user should analyse
his own experiment and make his own uncertainty evaluation. Comments on the mostcommon error sources can be found in the chapter about uncertainty evaluation.

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3

Specifications of SBG series

SBG series measures the heat flux density through the surface of the sensor. This quantity,
expressed in W/m2, is called heat flux. SBG series are rated for use in environments in which
the heat flux is dominated by radiation at heat flux levels > 5 x 103 W/m2. Working
completely passive, using a thermopile sensor, SBG series thermopile generates a small
output voltage proportional to this flux. Using an open detector, SBG series are also sensitive
to convective heat flux. This contribution is usually ignored. The sensor must be used at aheat flux level as close as possible to its rated measurement range which is equal to its
calibration reference condition. It must be water-cooled or exposed only for a limited timeinterval. SBG series can only be used in combination with a suitable measurement system.
In testing, the sensor must be calibrated and used in accordance with the recommended
practices of ISO and ASTM.
Model SBG04 is a model specifically intended for use in cone calorimeters. Its specifications,when different, are listed in a separate table.

Table 3.1 Specifications of SBG series (continued on next pages).
SBG SPECIFICATIONS
Sensor type
Sensor type according to ISO 14934
Measurand
Measurand in SI units
Heat flux sensor
Sensor technology
Sensing area diameter
Rated measurement ranges SBG01,
SBG03
Limiting measurement range
Output signal
Sensitivity range
Output voltage signal range
Measurement function / required
programming
Optional measurement function /required programming for correction ofsensitivity as a function of instrument
body temperature
Required readout
Rated operating temperature range
SBG01, SBG03
Rated operating pressure range
Temperature dependence
Non-linearity SBG01, SBG03
Black coating emissivity
Spectral range
Full field of view angle

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water-cooled heat flux sensor
total heat flux sensor
heat flux
irradiance in W/m2
thermopile
both Gardon and Schmidt-Boelter
10 x 10-3 m(5, 10, 20, 50, 100 and 200) x 103 W/m2
150 % of rated measurement range
DC voltage
depending on rated measurement range:
0.1 to 0.7 x 10-6 V/(W/m2)> 5 x 10-3 V at rated measurement range
Φ = U/SΦ = U/S + σ·(T + 273.15)4

1 x differential voltage channel or 1 single ended
voltage channel, input resistance > 106 Ω-30 to +80 °C (sensor body and cable gland temperature)-60 to +200 °C (cable temperature)
Sea level ambient air pressure, not suitable for use invacuum
< 0.1 %/°C
< 2 % of rated measurement range> 0.950 to 50 x 10-6 m
180°

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Table 3.1 Specifications of SBG series (started on previous page, continued on the nextpage).
Response times SBG01, SBG03 (63 %)at different rated measurement ranges
5, 10 x 103 W/m2
20, 50 x 103 W/m2
100, 200 x 103 W/m2
Sensor resistance
Required sensor power
Rated operating relative humidity range
Standard cable length SBG01, SBG03
Cable material type SBG01, SBG03
Cable diameter type SBG01, SBG03
IP protection class
Sensor marking
Gross weight including 2 m cable andprotection cap
Net weight including 2 m cable andprotection cap
WATER COOLING
Typical cooling method
Alternative cooling method
Rated exposure time interval
Rated cooling water operating pressure
range
Rated cooling water flow
Rated cooling water temperature range
Use without water cooling SBG01, SBG03
Weight of metal sensor body SBG01,
SBG03
Metal heat capacity
Heat capacity of sensor body SBG01,
SBG03
Outer diameter of metal cooling tubes
SBG01, SBG03
Recommended hose for cooling watersupplyRecommended coupling for hose
Bending of metal cooling water tubes
SGB03

SB G s e ri e s man u al v23 01< 450 x 10-3 s< 250 x 10-3 s< 200 x 10-3 s
25 Ω (nominal)
zero (passive sensor)
0 to 100 % (non-condensing)
2 m (see options)PTFE
3 x 10-3 m
IP10
serial number engraved on sensor body
approx. 0.3 kg
approx. 0.2 kg

tap water at 3 bar supplied through and drained
through a silicone hoseactively cooling water circulator with water pumpinstead of tap water
indefinite when water cooled
0 to 3 bar> 10 l/hr (0.003 l/s),
preferably 30 l/h (0.01 l/s)
10 to 30 °C
SBG01 and SBG03 may be used uncooled at low heat
flux levels or for short time intervals. See the chapter
on uncooled sensors in this manual for directions
0.11 kg
400 J/(kg·K)
44 J/K
4.2 x 10-3 m(3.2 x 10-3 m for SBG03 option -P150)
6 x 10-3 m outer diameter / 3 x 10-3 m inner diametersilicone hose.
type MCD1702 BODY 1/8 inch NPT + MCD4202
INSERT, see the catalogue via www.cpcworldwide.com
cooling water supply tubes are suitable for careful
one-time bending at radius of > 25 x 10-3 m

