Metrological Assessment of Distributed Temperature Sensing Techniques · · 2016-10-24Sensing Techniques. Introduction G. Failleau, ... Signal processing Display / Data file Interrogator

Laboratoire commun de métrologie LNE-Cnam

G. Failleau , O. Beaumont, R. Razouk, F. Martinot, B. Courthial,J. Bertrand, S. Delepine-Lesoille, S. Plumeri, B. Hay

Metrological Assessment of

Distributed Temperature

Sensing Techniques

Introduction

2G. Failleau, 12th of October 2016

Management of the nuclear wastes repository sites

Management of the nuclear power plants, and hydrolics dams and dikes

Thermal instrumentation and metrology, development of new calibration capabilities

Distributed Temperature Sensing

Partnership LNE – EDF - Andra

http://www.decommissioning-emrp.eu /

Outlines


I. Fundamentals on Distributed Temperature Sensing by Raman Scattering

II. Development of testing facilities suitable to DTS devices

III. Assessment of a few metrological performances

IV. Conclusions and outcomes



Raman ScatteringV

irtua

l en

erg

y le

ve

ls

En

erg

y leve

l

Vib

ratio

nn

al s

tate

sIn

tensity

� Inelastic collision (Excitating photon Vs. Crystal lattice)

� Energetic transition between two vibrationnal state s of the lattice

� Emission of a Stokes radiation : most probable case (i.e Bose-Einstein distribution)

� Emission of an Anti-Stokes radiation : less probable, depending of the temperature

The ratio of Stokes & Anti-Stokes intensities is dependant with the temperature

2


Distributed Temperature SensingApplication to the optical fibres

Acrylate coating (dia. 250 µm)

Core (dia. 50 µm)

Cladding (dia. 125 µm)

� Technologies based on the Optical Time Domain Reflectometry (OTDR)

� The optical fibre is the sensitive element

� Multimode optical fibres used as sensors (Telecom. standard)

� Fibres interrogated by nano-second pulsed laser (typically 1064 nm)

� Continuous measurement along the whole length of the optical fibre

� Absolute spatial resolution (sampling resolution) of 1 m

� Measurement range : 0 – 30 km

� Typical operating range : -5 – 90 °C (depending of the optical fibre intrinsic properties)

Tem

pera

ture

Distance

Measured temperature profile

Pulsed laser source

Detection

Laser pulse (pump)

Backscattered light

Sampling resolution

Signal processingDisplay / Data file

InterrogatorSensing optical fibre



Temperature monitoring by conventionnal thermometer s

� A few hundreds/thousands sensors by structure� ~100 € - 200 € per sensor

Underground nuclear waste repository sites

Dikes

Dams

But also… Tunnels, gas & oil pipelines, etc…



Temperature monitoring by optical fibres

� A few hundreds/thousands measurements over the fibre length� ~0,20 € / m

Underground nuclear waste repository sites

Dikes

Dams

But also… Tunnels, gas & oil pipelines, etc…

Expected sources of error


Interrogator

Temperature Mechanical constraints

Ionizing radiations

Source

Detection

Temperature

Humidity and chemical pollutions

The interrogator and the optical fibre are influenced by the environmental conditions :

� Changes of the optical fibre properties (attenuation factor, refractive index variations ,…)

� Influence of the temperature on the interrogator optics and internal reference

� Mechanical constraints on the fibre (curvature radius…)

Achievements

DTS devices commercially available but lack of stan dardization


� To identify relevant metrological characteristics to be evaluated

� To develop experimental facilities suitable to DTS devices

� To define experimental methods and protocol for testing the DTS devices

� To provide a benchmark on DTS devices for the users

Finaly, to propose new standards devoted to the DTS methods

Outlines




III. Assessment of a few metrological performances


Calibration facilities


� Implementation of a reference optical fibre (length of 5, 10, 15, or 20 km)

� Interrogator and optical fibre thermally decoupled (thermal enclosures)

� Thermal conditions rigorously controlled (trueness, stability, temperature homogeneity)

� Mechanical constraints controlled ( « constraint free » optical fibre wound )

� Temperature stability within 0,02 °C

� Temperature homogeneity within 0,1 °C

23.09

23.10

23.11

23.12

23.13

23.14

23.15

23.16

23.17

23.18

23.19

0 1 2

Tem

pé

ratu

e,

°C

Temps, hTime, h


Calibration facilities

� Implementation of a reference optical fibre free from any mechanical constraint

