Un sensore a fibra ottica per misure di temperatura in situ in prove tribologiche

A&T International exhibition - APRIL 20th-21st 2016 1

Un sensore a fibra ottica per misure di

temperatura in situ in prove tribologiche

Lucia Rosso1, Vito Fernicola1, Shahin Tabandeh1

1 INRIM- ISTITUTO NAZIONALE DI RICERCA METROLOGICA


Scope of the project

An EMRP joint research project “Metrology to assess the durability and function of engineered

surfaces” (JRP IND 11 MADES) was trying to address fundamental aspects of metrology for tribology

in order to improve the long-term performance of tribological surfaces in industrial applications.

Durability and performance of many products and engineering devices depend critically on

tribological properties of the surfaces, such as wear and friction.

The temperature at wear interface - contact point between the surfaces - has a major influence on

the tribological performance of the materials.


Pin-on-Disk wear testing(ASTM G99-04)

• Pin-on-Disk testing consists of a flat rotating disk in contact with a fixed perpendicular pin

with a radius tip. The pin is pressed against the disk at a defined load.

• Both the normal and friction forces are measured by transducers. Performance is generally

characterized by friction coefficient and wear rates determined by mass or volume loss.

Load

PinWear track

Disk


Optical fibre

Blind hole

Ruby hemisphere

Modified Pin-on-Disk probe

• The original sapphire pin tip is replaced by a

machined ruby half-sphere.

• Ruby (Cr-doped sapphire) is a well-known

temperature sensitive material.

• The pin becomes, at the same time, the

wear test probe and the temperature sensor

at the contact point!


Ruby-based fibre optic probe for in situ temperature measurements

ST-connectorRuby pin

Optical fibre

& silica tubing Cap

blind hole

O.D.= 20 mm


Temperature response curve of the sensor probe calibrated by immersion

Caveat: sensor calibration was carried out in a thermostatic medium, but sensor operation is far

from thermal equilibrium!

Ave. temperature

sensitivity is 10 µs/°C

� � ��

1 � 3��

��

1 � ��

��

� � ��

1 � 3��

��

1 � ��

��

Std. dev. = 0.1 °CTemperature

[°C]

Life time

[ms]

Std.dev.

[µs]

25.92 3.1065 1

49.99 2.8693 0.9

100.70 2.2813 1.2

149.69 1.6213 0.5

200.33 1.0364 0.3

T/ K

τ/

ms

τ/

ms


Sensor response to 200°C step input

TS

Tpin

TS

heat flux

Time/ S

Temperature/ °C


Finite element modeling

TS

convection

insolationinsolation

T=TsThermal contact resistance is unknown


Surface temperature calibration: experimental results & model validation

Reference

PRTs

Pin-on-disk

temperature

probe

0

5

10

15

20

25

0 25 50 75 100 125 150 175 200Tem

pe

ratu

re

err

or

/ °C

Surface temperature / °C

model

Experiment


CFD modelling of the probe-surface contact

Glass-

ceramic

Low TC

polyamide

Ruby

hemisphere


0

50

100

150

200

250

Third partial error 3b

Third partial error 3a

Second partial error

Tpin

Partial temperature errors(Ts=200°C)

20.54 °c14.34 °C

2.84 °c


Model-based compensation Idea

T��

TRuby

Ttip ?T��

TRubyTtip

ModelT��

TRubyTtip

model


Tpin - Tthermistor / °C

NTC

Tem

pe

ratu

re e

rro

r /

°C

0 20 2515105

20

0

40

60

120

80

100

140

160

180

30

Temperature error at the probe-surface contact: heat flux and transient studies


Temperature error at the probe-surface contact:modelling the transient

Tth

erm

isto

r /

°C

Tpin / °C

Blue lines are

transient measured

temperature and red

line is the model

steady state output

The red line turns to be unique for

different possible experimental layouts

and thus used for A.N.N. training

Tsurface

= 200 °C

Set of arbitrary values

?


Tthermistor

Tpin

Inputlayer

Hiddenlayer

Hiddenlayer

outputlayer

Artificial neural network training

Surface temperature / °C

Tem

pe

ratu

re

err

or

/ °C

Ttip


“ANN” vs “surface calibrator”

temperature error compensation

The temperature estimation at 98 % of

the final value is >3 times faster

Time / s

Advantages of ANN compensation:

o More than 3 times faster

o Applicable for live error compensation in tribometers


Operation of the probe in tribometers

P=20N

TRuby Tthermistor Tcompensated

Tmin [°C] 22.01 22.63 21.69

Tmax[°C] 29.76 25.78 31.83

∆T[°C] 7.75 3.15 10.14

Truby Tthermistor Tcompensated

Tmin [°C] 22.41 23.28 21.98

Tmax[°C] 29.90 26.24 31.81

∆T[°C] 7.48 2.96 9.83

Time/ S Time/ S

Temperature/ °C

Temperature/ °C



Temperature/ °C

P=40N P=60N P=80N

∆T=19.74°C∆T=30.78°C ∆T=40.11°C

Time/ S



Normal load/ N

∆T

/ °C

∆T=0.5051*P+0.318


Conclusions

A fibre-optic point sensor for in situ temperature measurements was developed.

The sensor - based on the fluorescence thermometry method - was integrated

into a modified pin-on-disk wear test facility, together with a portable

fluorescence excitation/detection module.

The temperature probe was studied over the range 20 °C to 200 °C.

Finite element modelling identified the main limitations of the method and

helped to compensate for large intrinsic temperature errors.

An ANN model was developed for live passive compensation of the temperature

error and yeilded to a faster time responce.

Operation of the probe was succesfully chechecked in a tribometer.

An expectated linear trend was evident in the ΔT vs P diagram.


Thank you!

[email protected]

Date post:	26-Jan-2017
Category:	Technology
Upload:	togethertosolve
View:	30 times
Download:	0 times

Un sensore a fibra ottica per misure di temperatura in situ in prove tribologiche

Technology