Hukseflux FTN02 User Manual

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USER MANUAL FTN02

Field Thermal Needle System for Thermal
Resistivity / Conductivity Measurement

Hukseflux

Thermal Sensors

FTN02 manual v1717 2/49

Warning statements

The input voltage for charging should not exceed 5 VDC as
it may lead to overheating of the CRU02.

FTN02 is generally operated from its own 3.7 VDC battery.
This low voltage makes FTN02 safe to use in any
environment.

The TP09 needle is sharp and a potential risk to safety of
the operator. When not being used, it is recommended to
have a protective cover over the needle.

Putting more than 5 volt across the TP09 may result in
permanent damage to the sensor.

FTN02 requires a charged battery. With an empty battery,
approximately one hour of charging is required before
measurements can start. 11 hours of charging are preferred.

TP09 is robust but still vulnerable. In case of doubt if it can
penetrate the sample, the sample should be pre-drilled.

When calibrating in glycerol, the user is assumed to be
familiar with the glycerol safety data.

Like most measurement equipment, FTN02 is not suitable
for use in close proximity to high voltage cables when these
are in operation.

FTN02 manual v1717 3/49

Contents

Warning stat e me nts 2
Contents 3
List of symbols 4
Introduction 5
Ordering and checking at delivery 9

Included items 9

1 Theory 10

1.1 General Non-Steady-State Probe Theory 10

1.2 Data analysis in the CRU02 11

1.3 Data review on PC 12

2 FTN02 design considerations 13
3 General Directions for Performing a Measurement 14
4 FTN02 Specifications 15

4.1 Specifications of FTN02 15

5 Arrival of a Ne w FTN02 17

5.1 Preparation before Arrival 17

5.2 Checking upon Arrival 17

6 Quick System Test 18
7 User Guide 20

7.1 Preparation 20

7.2 Cautionary Notes 20

7.3 Performing Measurements 20

7.4 Calibration 21

7.5 Menu Structure 22

7.6 Software 23

8 Data Transfer, Archiving and Review 24

8.1 Connecting CRU02 and PC, downloading data to a PC 24

8.2 Reviewing Data in the Hukseflux CRU02 Manager 25

8.3 Reviewing Data in Excel 29

9 Maintenance and Storage 31
10 Delivery and Spare Parts 32
11 Appendices 33

11.1 Appendix on modelling TP09 behaviour 33

11.2 Appendix on ASTM and IEEE standards 34

11.3 Appendix on insertion of the needle into hard soils 35

11.4 Appendix on typical soil thermal properties 36

11.5 Appendix on glycerol / glycerine 36

11.6 Appendix on electrical connection of TP-CRU02 37

11.7 Appendix on trouble shooting 38

11.8 Appendix on replacement of a TP 38

11.9 Appendix on battery charging 39

11.10 Appendix on downloading new software versions 39

11.11 Appendix on literature references 40

11.12 Glycerol Material Safety Data Sheet (93 / 112 EC) 41

11.13 Internationa l Chemical Safety Card fo r Glycerol 44

11.14 EC Declaration of Conformity 47

FTN02 manual v1717 4/49

List of sy mbols

Quantities Symbol Unit
Thermal diffusivity a m

2

/s
Distance from the heating wire r m
Heating cycle time H s
Thermal conductivity λ W/(m·K)
Time t s
Temperature T K
Differential temperature, or temperature rise ∆T K
Electrical resistance R

e

Ω

Electrical resistance per meter R

em

Ω/m

Thermal resistivity R

th

m·K/W
Diameter D m
Volumetric heat capacity C

v

J/(K·m2)
Density ρ kg/m3
Current I A
Power P W
Power per meter Q W/m

Subscripts

Property of Pt 1000 sensor sen
Property of the heating wire heat
Property of the needle needle
Property, at t = 0, at t = 180, t =h seconds 0, 180, h

FTN02 manual v1717 5/49

Introduction

The FTN02 Field Thermal Needle System allows performing fast, on-site measurements
of the thermal resistivity or conductivity of soils. The sensor is a Non-Steady-State Probe
(NSSP), TP09, which is mounted at the tip of a lance (LN02). The system is operated
using a hand-held Control and Readout Unit (CRU02).