� Operating range : ~ 0°C up to 90 °C

� Temperature stability within 0.05 °C over 5 hours, thermal homogeneity within 0.2 °C over 23 m

Horizontal furnace with 25 m of length

30.005

30.010

30.015

30.020

30.025

30.030

30.035

30.040

30.045

30.050

30.055

5 15 25 35 45 55

Tem

pera

ture

, °C

Time, h

static PRT

mobile PRT

0.01 C

Thermal stability at 23 °C

Outlines




III. Assessment of metrological performances



Metrological characteristics

� Spatial resolutionThe shortest length of optical fibre which has to be immersed into a thermally homogenousenvironment for measuring the true temperature value.Depending of the sampling interval, optical pulse width .

� Spatial dispersionThe lowest temperature gradient which can be measured over a length of optical fibre corresponding to 10 times the spatial resolution.Depending of the optical pulse broadening (chromatic & intermodal dispersions), signal-to-noise ratio, spatial resolution, integration time.

� Temporal dispersionRepeatability of the temperature measurement one one given point of the optical fibre over 10 successive measuring cycles over time.Depending of the optical pulse broadening, signal-to-noise ratio , spatial resolution.

� Trueness errorComparison of the temperature measured by the DTS-Raman to the temperature measured by a Standard Platinum Resistance thermometer (SPRT)Depending of the interrogator temperature, optical fibre temperature.


Benchmark on Raman-DTS devices

Device A Device B

� Quantifying the metrological characteristics of DTS -Raman devices

� Proposing a relevant comparison to the end-users

15

17

19

21

23

25

27

29

0 5000 10000 15000 20000

Tem

pe

ratu

re (

°C)

Position (m)

15

17

19

21

23

25

27

29

0 5000 10000 15000 20000

Tem

pe

ratu

re (

°C)

Position (m)

Similar temperature traces obtained at 23 °C, but…



-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

0 5000 10000 15000 20000

Tru

en

ess

err

or

(°C

)

Position (m)

23 °C (initial) 3°C

23 °C 40 °C

60 °C

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0 5000 10000 15000 20000

Tru

en

ess

err

or

(°C

)

Position (m)

23 °C (initial) 3 °C

40 °C 60 °C

23 °C

Device A Device B

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5000 10000 15000 20000

Sp

ati

al

dis

pe

rsio

n (

°C)

Position (m)


40 °C 60 °C

23 °C

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

0 5 000 10 000 15 000 20 000

Sp

ati

al

dis

pe

rsio

n (

°C)

Position (m)


23 °C 40 °C

60 °C


Device A Device B


0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0 5000 10000 15000 20000

Tem

po

ral

dis

pe

rsio

n (

°C)

Position (m)


23 °C 40 °C

60 °C

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 5000 10000 15000 20000

Tem

po

ral

dis

pe

rsio

n (

°C)

Position (m)


40 °C 60 °C

23 °C

0.0

20.0

40.0

60.0

80.0

100.0

0 1 2 3 4 5 6 7 8

Re

spo

nse

to

a t

em

pe

ratu

re s

tep

(%

)

Optical fibre length immersed at 0 °C (m)

Sampling 1 m - Resolution 1 m

Sampling 0.5m - Resolution 1 m

Sampling 0.5 m - Resolution 2 m

Re

solv

ed

me

asu

rem

en

t

Re

solv

ed

me

asu

rem

en

t

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8

Re

spo

nse

to

a t

em

pe

ratu

re s

tep

(%

)

Optical fibre length immersed at 0 °C (m)

Sampling 1 m

Sampling 0,1 m

reso

lve

d m

ea

sure

me

nt

Re

solv

ed

me

asu

rem

en

t

Outlines




III. Assessment of metrological performances


Conclusions & outcomes


� Development of calibration facilities suitable with DTS

� Metrological characteristics identified

� Influence factors identified

� Development of a characterization protocol suitable to DTS

� Benchmark on DTS devices to be performed

� Toward a normalized frame (procedures to be proposed to IEC)

Our goal is to ensure the metrological traceability to the measurements performed by DTS


Thank you for your attention

… Any question(s) ?

Documents

Metrological Assessment of Distributed Temperature Sensing Techniques · · 2016-10-24Sensing Techniques. Introduction G. Failleau, ... Signal processing Display / Data file Interrogator