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Table 3.2 Use of SBG series according to test standards.
USE IN TESTING
Standards governing use of the
instrument

ISO 14934-1: Reaction-to-Fire Tests - use of heat flux
meters general principles
ISO 14934-4: Reaction-to-Fire Tests - guidance on
use of heat flux meters

Suitable for use in test

ISO 5657: Reaction to fire tests - Ignitability ofbuilding products using a radiant heat source
ISO 5658: Reaction to fire tests - Spread of flame
ISO 5660: Reaction to fire tests - Heat release, smoke
production and mass loss rate
ISO 17554 Reaction to fire tests -- Mass loss
measurement
ISO 9705:1993 Fire tests — Full-scale room test forsurface products
ISO 17431:2006 Fire tests - Reduced-scale model box
test
ISO 17385: Reaction to fire test for façades -part 1
and 3
ISO 3008: Fire resistance tests - door and shutter
assemblies
ISO 5659: Plastics — Smoke generation — Part 2:
Determination of optical density by a single-chamber
test
ISO 14696: Reaction-to-fire tests — Determination offire and thermal parameters of materials, products
and assemblies using an intermediate-scalecalorimeter (ICAL)
ISO 13785: Reaction-to-fire tests for façades- part 1
intermediate scale and part 2 large scale
ISO 9239: Reaction to fire tests for floorings — Part 1:
Determination of the burning behaviour using aradiant heat source
FAA FAR PART 25 APPENDIX F PART 3: Test Method to
Determine Flame Penetration Resistance of Cargo
Compartment Liners

Not suitable for use in test

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ASTM E 285: oxyacetylene ablation testing(heat flux is in the order of 800 x 103 W/m2 which isbeyond the rated measurement range)

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Table 3.3 Installation and use of SBG series.
INSTALLATION AND USE
Installation
Cable extension
Recoating
CALIBRATION
Calibration traceability
Standard governing calibration
Product certificate
Calibration method

Calibration laboratory accreditation
Calibration laboratory management
system certification
Calibration hierarchy
Calibration uncertainty
Recommended recalibration interval ofworking standards
Recommended maintenance of
calibration reference standards

Calibration reference conditions
Calibration reference conditions
SBG01, SBG03
5
10
20
50
100
200
Validity of calibration

SB G s e ri e s man u al v23 01

see recommendations in this manual
see chapter on cable extension or order sensors withlonger cable
ISO 14934-4 paragraph 9.1 allows repainting of
sensors, according to manufacturer recommendations.
After repainting, the sensors must be re-calibrated.
to ITS-90
ISO 14934-3: Reaction-to-Fire Tests - calibration ofheat flux meters secondary calibration
included(showing calibration result and traceability)
SBGC secondary calibration method according to ISO
14934-3. The Hukseflux SBGC method follows therecommended practice of ISO 14934-3, however wecalibrate at one heat flux level only. Calibration relies
on a comparison to a secondary standard heat flux
sensor under a radiant heat source as described inchapter 4. The calibration reference has beencharacterised in the range of 0 to 75 x 103 W/m2.
Calibration at higher heat flux levels is done at 100 x
103 W/m2, using linear extrapolation of the sensitivityof the calibration reference.
not accredited
ISO 9001
From SI through international standards and throughan internal mathematical procedure< ± 6.5 % (k = 2)
fire tests may specify the interval of calibration of theworking standard heat flux sensor. We recommend to
calibrate before and after every test.
we recommend that accredited test laboratories follow
the procedures described in ISO 14934-3 Annex D.
They must have 3 calibration reference sensors(secondary standards, calibrated externally against a
primary standard according to ISO 14934-2), used tocalibrate the working standards. One of these should
be designated as "principal". Clause D.14
recommends that every year one of the 3 instruments
is recalibrated against the (external) primary
standard. Calibration against a primary standard may
be done at RISE (Sweden), NIST (USA) or LNE(France)cooling water temperature < 25 °C
Heat flux level5 x 10³ W/m² ± 5 %10 x 10³ W/m² ± 5 %20 x 10³ W/m² ± 5 %50 x 10³ W/m² ± 5 %100 x 10³ W/m² ± 5 %200 x 10³ W/m² ± 5 %based on experience the instrument sensitivity will notchange during storage

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Table 3.3 Installation and use of SBG series (started on previous 4 pages).
MEASUREMENT ACCURACY
Uncertainty of the measurement
standard governing uncertainty
evaluation in tests
VERSIONS / OPTIONS

statements about the overall measurement
uncertainty can only be made on an individual basis.
see the chapter on uncertainty evaluation.
ISO 29473 Fire test - Uncertainty of measurements infire tests

Version SBG01, SBG03 rated
measurement range
Version SBG01, SBG03 longer cable
Version SBG03 longer water cooling
tubes
Order code SBG01, SBG03 version
ACCESSORIES