Figure 0.1 Key components of FTN02 system: from left to right thermal properties
sensor TP09, lance LN02 and Control and Readout Unit CRU02.

Figure 0.2 FTN02 system as delivered in its TC01 transport casing

Hukseflux is specialised in NSSP design. Alternative models, for instance for laboratory
use, are available at Hukseflux.

The measurement method is based on the so-called Non-Steady-State Probe (NSSP)
technique, which uses a probe (also called thermal properties sensor or thermal needle)
in which both a heating wire and a temperature sensor are incorporated. The probe is
inserted into the soil. From the response to a heating step the thermal resistivity (or the

FTN02 manual v1717 6/49

inverse value, the conductivity) of the soil can be calculated. The measurement with
FTN02 complies with the IEEE Guide for Soil Thermal Resistivity Measurements
IEEE Standard 442-1981(03) as well as with ASTM D5334-14 Standard Test Method for
Determination of Thermal Conductivity of Soil and S oft Rock. The main application of
FTN02 is route surveying for high voltage electric power cables and for heated pipelines.

In general an NSSP consists of a heating wire, representing a perfect line source, and a
temperature sensor capable of measuring the temperature at this source. The probe is
inserted into the soil that is investigated. The NSSP principle relies on a unique property
of a line source: after a short transient period the temperature rise, ∆T, only depends on
heater power, Q, and medium thermal conductivity, λ:

∆T = (Q / 4 π λ) (ln t + B)

With ∆T in K, Q in W/m, λ in W/(m·K), t the time in s and B a constant. By measuring the
heater power, and tracing the temperature in time (for FT N02 typically during 5
minutes), λ can be calculated.

FTN02 manual v1717 7/49

Figure 0.3 FTN02 in operation. The Non-Steady-State Probe TP09 (1), mounted at the
tip of the Lance, LN02 (2), is inserted into the soil. The user performs control and
readout of the experiment from the CRU02 (3), using its keyboard and LCD. The CRU02
also contains a rechargeable battery for powering the TP09. The measurement result is
immediately generated. The temperature sensor is located in the middle of the TP09
needle, 1.48 m from the top of lance LN02.

1.5 m max.

Hukseflux

Thermal Sensors

1.48 m

1.57 m

FTN02 manual v1717 8/49

Figure 0.4 For additional quality insurance, the data of the measurements can be stored
and downloaded to the PC, and reviewed using the CRU02 software (1). The CRU02 (2)
can be connected to the PC by removing a cover (4) and connecting the USB cable on
both sides (3). Visual data review is required by ASTM.

Figure 0.5 The CRU02 (1) can be recharged: Remove the cap (2), plug in the wall
socket adapter WSA02 (3) or the car adapter CA02 (4).

Chapter 1 contains information about theory of the NSSP a nd da ta analy sis, chapter 2
summarises the design criteria and chapter 3 gives general directions for performing a
measurement. After chapter 4, the instrument specifications, the remaining chapters
contain information about testing the instrument on arrival, op eration in the field,
operation of the software, calibration and maintenance.

3

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Hukseflux

Thermal Sensors

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FTN02 manual v1717 9/49

Ordering and checking at delivery

Included items

FTN02 delivery includes the following items:

• Manual FTN02

• CRU02 Control and Readout Unit

• LN02 Lance

• TP09 Thermal Properties Sensor

• PT01 Protection tube

• TC01 Transport Casing

• JR01 Jar for glycerol, with polyester fibers

• Calibration certificate for TP09

• Factory Test Certificate for CRU02

• CRU02 Manager software on Hukseflux USB flash drive

• TP09 Thermal Properties Sensor (1 piece as spare)

• CA02 Car Adapter for 12 to 24 VDC

• WSA02 Wall Socket Adapter for 220 or 110 VAC

• USB Cable for CRU02 to PC connection

Figure 0.6 FTN02 system unpacked from its TC01 transport casing

Delive ry does NOT include glycerol fluid. This has to be locally obtained by the customer.

