RMT HTX Operating manual Datasheet

Operating Manual
Thermoelectric Heat Flux Sensors
HTX SERIES
2015
Release 1.0
THERMOELECTRIC HEAT FLUX SENSORS
CONTENT
1.
2.
3.
4.
5.
6.
INTRODUCTION
Features
SPECIFICATIONS
Numbering system
QUICK START
3.1 About Heat Sensor HTX series
3.2 Preparations for working
3.3 Sensor testing
3.4 Sensor calibration
3.5 Mounting of the Sensor
3.6 Data acquisition
3.7 How to calculate heat flux
3.8 Sensors service
HEAT FLUX SENSORS INTRODUCTION
4.1 Description of installation
4.2 Sides of the Sensor
FUNCTIONALITY TEST
5.1 Checking of AC Resistance
5.2 Checking of Figure-of-Merit.
5.3 Checking Pt1000 thermistor
5.4 Checking of Sensor behavior
INSTALLATION OF SENSORS
6.1 Mounting substances
Adhesive tape
Thermally conductive paste
Thermally conductive glue
6.2 Removal of the mounting substance
6.3 Mounting methods
At the interface between a solid surface and gas
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OPERATING MANUAL. HTX SERIES
Between two solid materials
7.
DATA ACQUISITION
7.1 Datalogger DX8140
Applicability
7.2 Voltmeter as a read-out device
Applicability
7.3 Ohmmeter as a read-out device of temperature
7.4 Third party read-out device
Applicability
8.
DATA ANALYSIS
8.1 Temperature corrections
Example for calculating
8.2 Heat flux measurements
Example for heat flux measurement
9.
SELF-CALIBRATION PROCEDURE
9.1 Method
9.2 Measurement Scheme
9.3 Equipment
9.4 Example
10. MAINTENANCE OF THE SENSOR
10.1 Removing Sensor from measurement setup
10.2 Cleaning of Sensor
10.3 Storage
11. ADDITIONAL INFORMATION
11.1 Electromagnetic field
11.2 Trouble shooting electrical problem
11.3 Application in temperatures outside of calibration range
11.4 Influence of radiative heat flux
11.5 Use in fluids
12. DEFINITIONS
18
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25
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Page 3 of 36
THERMOELECTRIC HEAT FLUX SENSORS
Edition April 2015
Copyright
All rights reserved.
Reproduction in any manner, in whole or in part is straightly prohibited
without written permission of RMT Ltd.
The information contained in this document is the subject to change
without notice.
Limited Warranty
RMT Ltd. warrants that the Thermoelectric Heat Flux Sensor of HTX Series,
if properly installed and used, will be free of defects in material and
workmanship and will substantially conform to RMT’s publicly available
specification for a period of one (1) year after the date that the
Thermoelectric Heat Flux Sensor of HTX Series was purchased.
If the Thermoelectric Heat Flux Sensor of HTX Series, which is the subject
of this Limited Warranty, fails during the warranty period for the reasons
covered by this Limited Warranty, RMT, at this option, will:
REPAIR the Thermoelectric Heat Flux Sensor of HTX Series; OR REPLACE
the Thermoelectric Heat Flux Sensor of HTX Series with another unit of the
same model.
Trademark Acknowledgments
All trademarks are the property of their respective owners.
RMT Ltd.
46 Warshavskoe shosse, Moscow 115230 Russia
phones: +7-499-678-20-82
fax: +7-499-678-20-83
e-mail: [email protected]
www.rmtltd.ru
Page 4 of 36
OPERATING MANUAL. HTX SERIES
1.
INTRODUCTION
Heat Flux Sensors of HTX series – the series of high sensitive and selfcalibrating Sensors with integrated Pt1000 thermistors.
Features
-
High sensitivity
Miniature Design
Self-calibrating
Integrated thermistor
Miniature FET cable and connector
A range of customized dimensions
The Sensors are developed as a series of a range of sizes (diameters): 12,
14, 16, 20, 25, 30 and 40 mm. Optional dimensions (size and thickness) as
well as customized performance parameters are available on request.
The Sensors were developed for measurement of conductive, convective
and radiation heat fluxes in a wide range of heat flux intensities. The high
sensitivity of the Sensors of the series provides accurate experiments and
data on objects of investigations.
One of the feature of the Sensors is the self-calibration method (patent
pending RU2014145948 dated 17.11.2014). It means possibility to
calibrate precisely the Sensor by measurement of its thermoelectric
performance parameters. It is not necessary to remove it and send to labs.
The calibration procedure is possible with use of RMT Datalogger of the
DX8140 series, specially developed for thermoelectric Heat Flux Sensors,
or by use of RMT Z-meters. The calibration procedure is described in
Chapter 10.
Page 5 of 36
THERMOELECTRIC HEAT FLUX SENSORS
2.