5, 10, 20, 50, 100, 200 x 103 W/m2

Spare part
Accessory

removable protection cap SBG01
handheld read-out unit LI19
programmed LI19 handheld read-out unit /datalogger, two spare batteries, one USB cable,
software and a transport case

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02, 05, 10, 20, or specify length in m
-P150
SBG0X-rated measurement range-cable length

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Model SBG04 is a model specifically intended for use in cone calorimeters. Its specifications,when different, are listed in this table.
Table 3.4 Specifications specifically of model SBG04
SBG04 SPECIFICATIONSStandardisation
Operational measurement range
Rated measurement range
Limiting measurement range
Rated operating temperature range

Non-linearity
Response time (63 %)Output signal
Cable material
Cable diameter
Gross weight including 2 m cable andprotection cap
Net weight including 2 m cable andprotection cap
WATER COOLING
Use without water cooling
Weight of metal sensor body SBG04
Heat capacity of sensor body
Outer diameter of metal cooling tubes
Recommended fittings for metal coolingtubes
Bending of metal cooling water tubes
SBG04
USE IN TESTING
Suitable for use in test
INSTALLATION AND USE
Installation
CALIBRATION

all specifications and dimensions standardised for use
in cone calorimeters according to ISO 5660 and ASTM
E1354
(10 to 70) x 103 W/m2
(covering use in cone calorimeters)
100 x 103 W/m2
150 x 103 W/m2
-30 to +80 °C (sensor body)-30 to +600 °C (sensor wire tube)-60 to +200 °C (cable temperature, up to +600 °C
after bake out)
< 2 % within operational measurement range< 250 x 10-3 s> 12 x 10-3 V at rated measurement range
Glass fibre with silicone resin
2.9 x 10-3 m
approx. 0.2 kg
approx. 0.1 kg

SBG04 may not be used uncooled
0.023 kg
8.6 J/K
3.2 x 10-3 m (1/8 inch)
type B-200-9 tube fitting 1/8 inch outer diameter, see
the catalogue via www.swagelok.com
cooling water supply tubes are suitable for careful
one-time bending after “tube support ring” at radiusof > 25 x 10-3 m
ISO 5660: Reaction to fire tests - Heat release, smoke
production and mass loss rate
see recommendations in this manual and the ISO
5660 or ASTM E1354 norms

Calibration reference conditions
SBG04
100
VERSIONS / OPTIONSHeat flux level
50 x 10³ W/m² ± 5 %Version SBG04 rated measurement
range
Version SBG04 standard cable length
Order code SBG04 version

100 x 103 W/m2

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2m
SBG04-100-02

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3.2

Dimensions of SBG01

32

Ø 25,4
3

25,4

41,4

Ø4

1

Ø 34,9Ø 43,9Figure 3.2.1 SGB01 heat flux sensor with a smooth body and flange, dimensions in x 10-3 m.
From top to bottom: 3D view, side view, front view(1) thermopile sensor with black coating. diameter sensing area: 10 x 10-3 m(2) water cooling tube. outer diameter tubes: 4.2 x 10-3 m(3) PTFE cable. standard cable length is 2 m.

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3.3

Dimensions of SBG03

Figure 3.3.1 SGB03-010-02-P150 heat flux sensor with a smooth body, side view
dimensions in x 10-3 m.
(1) thermopile sensor with black coating. diameter sensing area: 10 x 10-3 m(2) PTFE cable. standard cable length is 2 m(3) Option -P150 water cooling tube. outer diameter tubes: 3.2 x 10-3 m (1/8”)

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3.4

Dimensions of SBG04

Figure 3.4.1 SGB04 heat flux sensor, dimensions in x 10-3 m. From top to bottom: front
view, top view, side view(1) thermopile sensor with black coating. diameter sensing area: 10 x 10-3 m(2) water cooling tube. outer diameter tubes: 3.2 x 10-3 m (1/8”)(3) sensor wire tube.
(4) Tube support ring. positioning stop for cone calorimeter.
(5) Cable. standard cable length is 2 m.

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4

Standards and recommended practices
for useCalibration and use of heat flux sensors (officially “heat flux meters”) such as SBG series
is subject to standardised practices according to ISO 14934 “Reaction-to-Fire tests calibration of heat flux meters”. The same procedures will be adopted by ASTM. As cone
calorimeter reference sensor, SBG04 is also subject to ISO 5660 “Reaction-to-fire tests— Heat release, smoke production and mass loss rate”. In case the user performs
accredited testing or works in an accredited organisation, the user must comply withthese standards.
NOTICE
When following standard operating practices, users should purchasetheir own copies of the standard. This manual offers general
guidelines for use only.