FTN02 software can be updated by the customer. New software versions are available on
a regular basis. For available software / firmware updates, please check:

http://www.hukseflux.com/page/downloads

FTN02 manual v1717 10/49

1 Theory

1.1 General Non-Steady-State Probe Theory

For determining the thermal conductivity of materials various types of measurement
equipment can be used. In general one can make a distinction between steady-state
techniques in which the investigated sample is supposed to reach a perfect thermal
equilibrium, and non-steady-state techniques. In non-steady-state techniques the
material properties are determined while the sample temperature still changes.

The main advantage of steady-state techniques is the simplicity of the analysis of
stabilised constant sensor signals. The main adva nta ges of non-steady-state techniques
are the short measurement time and the fact that the sample dimens ions do not
necessarily enter the equation.

The only Non-Steady-State technique that has been standardised is the one using a
single needle probe (Non-Steady-State Probe or NSSP) like TP09.

ASTM D5334-14 and IEEE Std 442-1981(03) “Standard Test Methods" specify the use of
the NSSP in soil and soft rock. More information about these standards can be found in
the appendices.

In general a NSSP consist s of a heating wire, representing a perfect line source and a
temperature sensor capable of measuring the temperature at this source. The probe is
inserted into the soil that is investigated. The NSSP principle relies on a unique property
of a line source: after a short transient period the temperature rise, ∆T, only depends on
heater power, Q, and medium thermal conductivity, λ:

∆T = (Q / 4 π λ) (ln t + B) Formula 1.1.1

With ∆T in K, Q in W/m, λ in W/(m·K), t the time in s and B a constant.

The thermal conductivity can be calculated from two measurements at t

1

and t2. For TP09

(6.35 mm diameter) both t

1

and t2 are higher than 100 s, and typically 150 s apart. ∆T is

the temperature difference between the measurements at time t

1

and t2, taking t = 0 at

the moment that the heating starts.

λ = (Q / 4 π ∆T) ln(t

2

/ t1) Formula 1.1.2

The sample size is n ot critical, as long as a radius around needle is covered that is
roughly 50 times the needle radius, in case of TP09 (the needle of FTN02), which has a

3.175 mm radius: 160 mm. (please note that with low conductivity media like dry sand,
glycerol and Perspex, the sample diameter can be reduced to 100 mm)

FTN02 manual v1717 11/49

Figure 1.1.1 The signal of FTN02 as a function of the natural logarithm of time. After a
transient period the graphs show linear behaviour. In this phase the slope of the graph is
inversely proportional to the thermal conductivity

λ

.

The formula 1.1.2 is a first order approximation that is only valid under certain
conditions.
The most important conditions are that the medium has reasonable thermal contact with
the probe, that the probe is not moving and that the soil is thermally sta b le. More details
can be found in the specifications and the directions for performing a measurement. More
details on the mathematics and literature references can be found in the appendix.
Whether TP09 has passed the transient period is usually apparent from the standard
deviation of the measurement result on the CRU02 screen. Alternatively it can later be
checked by review of the data that are extracted from the CRU02.

The measurements of Q, t and ∆T are all direct measurements of power, time, and
temperature and are done without need of reference materials. The measurement with
FTN02 is absolute.

Apart from the term “thermal conductivity”, also the term "thermal resistivity" R

th

is

often used.

R

th

= 1/ λ Formula 1.1.3

In this manual only the term thermal conductivity is used.

1.2 Data analysis in the CRU02

Because of the variable conditions in fie ld measurements, data analysis of the
measurement results is hard to automate. In the CRU0 2 a firs t result is calculated by
analysis of the last half of the measurement cycle. Taking a heating time of H seconds
(typically 300 seconds), the last half is typically 150 seconds. Of this last half, the slope
is calculated over several intervals; 0.5H, 0.4H, 0.3H and 0.2H. Both the average and the
standard deviation, expressed as a percentage of the average, are calculated.

∆T

low λ

high λ

FTN02 manual v1717 12/49

1.3 Data review on PC

The data review on PC can serve to increase the reliability of the measurement. The
general idea is that with automatic analysis, there still is the risk of wrong data being
accepted.
The figures below give an example of data analysis within Excel, using the measured
date that are downloaded from the CRU02 to the PC.