SPECIFICATIONS
Product name
HTD
0405908D12
HTD
0412705D16
HTC
HTC
HTC
04060612612612605D20 08D25 08D30
Thermoelectric
Aluminum, painted black
12
2,4
59
50
0,45
4 500
0,5
16
2,1
127
70
0,35
7 500
1,5
20
3,1
126
100
0,32
5 000
1,6
25
3,4
126
110
0,23
4 500
2,3
30
3,4
126
130
0,18
4 000
2,8
40
3,4
284
265
0,21
4 500
5,5
3,2
2,10E03
18,6
3,1
1,40E03
6,8
6,8
2,00E03
6,2
6,6
2,10E03
4,4
7,2
2,50E03
3,5
6,8
2,30E03
1,8
5,91
0,20
8,03
0,20
7,96
0,20
5,55
0,20
5,55
0,20
12,5
0,20
0,04%
0,03%
0,04%
0,04%
0,05%
0,04%
1
3
1
3
1
3
1
3
1
3
1
3
-40 …
+80
-50 …
+150
19
-40 …
+80
-50 …
+150
41
-40 …
+80
-50 …
+150
91
-40 …
+80
-50 …
+150
204
1)
Detector Type
Surface material
Protection
2)
HTC
0628408D40
IP67
2
Surface dimensions dia., mm
Thickness H, mm
Pellet pairs
2
Sensitivity Se, V/(W/m )
Integral sensitivity Sa, V/W
2
Heat Flux Range Pe, ±W/m
Integral Heat Flux Range Pa,
±W
Thermal Time Constant , s
Thermal Resistance RT,
2
K/(W/m )
Integral Thermal Resistance RT,
K/W
Electrical Resistance ACR, Ohm
3)
Temperature Dependence
dS/dT, %/°C
Linearity with Power dS/dP,
2
±%/(W/m )
Homogeneity dS/dA, ±%
Calibration Accuracy, ±%
Thermistor
Calibration Temperature
Range, °C
Operating Temperature Range,
°C
Max. compressive Force for
clamping, kg
4)
Cable Length L, cm
5)
Connector
Pt1000 (1%, 0,375%/°C)
180
-40 …
+80
-50 …
+150
41
-40 …
+80
-50 …
+150
91
180
180
180
180
FMC 0,5/6-ST-2,54-18211355
180
Notes:
1.
Performance parameters shown in specifications are given for ambient temperature
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OPERATING MANUAL. HTX SERIES
2.
3.
4.
5.
Ta=300 K (27 °C)
Application in water - not more than 1 hour. Maximal temperature 100°C.
Average value at Ta=300 K (27 °C). Detailed temperature dependence is given in table
Sensor is equipped with thin FEP Flat Ribbon Cable, 0.025” Pitch, 32 AWG, 1,8 m. Wire
resistance 0,54 Ohm/m
Cable is ended by miniature connector FMC 0,5/6-ST-2,54-18211355 (Phoenix). The
female part must be - MCV 0,5/6-G-2,54 SMD R44-1821588
Numbering system
The following numbering system was developed to order thermoelectric
Heat Flux Sensors of RMT.
The sensor serial number gives some useful information about design of
the sensors.
H T X - 0 5 9 - 0 8 Х 1 2
Description
Dimensions in mm
Shape:
D - dia. (round sensor)
L - square sensor
Pellet height, mmх10
Number of pellet pairs
Type of thermoelectric
module used:
MC «C»
MD «D»
Sensor type:
HT heat
flux
and
temperature
HF heat flux (without
temperature)
HR radiation heat flux
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THERMOELECTRIC HEAT FLUX SENSORS
3.
QUICK START
3.1 About Heat Sensor HTX series
The Heat Flux Sensors of the HTX series – the series of high sensitive and
self-calibrating Sensors with integrated Pt1000 thermistors. The Sensors
were developed for measurement of conductive, convective and radiation
heat fluxes in a wide range of intensities.
The Sensors have a
round shape. Inside
there is an integrated
miniature
thermoelectric module
and
a
Pt1000
thermistor.
Electric
connections come from
the parts by a miniature
FEP Flat Ribbon Cable
(0.025” Pitch, 32 AWG).
The standard length is
180 cm (6”). The cable
output is ended by a sixpin miniature connector
of the type DFMC 0,5/ 6ST-2,54 (Phoenix).
Both sides of the
Sensors are aluminum covered with black paint stable for working in wet
ambient and even under water.
Internal ambient of the Sensor is potted by a silicon compound of high
temperature stability.
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OPERATING MANUAL. HTX SERIES
3.2 Preparations for working
You need to procure the following for working with the Sensors:
-
Mounting substance (i.e. tape, paste, or glue) to mount the Sensor in
your setup.
-
Read-out device (i.e. RMT DX8140 Datalogger, millivoltmeter,
ohmmeter), or third party read-out device. Note that the read-out
device must have passive input for Sensor and active input for
working with Pt1000 thermistor.
-
Device for Sensor self-calibration procedure. If RMT DX8140
Datalogger is procured, the procedure is available. Otherwise any
model of RMT Z-meters is suitable for that.
3.3 Sensor testing
Before mounting the Sensor must be tested as described in Chapter 6.