4.1

Heat flux measurement in fire testing: ISO 14934

The ISO 14934 standard has 4 parts. We recommend users to purchase the latest
version of the standard.
Table 4.1.1 Standards with recommendations for instrument use in fire testing.
STANDARDS FOR HEAT FLUX SENSOR USE IN FIRE TESTINGISO STANDARD

EQUIVALENTASTM STANDARD

ISO 14934 “Reaction-to-Fire tests - calibration of heat flux
meters”
Part 1: general principle
Part 2: primary calibration methods
Part 3: secondary calibration methods
Part 4: guidance on use of heat flux meters

No equivalent ASTM standard

The most important requirements of the standard are:•to have 3 local "secondary standard" calibration reference standards (i.e. sensors
calibrated against a primary standard according to ISO14934-2) for calibration of the"working standards" (i.e. the instruments used for day to day work for calibration oftest equipment). Calibration according to ISO 14934-2 may be done at NIST (USA),
RISE (Sweden) or LNE (France). Of the 3 calibration reference instruments, 2
instruments must be kept unused until unexpected results appear or until the firstcalibration reference standard is sent away for recalibration. A typical expanded
uncertainty of the sensitivity at SP is in the order of 2 to 3 % (k = 2) in a range from
5 to 75 x 103 W/m2.

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•

•
•

to calibrate every 2 years one of the reference standards against a primary standard.
After calibration this instrument is used to verify the uncertainty of the other 2
calibration reference standards. A single reference standard is usually calibrated at
multiple heat flux levels. It can be used as a reference in the same heat flux range,
and by extrapolation also at higher levels.
to use working standards only at an irradiance level close to its calibration reference
condition.
to compare working standards to a local reference standard before every test andpreferably after every test, following the method specified in ISO 14934-3. The
comparison requires a local irradiance source, for example a cone calorimeter.

4.2 SBG04 in cone calorimeter testing: ISO 5660 and ASTM
E1354
The ISO 5660 standard has 4 parts. We recommend users to purchase the latest versionof the standard.
Table 4.1.1 Standards with recommendations for instrument use in cone calorimeter.
STANDARDS FOR HEAT FLUX SENSOR USE IN CONE CALORIMETERISO STANDARD

EQUIVALENTASTM STANDARD

ISO 5660 “Reaction-to-fire tests — Heat release, smoke
production and mass loss rate”
Part 1: Heat release rate (cone calorimeter method)
Part 3: Guidance on measurement
Part 4: Measurement of heat release for determination of
low levels of combustibility
Part 5: Heat release rate (cone calorimeter method) andsmoke production rate (dynamic measurement) under
reduced oxygen atmospheres

ASTM E1354

The most important requirements of the standard are:
•
•
•
•

•

The flux meter shall be positioned at a location equivalent to the centre of thespecimen face during calibration.
The receiving target shall be flat, circular, of approximately 12.5 mm (half inch) indiameter with a durable matt black finish.
At maximum intervals of 100 working hours, check the operating heat flux meter
against the reference heat flux meter.
The calibration of the working heat flux meter shall be checked by comparison with
two instruments of the same type and of similar range held as reference standards
and not used for any other purpose. One of the reference standards shall be fully
calibrated at a standardizing laboratory at yearly intervals.
The flux meter shall always be used with water-cooling.

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5

Installation of SBG series

5.1

Installation in fire testing

Table 5.1.1 Recommendations for installation of heat flux sensors in fire testing.
Standard operating
practices

If the test is carried out in accordance with a standard: look forrecommendations in the standard.

Orientation

The sensor will work in any orientation.

Protection cap

Use the cap during transport and storage. Remove the cap when
installing and during measurements.

Water cooling

Usually tap water is used, supplied and led out through silicone hoses.
See the chapter on cooling.

Electrical connection

The sensor generates a small voltage output signal. No power supply isrequired. Connect the 2 conductors to a data acquisition system. See thechapter on electrical connection.

Signal amplification

See the paragraph on electrical connection.

Mechanical mounting
SBG01

Use the 3 holes in the flange for sensor mounting. Make sure that theobject that is used for mounting the flange remains relatively cool. Heatshould not conduct easily through the flange to the sensor body.

Mechanical mounting
SBG03, SBG04

Use a circular clamp or equivalent to mount the sensor. Make sure thatthe object that is used for mounting remains relatively cool. Heat should
not conduct easily to the sensor body.

Cable mounting

Provide the cable with an additional strain relief.

Added temperature
sensors

To verify the functionality of the water-cooling, you may connect atemperature sensor to the heat flux sensor body.

Heat shielding

Shield the body sensor and cable as much as possible from radiated andconvective heat.

5.2

Installation in cone calorimeter

Table 5.2.1 Recommendations for installation of SBG04 in cone calorimeter.
Standard operating
practices

If the test is carried out in accordance with the ISO 5660 or ASTM E1354
standard: look for recommendations in the standard.

Orientation

The sensor will work in any orientation. Face the sensitive area towards
the cone heater, positioned at a location equivalent to the centre of thespecimen face during calibration.

Protection cap

Use the cap during transport and storage. Remove the cap when
installing and during measurements.

Water cooling

Water-cooling should always be applied. Usually tap water is used,supplied and led out through 1/8” tube fittings with silicone hoses. See
the chapter on cooling.