Figure 1.3.1 Typical measurement results in agar gel and dry sand. The thermal
conductivity's are 0.6 and 0.3 respectively. The linear portions of the graph have to be
selected by the user. The graph illustrates that the portion that is suitable for analysis
changes from one medium to the other.

Figure 1.3.2 Example of data analysis in Excel. See also formula 1.1.1. A linear portion
of the graph of the figure 1.3.1 has been selected. The temperature T has been
multiplied by 4

π

and divided by the heating power per meter. The Excel program can
automatically calculate the best linear fit. The end result for the thermal conductivity's is
1/3.608 and 1/1.559, which is 0.27 and 0.64 W/(m·K) respectively.

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8

ln (t i me) s

Sensor Output mV m / W

agar
sand

y = 3.6082x + 9.3593

y = 1.5594x + 6.8217

0

5

10

15

20

25

30

35

40

0 2 4 6 8

ln (t i me) s

Sensor Output 4 pi T m / W

agar
sand
Lineair (s and)
Lineair (agar)

FTN02 manual v1717 13/49

2 FTN02 design considerations

FTN02 has been designed:

1. To be suitable for field surveys for electric cable trajectories and trajectories of

heated oil pipelines.

FTN02's primary focus has been on the capability to perform field measurements.
This implies that it is able to perform measurements without external power
source and that the system is sufficiently robust to survive m anual insertion into
most common soils. The system runs as a stand-alone unit, powered by the
batteries in the CRU02. Recharging can be done by a 12V DC source or a car
battery using the CA02, or on 220/110 VAC using the WSA02 adapter.

2. To save costs and time.

Many cables and pipelines are buried at a depth of around 1.5 m. The long lance,
LN02, 1.5 m, serves to avoid the necessity to dig a large access hole. In general a
small-diameter hole (typically 30 mm in diameter) is drilled to a depth just above
the required depth of measurement (generally using a ground drill). After this the
lance LN02 is inserted. The probe TP09 itself (the 17 cm tip of LN02) is then
brought down (hammered or by manual force) into the undisturbed soil.

3. To be compliant with existing standards.

For institutes that prefer to work according to standardised procedures: The
measurement with FTN02 is compliant with the ASTM standards D5334-14 and
IEEE Std 442-1981(03).

4. To produce relatively simple measurement results, allowing on site automatic

measurement as well as subsequent review on PC using stored data.

Automatic processing and visual review: CRU02 automatically processes the
measurement data, and gives both an end-result and a q uality indication of the
measurement. The FTN02 has a fairly simple signal analysis, only involving the
conversion of the signal to a logarithmic scale, and establishing the slope of the
curve. CRU02 can archive 50 measurements. In case of review, the end result is
preferably checked and recalculated by analysis of the measured data in a
spreadsheet (like Excel) or a mathematical program. Note: Hukseflux as well as
ASTM recommend performing a visual data review, using the stored data.

5. To have a traceable calibration that can be repeated on site.

Local Calibration: the FTN02 measurement is absolute and traceable to the
measurement of the heater resistance and the Pt1000 properties. For all practical
calibration purposes however, it is recommended to use glycerol at 20

o

C which is
easily obtainable and has a well establis hed thermal conductivity. Verification of
the stability of the total system can be done by repeate d (half-yearly) testing in
glycerol. This test can also be performed in the field.

6. To be locally serviceable.
The FTN02 measurement is absolute and traceable to the measurement of the
heater resistance and the Pt1000 properties. For all practical calibration purposes
however, it is recommended to use glycerol at 20

o

C which is easily obtainable
and has a well established thermal conductivity. Verification of the stability of the
total system can be done by repeated (half-yearly) testing in glycerol. This test
can also be performed in the field.

7. To allow entering software updates by the user.
New software versions can be sent over internet and loaded into the CRU02 by
the user.

FTN02 manual v1717 14/49

3 General Directions for Performing a

Measurement

The measurement must be performed conforming to the following procedures:

1. Make sure that the probe has good thermal contact to the soil.

In case of large air gaps between probe and soil, the soil should be compressed
again by hand to the original density. In case this is not possible filling material
(loose sand, silicone based thermal paste, toothpaste) can be used.