3.4 Sensor calibration
If necessary, or required for an application the Sensor can be calibrated by
the self-calibration procedure described in Chapter 10.
3.5 Mounting of the Sensor
Ensure that the mounting surface is flat, dry, and free of dust and grease.
Clean the Sensor surface with ethanol or isopropanol. Do not use acids or
alkali for cleaning the Sensor. Mount the Sensor using a mounting
substance. A detailed description of the Sensor mounting is given in
Chapter 6.
The common mounting scheme is advised in Fig. 4.1
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THERMOELECTRIC HEAT FLUX SENSORS
Fig 4.1 Schematic diagram of mounting and functionality of a
HTX Heat Flux Sensor.
3.6 Data acquisition
Connect the Sensor to the read-out devices and collect data according to
the data acquisition procedure.
3.7 How to calculate heat flux
Every Heat Flux Sensor has performance parameter – sensitivity to heat
flux (Sa and Se). The data acquisition device collects voltage output from
the Sensor U.
The heat flux P must be calculated as
𝑃=
𝑈
𝑆𝑖 × 𝐹(𝑇)
(4.1)
Where Si – sensitivity: if Si=Se, P will be outputted in the units of heat
flux density [W/m2]; if Si=Sa, the integral heat flux will be obtained in
[W]; F(T) – temperature correction factor, dependence of sensitivity
on working temperature T.
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OPERATING MANUAL. HTX SERIES
3.8 Sensors service
The service procedures and procedures of removing the Sensors from the
setup are described in Chapter 11.
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THERMOELECTRIC HEAT FLUX SENSORS
4.
HEAT FLUX SENSORS INTRODUCTION
4.1 Description of installation
The Sensor has two flat sides marked differently and also the cable has
marking (red strip – wire #1).
One side of the Sensor is marked by “+” – positive side.
If the Sensor is placed with its positive side to the heat flux (Fig. 5.1), the
positive voltage output will be on the Sensor’s wire #4.
In other words if the positive voltage is on Connector pin #4, the heat flux
comes from the positive side. And vice versa.
Fig. 5.1 Direction of heat flux.
4.2 Sides of the Sensor
Although the positive side is marked differently, the Sensor can work bidirectionally with the same performance. Only the direction of the output
voltage will give information about the direction of the heat flux.
But in the application it is simple to follow the rule – heat comes to the
positive side.
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OPERATING MANUAL. HTX SERIES
5.
FUNCTIONALITY TEST
All the HTX thermoelectric Heat Flux Sensors adhere to high manufacturing
standards. Before shipping, the performance of each Heat Flux Sensor is
individually checked and calibrated. All the data are advised in
Specifications of the Sensor.
However, external factors (e.g. transportation, prior use), may affect the
functionality of the Sensor module. Before the permanent installation, the
Sensor functionality must be tested.
5.1 Checking of AC Resistance
The electrical resistance testing is done using a standard multimeter via a
four-wire probe measurement. The resistance measurement must be done
without any applied temperature gradient (e.g. with the Sensor hanging in
air holding it at the cables).
The resistance must be in the range specified in the Sensor’s respective
datasheet. This value does not include the resistance of the cables.
Resistance below 0.1 ohm indicates a short circuit, while resistance higher
than the value stated in the datasheet indicates physical wearout of the
Sensor and/or its cables. In both cases, the Sensor is not functional and
must be replaced.
5.2 Checking of Figure-of-Merit.
The Sensor is a thermoelectric module device. Performance and
functionality of the Sensor can be examined by two parameters: the AC
Resistance (see above) and Figure-of-Merit. In some cases functionality
checking only by AC resistance measurements is not enough. Particularly in
the case of probable failure, and necessity to investigate reasons of this.
Checking of Z together with ACR gives much more information about
functionality of the thermoelectric Sensor.
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THERMOELECTRIC HEAT FLUX SENSORS
Checking of the Figure-of-Merit requires a special device – Z-Meter.
DX8140 Datalogger. It has a special function of Figure-of-Merit checking.
Contact RMT for the devices and checking. And visit RMT website for more
literature on checking of Figure-of-Merit of thermoelectric modules http://rmtltd.ru/technology/publications/.
The specification of every Sensor contains Z measured at vendor factory
before shipment.
5.3 Checking Pt1000 thermistor
Electrical resistance testing is done using a standard multimeter via a twowire probe resistance measurement.
The resistance must be in the range specified in the Sensor’s respective
datasheet. These values include the resistance of cables. Resistance below
0.5 ohm indicates a short circuit, while a resistance higher than the value
stated in the datasheet indicates physical wearout of the Sensor and/or its
cables. In both cases, the Pt1000 thermistor is not functional.
5.4 Checking of Sensor behavior
Connect the Sensor to a voltmeter (resolution preferably in the 0.1mV
range). Place the Sensor on a metallic surface at room temperature. When
touching the Sensor with a warm finger on the upper surface, you should
get a signal in the mV range.