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Electrical connection

The sensor generates a small voltage output signal. No power supply isrequired. Connect the 2 conductors to the cone calorimeter dataacquisition system. See the chapter on electrical connection.

Signal amplification

See the paragraph on electrical connection.

Mechanical mounting
SBG04

A “Flux meter mount” is usually supplied with the cone calorimeterequipment and clamped onto the water cooling tubes. For recommended
dimensions of the slot in the “Flux meter mount” see figure 5.5.3

Cable mounting

Provide the cable with an additional strain relief.

Heat shielding

Keep the cable away from direct exposure of the cone heater.

Figure 5.2.2 Dimensions for cone calorimeter mounting, sensitive area to cooling tubes
centre 16 mm.

Figure 5.2.3 Suggested slot dimensions for SBG04 cone calorimeter “Flux meter
mount”.

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5.3

Electrical connection

A heat flux sensor should be connected to a measurement system, typically a so-called
datalogger. SBG series are passive sensors that do not need any power.
Cables may act as a source of distortion, by picking up capacitive noise. We recommend
keeping the distance between a datalogger or amplifier and the sensor as short as
possible. For cable extension, see the appendix on this subject.
Table 5.3.1 The electrical connection of SBG series.
WIRE

MEASUREMENT SYSTEM

White

signal [+]voltage input [+]Blacksignal [‒]voltage input [‒] or groundBlankshieldgroundNOTICE
Putting more than 12 Volt across the sensor wiring
can lead to permanent damage to the sensor.

5.4

Requirements for data acquisition / amplification

The selection and programming of dataloggers is the responsibility of the user. Pleasecontact the supplier of the data acquisition and amplification equipment to see if
directions for use with SBG are available. In case a program for similar instruments isavailable, this can be used. All SBG’s can be treated in the same way as other heat flux
sensors and (analogue) thermopile pyranometers.
NOTICEDo not use “open circuit detection” when measuring the sensor output.

Table 5.4.1 Requirements for data acquisition and amplification equipment for SBG
series in the standard configuration.
Capability to measure small voltage
signals

preferably: < 5 x 10-6 V uncertainty
minimum requirement: 20 x 10-6 V uncertainty(valid for the entire expected temperature range of theacquisition / amplification equipment)

Capability for the data logger or thesoftwareto store data, and to perform division by the sensitivity to
calculate the heat flux.
Φ = U/S (Formula 0.1)

Data acquisition input resistance> 1 x 106 Ω

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Open circuit detection(NOTICE)

5.5

open-circuit detection should not be used, unless this is done
separately from the normal measurement by more than 5times the sensor response time and with a small current
only. Thermopile sensors are sensitive to the current that isused during open circuit detection. The current will generate
heat, which is measured and will appear as a temporary
offset.

Cooling

For normal applications in fire research, the standard 3 bar pressure of tap water supply
are sufficient for operating heat flux meters. In case of extremely high fluxes, which are
not relevant to SBG series (above 2500 x 103 W/m2), additional pressure may benecessary. As water has a very high heat capacity, for 1 inch (25.4 x 10-3 m) diameter
sensors a water supply of 30 l/hr or 0.01 l/s is sufficient to carry away all the generated
heat with a temperature rise of less than 10 °C, taking a safety factor of 4. An alternative
possibility is to use a large vessel filled with water or coolers such as supplied by the
Julabo company, such as model F250 recirculating cooler. The Julabo equipment is a
closed-circuit water cooler with a convective heat exchanger.

Figure 5.5.1 Example of an active water cooler with a pump: Julabo F250.

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5.6

Non-cooled sensors

SBG01 and SBG03 may be used non-cooled (so not connected to the water supply).
SBG04 may not be used non-cooled. This can be considered if:
1. the exposure is so short that SBG does not significantly heat-up; typically thisrequirement is fulfilled in case the time is less than 1 second
2. the flux is so low that SBG cannot significantly heat-up; typically this requirement
is fulfilled in case fluxes are < 1 x 103 W/m2. In this case it is relevant to consider
that the measurement will be inaccurate because of the non-linearity andemission of radiation by the sensor itself
3. there is a large additional heat sink (for instance a block of metal or melting
stearin) attached to SBG
In all cases we recommend:
4. to verify that temperature of the sensor body remains below 80 °C. The limit ofmaterials is 150 °C, but the centre of the sensor gets hotter than the body.
5. to minimize the exposed surface area by adding heat shields and insulation
6. to calculate temperature rise before experimenting; the SBG01 weight is around0.11 kg, so it has a heat capacity of 44 J/K (heat capacity of metal is around 400
J/(kg·K)).
7. add as much thermal mass as possible
Example calculation: at a heat flux of 100 x 103 W/m2 and having an exposed surface
area of 0.0005 m2, the incoming energy is 50 W, which results in 1.2 K/s temperaturerise. Starting at 20 °C sensor body temperature, without cooling a measurement timeinterval of 50 s is feasible. The sensor body will then reach 80 °C.