2. Verify that the probe is not moving before and during the measurement.

The measurement technique introduces a heat flow into the material. It is assumed
that this heat is transported by conduction and that ther e are no temperature
changes caused by other sources. The probe is supposed to be static before and
during the actual experiment.

3. Set up the correct power level.

The heating voltage of FTN02 can be adapted. In badly conducting soils, like dry
soil, there is less need for heating than in well conducting soils. If possible, do not
heat more than necessary.

4. Wait for thermal equilibrium.

After inserting the probe into the soil, wait for at least 5 m inutes before starting a
measurement. For example: when bringing a probe from a hot environment into a
relatively cold soil, the probe will need some time to adapt. The CRU02
automatically waits for sufficient equilibrium. This can be overruled, but it is
recommended not to do this.

5. Work at the highest possible level of reliability.

Replace bent probes as soon as practically possible.

6. Work at the highest level of quality assurance.

Whenever possible perform calibrations in glycerol as a check of good instrument
performance. This measurement can also be performed in the field.

7. Work at the highest level of quality assurance.

Optimal results are obtained when measurement results are critically reviewed
before final acceptance. First of all this should be done against common
experience. (see appendix about expected values). Also visual data review is
recommended if possible.

8. The procedures as recommended in the ASTM and IEEE standards offer a good

guideline, but do not need be followed under all conditions.

FTN02 manual v1717 15/49

4 FTN02 Specifications

4.1 Specifications of FTN02

FTN02 Field Thermal Needle System for Thermal Conductivity / Resistivity Measurements
is used for determining the thermal conductivity or resistivity of the soil in which it is
inserted. It consists of a LN02 (Lance), which serves to support the TP09 (Non-Steady­State Probe), CRU02 (Control and Readout Unit), WSA02 and CA02 adapter s. FTN02 is
supplied with CRU02 Manager Software for the collection, archiving and review of data.

Table 4.1.1 Specifications of FTN02 (continued on next pages)

GENERAL SPECIFICATIONS

Measurement
method

Absolute measurement, according to the standards
ASTM D5334-14 and IEEE Std 442-1981(03).

Specified
measurements

Thermal conductivity of soils as specif ied under suitable soils.
Directions from the manual should be followed.

Suitable soils

Granular soils (grain size smaller than 3 mm), soils, slurries, mud

and soft rock in the thermal conductivity (λ) range of 0.1 to 6

W/(m·K). Essentially this includes all known soil types.

Soil requirements

Preferably the soil is in good conta ct with the TP09 needle. Hard

soil or soft rock may be pre-drilled. Filling material may be used
to promote contact. The soil must be thermally stable (dT/dt < 1
% of the heater induced change typically, 5 % max) and
reasonably homogeneous.
In case of soil samples: please consult Hukseflux about

alternative needles.

Duration of the
heating cycle H

H must be as short as medium and readout allow. 300 seconds
(typical). Empirically verified for each soil type.

Heating Power /

meter Q

Q must be as low as the medium and readout allow. Typically Q

is adjustable so that the temperature rise is no more tha n 3 °C.

Typically lower than 5 W/m.

Temperature ra n g e

-30 to +80 °C (TP09)
0 to +80 °C (CRU02 and Cable)

Protection class

IP68 (TP09 and LN02) IP64 (CRU02)

ISO requirem en ts

FTN02 is suitable for use by ISO certified laboratories

Shipment

Total we ig h t including all access ories & packing: 15 kg (net 12.2

kg)
Dimensions: incl. packaging 1800x500x200 mm (transport case

TC01 is 1750x400x125)

CE requirements

FTN02 complies with CE directives

MEASUREMENT SPECIFICATIONS

Data analysis

First automatic analysis: by CRU02

Second review: Using CRU02 software on the PC the stored data
can be transmitted from the CRU02 to the PC and be exported to

a spreadsheet (Excel) or a dedicated mathematical program.

Expected accuracy

Thermal conductivity: ± (6 % +0.04 W/(m·K) for homogeneous

soils with good contact to the probe.

Temperature reading: +/- 4 oC

Repeatability

Thermal Conductivity: ± 2 %

Temp. dependence

< ± 0.04 %/°C after correction of Pt1000 temperature
dependence