A Sensor signal below 0.1 mV indicates a short circuit. Check whether the
resistance of the Sensor is > 0.1 ohm as described above.
If the signal randomly fluctuates between a positive and negative signal, or
the voltage is in the +/- 1 V range, you may have an open circuit. Check the
connection of your electrical probes.
If the signal shows one of the three described features above, the Sensor is
not functional and has to be replaced.
In this case, please contact the vendor.
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OPERATING MANUAL. HTX SERIES
6.
INSTALLATION OF SENSORS
6.1 Mounting substances
In order to obtain meaningful measurement data, the HTX Heat Flux
Sensor has to be mounted with adequate mounting substances. Adequate
mounting substances features are high thermal conductivity and low
thickness. Three types of mounting substance are suitable: adhesive tape,
thermally conductive paste, and thermally conductive glue.
The mounting substance should be chosen based on the measurement
setup.
Adhesive tape
Adhesive tape should be used for simple tasks, where quick setup is crucial
and the thermal coupling is of secondary importance.
Clean the surface to be measured and apply the tape to the backside of
the Sensor. Mount the Sensor onto the surface by applying gentle pressure
to establish adhesion. You can add a thermal paste (see the next section)
for improving thermal coupling to the surface.
Thermally conductive paste
Thermally conductive paste is recommended in applications where
pressure is used to fix the HTX Heat Flux Sensor in the measurement setup.
It generates a very strong thermal coupling as the paste adapts to the
surface inhomogeneities.
Clean the surface to be measured and spread a thin layer of paste onto the
backside of the Sensor. Then press the Sensor onto the surface. You may
need to hold the Sensor in place with tape across the electric cables.
Thermally conductive glue
Thermally conductive glue is suitable for applications where additional
mechanical stability is required. Similar to the paste, it generates a strong
thermal coupling and adapts to surface inhomogeneities.
Page 15 of 36
THERMOELECTRIC HEAT FLUX SENSORS
Clean the surface to be measured and spread a thin layer of thermal glue
onto the backside of the Sensor. Then press the Sensor onto the surface
and follow the curing instructions of the glue.
6.2 Removal of the mounting substance
To remove the different mounting substances, refer to the respective
manufacturer’s instruction manual. If no instructions are available, contact
the supplier. Isopropanol and ethanol can be used as cleaning agents
whereas acids and alkali must be avoided to avoid damage to the Sensors.
Rub the surface gently with a soaked tissue to remove residues of the
mounting substance.
6.3 Mounting methods
The Sensor responds to all the three types of heat transfer: conduction,
convection and radiation. The HTX Heat Flux Sensors are fully calibrated
for measuring conductive heat flux. The conductive calibration ensures
highly precise measurements for the following two measurement
scenarios.
At the interface between a solid surface and gas
Fig. 7.1 Mounting onto solid surface.
Page 16 of 36
OPERATING MANUAL. HTX SERIES
Mounting instructions:
1. Select a representative area of the surface you want to study.
2. Ensure that the area of interest is flat, dry, and free of dust and grease.
Clean the Sensor surface with ethanol or isopropanol. Do not use acids or
alkali for cleaning the Sensor.
3. Apply the Sensor using any of the above described mounting substances.
When mounting the Sensor, make sure no air is trapped between the
surface and the Sensor. Air gaps are thermally insulating and heavily
distort the measurement results.
4. Mount the Sensor with the positive side of the Sensor in the direction of
the expected positive heat flux (as described in Section 5.1).
Do not apply more than 200 N per cm2 of compressive force to the Sensor
at any time.
5. In order to ensure meaningful results, we recommend making the
exposed Sensor surface similar to the finish of the surface to be measured.
For example, if the surface to be measured is covered with white paint, you
will get maximum accuracy by painting the Sensor surface with the same
paint.
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THERMOELECTRIC HEAT FLUX SENSORS
Between two solid materials
Fig. 7.2 Mounting between two solid materials.
Mounting instructions:
1. Ensure that both solid bodies have contact areas at least as large as the
HTX Heat Flux Sensor.
2. Ensure that the two solid planes are perfectly parallel to each other and
that the contact surfaces are flat, dry and free of dust and grease. Clean
the Sensor surface with ethanol or isopropanol. Do not use acids or alkali
for cleaning the Sensor.
3. Mount the Sensor with the positive side of the Sensor in the direction of
the expected positive heat flux.
4. Sandwich the Sensor between the two contact areas using any of the
above described mounting substances. It is highly recommended to use
thermally conductive paste or glue to increase the quality of the thermal
contacts between the surfaces and the Sensor.
Do not use too much thermal paste or glue as it increases the risk of
thermal short-cuts between the two contact surfaces. Furthermore, ensure
Page 18 of 36
OPERATING MANUAL. HTX SERIES
that no air is trapped between the surface and the Sensor. Air gaps are
thermally insulating and heavily distort measurement results.
5. A clamping force of 10N - 100N per cm2 is recommended in order to
optimize the thermal contact. The maximal value of 200N per cm2 should
not be exceeded at any time.