NOTICE
Using SBG04 without water cooling may lead to permanent damage to the sensor.
Using SBG01 and SBG03 without water cooling may lead to permanent damage tothe sensor when the sensor body temperature exceeds 80 °C.

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6

Making a dependable measurement

6.1

Uncertainty evaluation

The measurement uncertainty is a function of:
•
•
•
•

•

calibration uncertainty
differences between reference conditions during calibration and measurement
conditions, for example uncertainty caused by non-linearity
damage during sensor employment
application errors: the measurement conditions and environment in relation to thesensor properties, the influence of the sensor on the measurand, therepresentativeness of the measurement location
convective heat transport

It is not possible to give one figure for heat flux sensor measurement uncertainty.
Statements about the overall measurement uncertainty can only be made on an
individual basis, taking all these factors into account.
Guidelines for uncertainty evaluation:
1) The formal evaluation of uncertainty should be performed in accordance with ISO 98-3
Guide to the Expression of Uncertainty in Measurement, GUM.
2) Uncertainties are entered in measurement equation (equation is usually Formula 0.1:
Φ = U/S), either as an uncertainty in E (non-representativeness, resistance error anddeflection error) in U (voltage readout errors) or in S (non-stability, temperaturedependence, calibration uncertainty).
3) In case of special measurement conditions, typical specification values are chosen.
These should for instance account for environmental conditions (working temperature
range).
4) Among the various sources of uncertainty, some are “correlated”; i.e. present during
the entire measurement process, and not cancelling or converging to zero when
averaged over time; the off-diagonal elements of the covariance matrix are not zero.
Paragraph 5.2 of GUM.
5) Among the various sources of uncertainty, some are “uncorrelated”; cancelling or
converging to zero when averaged over time; the off-diagonal elements of the covariancematrix are zero. Paragraph 5.1 of GUM.

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6.2

Contributions to the uncertainty budget

6.2.1 Calibration uncertainty at Hukseflux
SBG series factory calibration uncertainty under reference conditions is ± 6.5 % with acoverage factor k = 2.
As a user of SBG series, you may attain a similar uncertainty when calibrating against
your local calibration reference standard.

6.2.2 Uncertainty caused by non-linearity
The SBG01 and SBG03 are calibrated at its rated measurement range, however with aminimum of 5 x 103 W/m2 and a maximum at 100 x 103 W/m2, the SBG04 is calibrated at
50 x 103 W/m2. When measuring at a fraction of the rated measurement range, thesensor output ideally varies linearly with the heat flux. The deviation from this ideal
behaviour is captured in the so-called non-linearity. The non-linearity is expressed as apercentage of the rated measurement range. Non-linearity related uncertainty can bequite large, which is why we recommend to employ sensors measuring close to theirrated measurement range.
The non-linearity specification is ± 2 % of the rated measurement range.
For the model SBG01-200 with a rated measurement range of 200 x 103 W/m2,
the ± 2 % contributes 4 x 103 W/m2 to the uncertainty budget. When measuring with thesame sensor at 20 x 103 W/m2, this is an uncertainty contribution of ± 20 %, which isquite large compared to the calibration uncertainty of 6.5 %.
A model SBG01-20 has an uncertainty contribution of only 0.4 x 103 W/m2 or ± 2 % due
to non-linearity at the same heat flux level of 20 x 103 W/m2.
For the SBG04-100 the non-linearity specification is valid over the operational
measurement range of (10 – 70) x 103 W/m2, covering use in cone calorimeters.

6.2.3 Uncertainty caused by convection
The SBG series are not shielded. Convective heat transport, typically by hot gasses, may
act as a source of measurement error. To estimate the associated uncertainty, the user
may design experiments to vary local heat transfer.

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7

Maintenance and trouble shooting

7.1

Recommended maintenance and quality assurance

SBG series are typically located in hostile environments in which the sensor is underconstant threat of being damaged. Unreliable measurement results are detected by veryfrequent recalibration, by visual inspection of the sensor and by scientific judgement, forexample by looking for unreasonably large or small measured values. Preferably themeasurement is done by multiple sensors, which makes it possible to check against othermeasurements.
Table 7.1.1 Recommended maintenance of SBG series.
MINIMUM RECOMMENDED HEAT FLUX SENSOR MAINTENANCE
INTERVALSUBJECTACTION1

before andafter every
test

recalibration

recalibrate against a local calibration reference

2

before andafter every
test

inspection

inspect sensor coating, cable quality, inspect mounting,inspect the water supply tubing

3

after every
test

data review

judge the feasibility of the measurement datacompare to measurements with other sensors, typically heat
flux and temperature measurements

4

after every
test

lifetime
assessment

judge if the instrument will be reliable for another test

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7.2

Trouble shooting

Table 7.2.1 Trouble shooting for SBG series.
GeneralInspect the sensor for any damage.
Inspect if the wires are properly attached to the data logger.
Check the condition of the cable.
Check the datalogger program in particular if the right sensitivity is entered.
Check the electrical resistance of the sensor between the black [-] and white [+]wires. Use a multimeter at the 100 Ω range. Measure the sensor resistance firstwith one polarity, then reverse the polarity. Take the average value. The typicalresistance of the wiring is 0.1 Ω/m. Typical resistance should be the nominal
sensor resistance of 25 Ω for plus 1.5 Ω for the total resistance of two wires (backand forth) of each 2 m. Infinite resistance indicates a broken circuit; zero or alower than 1 Ω resistance indicates a short circuit.