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THERMOELECTRIC HEAT FLUX SENSORS
7.
DATA ACQUISITION
The HTX Heat Flux Sensors’ output is an analog voltage signal. Depending
on the measurement task, the voltage signal can be in the μV to mV range.
To read-out the Sensor signal, three options are available: the DX8140
Datalogger, a voltmeter, or a third party read-out device. The following
section describes each option separately.
7.1 Datalogger DX8140
The DX8140 Datalogger is specifically developed for reliable and
straightforward heat flux measurements in combination with the HTX and
HFX Heat Flux Sensors. The DX8140 Datalogger works as a complete
solution with included software. The DX8140 Datalogger can be set to
measure either an analog voltage signal (in V) or heat flux signal (in W/m2).
Please follow the Instruction Manual, which is available for the DX8140
Datalogger.
Applicability
The DX8140 Datalogger is compatible with all HTX Heat Flux Sensors with a
plug.
7.2 Voltmeter as a read-out device
Voltmeters are used for simple measurement tasks and/or for Sensor
functionality tests. In order to read the output voltage of the Sensor with
high accuracy, you need a voltmeter with high resolution. The resolution of
the heat flux measurement is limited by the voltmeter resolution and
noise. Table 1 demonstrates the relevance of voltmeter resolution.
The voltmeter resolution is the most critical feature when choosing the
optimal device. Due to the low electrical resistance of the Sensor, there
are no special requirements regarding the input resistance of the
voltmeter.
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OPERATING MANUAL. HTX SERIES
All the HTX Heat Flux Sensors can be used bi-directionally. If the direction
of the heat flux is reversed, the sign of the Sensor voltage output changes
(i.e. from positive to negative). Since the sensitivity of the Sensor does not
depend on the direction of the heat flux, the measurement of the reversed
heat flux has the same accuracy.
Table 8.1: Heat flux resolution of Heat Flux Sensors of HTX series at
different voltmeter resolution (1 mV and 1 V)
Sensor type
HTD04-059-08D12
HTD04-127-05D16
HTC04-126-05D20
HTC06-126-08D25
HTC06-126-08D30
HTC06-284-08D40
Sensitivity,
2
mV/(W/m )
50
70
100
110
130
265
2
Heat flux resolution W/m
Voltmeter
VoltmeterV
1mV
20
0,020
14
0,014
10
0,010
9
0,009
8
0,008
4
0,004
However, on some voltmeters the measurement of negative voltages may
not be possible or may be less accurate than the measurement of positive
voltages. Further information about the positive and negative sides of the
Sensors can be found in Section 4.
Applicability
Voltmeters are compatible with all the HTX Heat Flux Sensors without a
plug.
7.3 Ohmmeter as a read-out device of temperature
The Heat Flux Sensors of the HTX series have integrated Pt thermistors
which measure average temperature.
The thermistor is useful for experiments where it is necessary to measure
temperature simultaneously with heat flux measurements. And the
measured temperature allows making temperature corrections of Sensor
Page 21 of 36
THERMOELECTRIC HEAT FLUX SENSORS
performance parameters which are temperature sensitive. Temperature
dependences of the parameters are given in the Sensor Specifications.
Selecting a suitable Ohmmeter it is necessary to take into account the
following:
-
Operating current of the measurement must be low to prevent selfheating of the Pt1000 thermistor. The self-heating of the
thermistor distorts results of heat flux measurements by the
Sensor.
We recommend using Ohmmeter with operating current less than
10 A.
-
Resolution of the Ohmmeter must be enough for accurate
temperature measurements.
The Pt1000 thermistor has 0.375%/K temperature dependence.
Thus to measure average temperature with accuracy 0.5 °C, you
need Ohmmeter resolution at least 0.1 Ohm.
We recommend using Ohmmeter with resolution of 0.01 Ohm.
7.4 Third party read-out device
A data logger is highly recommended for the measurement of timedependent variations of the Sensor signal. For the choice of a suitable
device, apply the same considerations as for the voltmeter.
Applicability
Third party read-out devices are compatible with all the HTX Heat Flux
Sensors without a plug.
Page 22 of 36
OPERATING MANUAL. HTX SERIES
8.
DATA ANALYSIS
This section contains the basic analysis methods needed to interpret data
from the HTX and HFX Heat Flux Sensors. All the information necessary for
it can be found in the following documents:
-
Specifications. The Specification is delivered with every Heat Flux
Sensor for R&D Applications. It contains the Sensor sensitivity Se0
[V/(W/m2)] and integral sensitivity Sa0 [V/W] at calibration
“standard” temperature T0, and all correction factors that are
needed to increase accuracy of the results.
-
Datasheet. The datasheet provides an overview for all technical
parameters of HTX Heat Flux Sensor. It also states the Sensor area,
which is necessary for calculating heat flux.
8.1 Temperature corrections
The sensitivity of the thermoelectric Heat Flux Sensors depends on the
temperature at which they are used. For thermoelectric Heat Flux Sensors
of the HTX series averaged temperature dependence of 0.2%/°C is given in
the Specifications and Datasheets (Table 9.1). The standard calibrated
Sensitivity is given in the specification at temperature 300K (27°C) which is
selected as “standard”.