The sensor
does not give
any signal

Remove the white cap from the sensor. Check if the sensor reacts to heat: put themultimeter at its most sensitive range of DC voltage measurement, typically the
100 x 10-3 VDC range or lower. Expose the sensor heat, for instance by putting aflame from a consumer type gas lighter at a distance of around 0.01 m. The signal
should read > 2 x 10-3 V now. Do not expose for more than 10 s.
Check the data acquisition by replacing the sensor with a spare unit.

The sensor
signal isunrealisticallyhigh or low

Check the cable condition looking for cable breaks.
Check the data acquisition by applying a 1 x 10-6 V source to it in the1 x 10-6 V range. Look at the measurement result. Check if it is as expected.
Check the data acquisition by short circuiting the data acquisition input with a
10 Ω resistor. Look at the output. Check if the output is close to 0 W/m2.

The sensor
signal shows
unexpectedvariations

Check the presence of strong sources of electromagnetic radiation (radar, radio).
Check the condition and connection of the shield.
Check the condition of the sensor cable.
Check if the cable is not moving during the measurement.

7.3

Recoating / repainting of sensor surfaces

ISO 14934-4 paragraph 9.1 allows repainting of sensors, according to manufacturer
recommendations.
Hukseflux recommendations are:Repainting is preferably done by the manufacturer. Do-it-yourself repainting is possible
but if that is done all product warranties are cancelled.
Judge by visual inspection if the thermopile sensor is still well attached to the metal
sensor body. If not, the sensor is beyond repair. Verify sensor functionality. This can also
be done with a non-coated sensor (see the chapter of the quick sensor test). The
thermopile is then visible through its orange-coloured plastic cover.
Purchase a matt (not glossy) black paint which is temperature resistant up to 600 °C.
Silicone-based black paints are a good choice. Typically, aerosol spray cans are mosteasy to use, but such paints can also be used purchased in cans. In case a solvent isneeded: typically, acetone is a good solvent for these paints.

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Surface preparation: In case the existing sensor surface coating has small scratches, but
is otherwise in good condition, do not clean, but apply new paint directly to the existing
paint. In case of heavy damage to sensor surface coatings: remove the existing coating,clean with acetone or ethanol. Lightly sand the orange plastic surface. Take care to leave
the thermopile plastic cover intact.
Paint application: the sensor surface is located in a 0.1 x 10-3 m deep locally lower
surface in the SBG series body. Spray some paint in a small cup, use a pipette to apply
the paint. In case a pipette is not available, use a small paint brush.
Curing: most coatings require curing to reach the required temperature specification.
Cure the coating according to the manufacturer recommendation. Be careful not to
expose the sensor to temperatures above 150 °C.
Recalibration: newly coated sensors should be recalibrated. We do not expect significant(> 5 %) changes relative to the original sensitivity.

7.3.1 Hukseflux factory coating process
Hukseflux uses RUST-OLEUM® Hard Hat 7778 Bar-B-Q-Black.
After application the coating is allowed to dry for at least 3 hours at room temperatureand then heated to 150 °C in stages of max. 50 °C/hour. Ideally an oven with a rampfunction is used. Allow to cool for 24 hrs, the coating is now fully cured.

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8

Appendices8.1

Appendix on cable extension / replacement

SBG series are equipped with one cable. Keep the distance between data logger oramplifier and sensor as short as possible. Cables may act as a source of distortion by
picking up capacitive noise. In an electrically “quiet” environment the SBG series cable
may be extended without problem to 100 meters. If done properly, the sensor signal,
although small, will not significantly degrade because the sensor resistance is very low(which results in good immunity to external sources) and because there is no current
flowing (so no resistive losses). Cable and connection specifications are summarised
below.
Table 8.1.1 Preferred specifications for cable extension of SBG01.
Cable

2-wire, shielded, with copper conductor

Extension sealing

make sure any connections are sealed against humidity ingress

Conductor resistance< 0.1 Ω/mOuter diameter

Typically 4 x 10-3 m

Lengthcables should be kept as short as possible, in any case the total cable
length should be less than 100 m

Outer mantle

with the proper temperature specifications. Typically the mantle andcladding are made of PTFE

Connection

either solder the new cable conductors and shield to those of the original
sensor cable, and make a waterproof connection using heat-shrink tubing
with hot-melt adhesive, or use gold plated waterproof connectors. Always
connect the shield

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8.2

Appendix on calibration hierarchy

SBG series factory calibration is traceable from SI through international standards andthrough an internal mathematical procedure. The formal traceability of the generated
heat flux is through a secondary standard calibration reference to the internationaltemperature standard ITS90.
"The Hukseflux SBGC method follows the recommended practice of ISO 14934-3,
however we calibrate at one heat flux level only. Calibration relies on a comparison to asecondary standard heat flux sensor under a radiant heat source as described in chapter
4. The calibration reference has been characterised in the range of 0 to 75 x 103 W/m2.
Calibration at higher heat flux levels is done at 100 x 103 W/m2, using extrapolation of
the sensitivity of the calibration reference.