Thus, if using the Sensors at temperatures below or above 300K (27°C),
with every degree of Centigrade accuracy becomes worse by 0.2-0.25% per
degree.
For temperature range close to the “standard” temperature, i.e. +/-1 °C,
the inaccuracy of the measurements in the general case is negligible –
about ±1%.
But for a wider range of temperatures and for precise measurements the
temperature corrections are recommended.
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THERMOELECTRIC HEAT FLUX SENSORS
It is easy to obtain them as for all thermoelectric Heat Flux Sensors of RMT
the temperature dependences are investigated and general formulas are
advised in the Specifications and Datasheets.
The temperature dependence of sensitivity is given as a polynomial of the
3-rd order:
𝑆𝑎 = 𝑆𝑎0 × [(A2 × (𝑇 − 𝑇0 )2 + A1 × (𝑇 − 𝑇0 ) + A0 )]
(9.1)
where 𝐴0 - is always =1; 𝑆𝑎0 - sensitivity at “standard” calibration
temperature 𝑇0 (= 300𝐾); 𝑆𝑎 – sensitivity at working
temperature 𝑇.
In the expression (9.1) value in brackets is a temperature correction factor.
𝐹(𝑇) = [(A2 × (𝑇 − 𝑇0 )2 + A1 × (𝑇 − 𝑇0 ) + A0 )]
(9.2)
Sensitivity Se [mV/(W/m2)] is also given in the Sensor Specification
(Chapter 3. Specifications) and it correlates with the integral sensitivity Sa
[V/W] as
𝑆𝑒 = 𝑆𝑎 × 𝑆
(9.3)
where 𝑆 – sensitive surface of the Heat Flux Sensor.
Thus the temperature correction factor 𝐹(𝑇) is the same for both
sensitivities
𝑆𝑎 = 𝑆𝑎0 × 𝐹(𝑇)
(9.4)
𝑆𝑒 = 𝑆𝑒0 × 𝐹(𝑇)
(9.5)
The coefficients of the polynomial expression are common and are given in
the Datasheet of the Heat Flux Sensor series (table 2).
Table 9.1. Polynomial expression of temperature dependence of Sensors
sensitivity
Page 24 of 36
OPERATING MANUAL. HTX SERIES
Sensor series
HTX
HFX
HRX
A0
A1
A2
dS/dT, %
1
1,937E-03
-1,634E-05
0,20
1
2,299E-03
-2,094 E-05
0,25
1
2,299E-03
-2,094 E-05
0,25
Temperature range of calibration -40…+80 °С
Common formula
𝑆𝑎 = 𝑆𝑎0 × [(A2 × (𝑇 − 𝑇0 )2 + A1 × (𝑇 − 𝑇0 ) + A0 )]
Ta, K
300
300
300
Thus, to obtain the temperature correction, you need to know average
temperature T of measurement. The Sensors of the HTX series have
atemperature Sensor integrated. You can use a measured value of the
average temperature by the thermistor directly to get temperature
corrections of the Heat Flux Sensor.
If a Heat Flux Sensor without an integrated temperature Sensor is used
(the HFX and HRX series) you need to apply an external temperature
Sensor.
If T is not measured, it can be approximated by the following formula:
𝑇=
𝑇ℎ + 𝑇𝑐
2
(9.6)
where Th and Tc are the respective temperatures of the hot and the
cold sides of the Sensor.
Typically, the difference between Th and Tc is small. If the Sensor is
mounted onto the hot surface, T is better approximated by T = Th.
Example for calculating
The Sensor type HTD04-126-05D20 was taken for measurements.
The Sensor is mounted on a warm surface and is exposed to air. The
surface has a temperature of 50°C, which is a good approximation for T
(see the last section).
The following Sensor parameters are given in its specification (Chapter 3.
Specifications):
Page 25 of 36
THERMOELECTRIC HEAT FLUX SENSORS
Se = 100 μV/(W/m2)
Sa = 0.32 V/W
dS/dT=0.2%/°C
To = 27°C
The temperature correction factors are the following:
-
With use of averaged dS/dT (=0.2%/°C)
𝐹(𝑇) = 1 +
-
∂S
× (𝑇 − 𝑇0 ) = 1 + 0.2 × (50 − 27) = 1 + 4.6%
∂T
= 1,046
(9.7)
More precise correction by polynomial expression (9.2) with given
coefficients (table 9.1) gives the following:
𝐹(𝑇) = [(A2 × (𝑇 − 𝑇0 )2 + A1 × (𝑇 − 𝑇0 ) + A0 )]
= [−1,634 × 10−5 × 232 + 1,937 × 10−3 × 23
+ 1] = [−0.00864386 + 0.04455 + 1] = 1,036
(9.8)
The polynomial expression gives a more precise correction factor which is
slightly differing from the rough averaged value.
Thus, if possible, we recommend using the Polynomial expression rather
than an averaged value given in the Specification only as a indicator value.
But for rough estimations the averaged value
∂S
∂T
is quite enough.
8.2 Heat flux measurements
The DX8140 Datalogger, a voltmeter, or a third party read-out device
measures and stores (Datalogger) an analog output in voltage units U (V,
mV, V) .
The heat flux P is calculated with use of sensitivity and calculated
correction factor (theabove section) F(T). Depending on the sensitivity
units V/(W/m2) (Se) or V/W (Sa) the density of heat flux W/m2 (Ps) or
total heat flux W (Sa) will be calculated as
Page 26 of 36
OPERATING MANUAL. HTX SERIES
𝑈
𝑆𝑒 × 𝐹(𝑇)
𝑈
𝑃𝑎 =
𝑆𝑎 × 𝐹(𝑇)
𝑃𝑒 =
(9.9)
(9.10)
Example for heat flux measurement
The same Sensor type HTD04-126-05D20 (the above section) at the
temperature 50°C with a given sensitivity and calculated correction factor
(9.6) measures the following:
Voltage U = 570 μV
Heat flux is the following
𝑈
570
=
= 5.5 𝑊/𝑚2
𝑆𝑒 × 𝐹(𝑇) 100 × 1,036
𝑈
570 × 10−6
𝑃𝑎 =
=
= 1.719 × 10−3 𝑊
𝑆𝑎 × 𝐹(𝑇) 0.32 × 1,036
= 1.719 𝑚𝑊
𝑃𝑒 =
(9.11)
(9.12)
Page 27 of 36
THERMOELECTRIC HEAT FLUX SENSORS
9.
SELF-CALIBRATION PROCEDURE
9.1 Method
Sensitivity of thermoelectric Heat Flux Sensor Sa:
𝑆𝑎 =
𝑈
= 𝑁 × 𝑎 × 𝑅𝑇
𝑃𝑎
(10.1)
where U – Sensor signal at total heat flux Pa; N – number of
thermoelement pairs in the Sensor; S – sensitive surface area; RT –
thermal resistance of Sensor ;  – averaged Seebeck coefficient for
pair of n- and p-type thermoelements.
Figure-of Merit Z of thermoelectric Sensor
𝑍=
(𝑁 × 𝑎)2 × 𝑅𝑇
𝐴𝐶𝑅
(10.2)
where ACR – AC resistance of the heat fux Sensor.
The calibration expression with use of Z, ACR and Seebeck coefficient
are the following
𝑆𝑎 =
1
𝑍 × 𝐴𝐶𝑅
𝑎×𝑁
𝑆𝑒 = 𝑆𝑎 × 𝑆 =
S
𝑍 × 𝐴𝐶𝑅
𝑎×𝑁
(10.3)
(10.4)
where S – sensitive surface area.
Thus, according to the formulas (10.3-10.4) the sensitivity calibration of
the thermoelectric Heat Flux Sensor is available with use:
-
Construction parameters of the Sensor: number of pellets pairs N;
and size of sensitive surface S. The parameters are given in
datasheets and Specifications (Chapter 3. Specifications);
Page 28 of 36
OPERATING MANUAL. HTX SERIES
-
Property of thermoelectric material of the Sensor  (Seebeck
coefficient). This parameter measured at standard temperature is
given in the Sensor Specification. Moreover, temperature
dependence of the parameter is also given in Specifications and
datasheets (Table 10.1).
-
Measurement of Figure-of-Merit Z and AC Resistance ACR of the
Sensor. The measurements can be done with use of DX8140
Datalogger or Z-meters of RMT, any model.
That is really a self-calibration method as it does not require any external
heat source. And it can be done at the user setup.
Table 10.1 Averaged (for pair of n- and p-types pellets) Seebeck coefficient
of thermoelectric Sensors
Typical value
a0, мкВ/К
410
A0
A1
A2
A3
T0, K
1
+1,291E-03
-8,647-06
+7,843E-08
Temperature range -40…+80 °С
Common formula
𝛼 𝑇 = 𝛼 𝑇0 × [(A2 × (𝑇 − 𝑇0 )2 + A1 × (𝑇 − 𝑇0 ) + A0 )]
300
9.2 Measurement Scheme
The self-calibration is made by measurement of Figure-of-Merit and ACR
resistance of thermoelectric Heat Flux Sensor by the four-wire method
which is provided by four wires of the FET cable connected to the Sensor.
1
HT
U
I
6
Fig. 10.1 Connection scheme for self-calibration procedure.
Page 29 of 36
THERMOELECTRIC HEAT FLUX SENSORS
9.3 Equipment
Use the series of Z-Meters made by RMT for measurement of Figure-ofMerit and ACR resistance of thermoelectric Heat Flux Sensor. You can also
use the Datalogger DX8140 series developed for the HTX, HFX series of
Heat Flux Sensors.