8.3

Appendix on typical heat flux ranges

Irradiance from blackbody covering 180° full field of view angle.
Table 8.3.1 Irradiated heat flux versus equivalent blackbody source temperature
calculated using Stefan Boltzmann’s law.
x 103 W/m2

equivalent blackbody temperature °C

1

0.4

10

2

20

500

3

60

750

4

150

1000

5

200

1100

6

266

1200

An indication of allowable heat flux levels for personnel and equipment can be foundbelow.
Table 8.3.2 Allowable heat flux levels in industrial environments.
x 103 W/m2

Btu/Hr Ft2

1

Equipment

9.5

3000

2

Human: Run

6.3

2000

3

Human: Walk

4.7

1500

4

Human: Work (static)

1.6

500

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Table 8.3.3 Typical ranges of heat flux levels, from ISO 14934-4.
x 103 W/m2

Comment

1

300

maximum level in a fully developed fire

2

200 to 100

incident heat flux on the wall in a developed fire enclosure

3

about 100

radiation from burning house4

about 30

causing ignition of tree

5

20 to 10

causing ignition of timber

6

about 7 or 8

lowest level for causing ignition of a timber wall under a pilot
flame

7

about 4

lowest level for causing a burn8

about 2.5

highest level for people to endure9

1.5

solar constant, maximum level of solar irradiance

Table 8.3.4 Typical ranges of heat flux levels, from ISO 5569.
x 103 W/m2

Comment

1

300

jet fire peak

2

200

jet fire average and fully developed fire > 10 x 106 W

3

140

premixed blow torches oxyacetylene

4

120 to 145

peak floor values in post flashover room fires

5

115 to 230

peak wall values in post flashover room fires

6

105 to 175

peak ceiling values for post flashover room fires

7

90 to 200

average wall values for post flashover room fire

8

70 to 150

average ceiling values for post flashover room fire

9

50 to 150high ventilation fully developed room fire 5 % to 10 % O2 byvolume10

60 to 120

premixed gas burner

11

40 to 115

on facade 0.8 m to 3.3 m above window at lintel

1240 to 70

low ventilation fully developed fire 1 % to 5 % O2 by volume

13

30 to 40

small (up to 250 mm high) gas diffusion flames

14

25 to 45

flux on wall from vertical wall burning

15

25

flux below vertical spreading wall flame

16

< 25

oxidative pyrolysis fire 5 % to 21 % O2 by volume

17

20 to 40developing fire with 10 % to 15 % O2 by volume

18

20 to 25

heat flux at floor level in flashover fire with ceilingtemperature > 600 °C

19

18 to 20

match flames20

10 to 40

output from waste paper basket fires

21

12 to 22

critical ignition flux of many materials, e.g. polyethylene,
polyacetal, PMMA, wood, hardboard

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8.4

Appendix on typical SBG series sensitivities

Table 8.4.1 Typical sensitivities per model, 2015 production figures, not to be used as
reference.
MODEL SBG – [measurement range]

SENSITIVITY x 10-6 V/(W/m2)

1

SBG01-05 & 10

0.25 to 0.65

2SBG01-20 & 50

0.28 to 0.42

3SBG01-100 & 200

0.10 to 0.20

4SBG04-100

0.12 to 0.23

8.5

Appendix on sensor design: Gardon versus Schmidt-Boelter

The general name for the SBG series type sensor is nowadays “total heat flux meter”:
according to ISO 14934-1 paragraph 3 definition 3.17, and Annex A.2. The so-called
Gardon and Schmidt-Boelter designs (named after their inventors) are also “total heat
flux meters”. From a metrology point of view there is no difference. They all measureheat flux and are traceable to the same reference. The discussion what design to use is
not relevant. New standards in fire testing will probably avoid using the Gardon or
Schmidt-Boelter names.
SBG series actually uses the multiple thermocouple thermopile of the Schmidt-Boelter
model, and the foil technology of the Gardon model. The SBG series combines the best ofboth technologies and is manufactured according to both designs.

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8.6

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

SBG series, all models
heat flux sensor

is in conformity with the following directives:
2011/65/EU, EU 2015/863

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 known as RoHS 3

Eric HOEKSEMA
Director
Delft, 15 November 2022

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© 2023, Hukseflux Thermal Sensors B.V.
www.hukseflux.com
Hukseflux Thermal Sensors B.V. reserves the right to change specifications without notice.