9.4 Example
Heat Flux Sensor type HDT04-059-08D12 was obtained with Specification
where were listed the following:
Diameter
- 12 mm
Number of pellet pairs - 59
Seebeck coefficient,  - 405 (at 300K), V/K
The measurements of thermoelectric performance parameters according
to the scheme in Fig 10.1 with use of Z-Meter DX4090
(http://rmtltd.ru/products/devices/testers/zmeters/) gives the following:
Figure-of-Merit , Z
- 1.9x10-3, K-1
ACR
- 5.8 Ohm
Both are referred to T0=300K.
According to formulas (10.3) and (10.4)
𝑆𝑎 =
1
1.9 × 10−3 × 5.8
𝑍 × 𝐴𝐶𝑅 =
= 0.461 𝑉/𝑊
𝑎×𝑁
405 × 10−6 × 59
𝑆𝑒 = 𝑆𝑎 × 𝑆 = 0.461 ×
𝜋 × 122 × 10−6
= 52.1 𝜇𝑉/𝑊
4
The calibration results are close to the Sensor standard Specification
(Chapter 2).
Page 30 of 36
OPERATING MANUAL. HTX SERIES
10. MAINTENANCE OF THE SENSOR
10.1 Removing Sensor from measurement setup
If the HTX Heat Flux Sensor has been mounted using a thermally
conductive tape or paste, it can be easily removed without destroying the
Sensor. The thermally conductive tape and thermally conductive paste can
be removed following the instructions given in Section 4.1.
10.2 Cleaning of Sensor
Cleaning is only necessary before mounting the Sensor. Clean the Sensor
surface with ethanol or isopropanol. Once the Sensor is mounted, no
further cleaning is necessary.
10.3 Storage
Store an unused HTX Heat Flux Sensor at ambient temperature in a clean
and dry place. No further care is required.
Page 31 of 36
THERMOELECTRIC HEAT FLUX SENSORS
11. ADDITIONAL INFORMATION
11.1 Electromagnetic field
Due to the very low electrical resistance of the Sensor and the aluminum
coating, the output signal is resistant to electromagnetic interference.
In most cases, no countermeasures are necessary.
If electromagnetic interference is a problem, typical countermeasures (e.g.
shielded cables, grounding) have to be taken.
11.2 Trouble shooting electrical problem
In case of electrical problems, check all the connections and cables. Check
for loose connections and/or short circuits in the leads.
In some cases, corroded cables are the issue. If the problem cannot be
located in the leads/cables, the Sensor may be broken and has to be
replaced.
11.3 Application in temperatures outside of calibration range
The calibration temperature range of the HTX Heat Flux Sensors is stated
in the respective data sheets.
Within this temperature range, RMT guarantees a relative error less than
+/- 3%.
Outside of this range, the relative error may exceed this value.
11.4 Influence of radiative heat flux
Electromagnetic radiation from deep ultraviolet wavelengths to infrared
may interfere with your measurement. To achieve highest precision make
sure to block off this radiation.
Page 32 of 36
OPERATING MANUAL. HTX SERIES
11.5 Use in fluids
The Sensor is hermetically sealed and may be exposed to moisture or clean
neutral water at temperatures less than 100° C for a short time by properly
insulating all electrical parts. However, long term exposure to wet ambient
conditions is not recommended as this may corrode the metallic leads.
Use in other fluids is not recommended.
In any case, do not expose the Sensor to strong acids or alkalis.
Page 33 of 36
THERMOELECTRIC HEAT FLUX SENSORS
12. DEFINITIONS
Value
𝑃𝑒
𝑃𝑎
𝑆𝑒
𝑆𝑎
𝐷∗
NEP
𝑅𝑇
𝛼
𝐴𝐶𝑅
𝑁
∆𝑇
𝑇ℎ
𝑇𝑐
𝐾𝑇
𝑘
𝑠
ℎ
H
AxB

Z

Page 34 of 36
Units
W/m2
W
V/(W/m2)
V/W
cmHz1/2/W
W/Hz1/2
K/W or
K/(W/m2)
V/K
Ohm
K
K
K
W/K
W/mK
mm2
mm
mm
mm2
s
K-1
Name
Heat flux density
Integral (total) heat flux to Sensor
Sensitivity of Heat Flux Sensor
Integral sensitivity
Detectivity
Noise equivalent power
Thermal resistance
Seebeck coefficient
AC resistance of Sensor
Number of pellets (thermoelements) pairs
Operation temperature difference
Hot side temperature
Cold side temperature
Thermal conductance
Thermal conductivity
Cross-section of pellet
Height of pellet
Sensor thickness
Sensor size (or diameter if “Dia”)
Thermal time constant
Thermoelectric Figure-of-Merit
Emissivity of sensitive surface
OPERATING MANUAL. HTX SERIES
Page 35 of 36
THERMOELECTRIC HEAT FLUX SENSORS
RMT Ltd.
46 Warshavskoe shosse, Moscow 115230 Russia
phones: +7-499-678-20-82
fax: +7-499-678-20-83
e-mail: [email protected]
www.rmtltd.ru
Page 36 of 36