RESPONSE TIME OF HYDROGEN SENSORS

Thomas Hübert and Ulrich Banach

BAM Bundesanstalt für Materialforschung und -prüfung, Berlin, Germany,

thomas.huebert@bam.de

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Id 124

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IntroductionExperimental Sensors

Sensor Testing Facility

ResultsComparison with results from literature

Influence of hydrogen concentration on step respons e

DiscussionContributions to delay time of sensors

Modeling of response and recovery time

Characteristic parameters

Summary

Outline

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Introduction

…. seconds are vital !

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Introduction

…. seconds are vital !

Conversely the recovery time (t10) is taken for a sensor to reach

10 % of the preceding response following exposure to air.

to define the speed of response of gas sensors

usual parameters for sensor characterization:

interval, between

the time when an instantaneous variation between clean air

and the (hydrogen containing) test gas,

or vice versa, with the sensor in a warmed-up condition,

is produced at the sensor inlet, and

the time when the response reaches a stated percentage of the stabilised signal

on the standard test gas (ISO 26142).

Response time (t90):

The time taken for a sensor to reach 90 % of the final indication.

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Requirements on hydrogen sensors

indication range 0.01 - 10 % hydrogen (safety) or 1 - 100 % (fuel cells)

safe performance, i.e. explosion proof sensor design and protective housing

reliable response, sufficient accuracy, sensitivity (uncertainty 5 - 10 % of signal)

stable signal with low noise

robustness including low sensitivity to environmental parameters such as:

temperature (-30 to 80 °C (safety), -70 to 150 °C (fuel cells),

pressure (80 to 110 kPa)

relative humidity (10 to 98 %),

gas flow rate independence,

mechanical robustness

fast response and recovery time (5 years)

low power consumption (

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Requirements on hydrogen sensors

fast response and recovery time

different requirements:

ISO 26142 (hydrogen fuel station)

t90 < 30 s

t10 < 60 s

Stationary Power Systems

t90 < 30 s

t10 < 30 s

Car Manufacturer

t90 < 1 s

t10 < 1 s

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Experimental Sensors

Two semiconductor MOS-type sensors (MOS I), (MOS II).

Metal-insulator-semiconductor field effect transistor (MIS-FET)

Schottky diode (RT-Diode)

Field effect based sensor (RT-FES).

Schottky Diode

metal

interfacial layer

semiconductor

MOS Field-Effect Transistor

metalinsulator

semiconductor

S D

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Experimental Sensor Testing Facility

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Experimental Sensor Testing Facility

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Results

0 5 10 15 20

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

hyd

roge

n am

ount

in te

st g

as in

% H

2

sens

or in

dica

tion

in %

H2

time in s

ts

0 5 10 15 20

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

hyd

roge

n am

ount

in te

st g

as in

% H

2

sens

or in

dica

tion

in %

H2

time in s

ts

hydrogen on hydrogen off, purging with air

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Results

Sensor Response times t90 (s) Recovery timet10 (s)MOS I 2 - 6 10 - 12 MOS II 5 - 16 13 - 50

MIS-FET 3.3 - 3.5

2.1 - 2.3

10.2 - 10.3

6.8 - 6.9RT Diode 150 - 200 100 - 300RT FES 10 - 15 50 - 70

Sensor type

Response This work (s) Results from literature (s)

Source

MOSt90 2 - 6

16≤ 15

[8][9]

t10 10 - 1212

< 30 [8][9]

MIS-FETt90 2.1 - 2.3

< 22 - 4

[10][2]

t10 6.8 to 6.9< 109.2

[10][2]

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Results Influence of hydrogen concentration on step respons e

0 200 400 600 800 1000

0

1

2

3

4

5

6

20

30

40

MOS (TGS) Mishra

resp

onse

tim

e in

s

hydrogen concentration cH2

(µL/L)

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Discussion Contributions to delay time of sensors

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Discussion Modeling of response and recovery time

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Discussion Modeling of response and recovery time

0 10 20 30 40 50

0,0

0,5

1,0

MOS I MOS II FIS-FET RT-Diode RT-FE

S(t)rel

time in s0 10 20 30 40 50 60 70 80 90 100

0,0

0,5

1,0

MOS I RT-Diode MIS-FET RT-FET MOS II

time in s

S(t)rel

Signal increase Signal decrease

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Discussion Modeling of response and recovery time

SensorResponse time

1-exp(-t/τ)Recovery time

exp(-t/τ´)

τ r τ‘ rMOS I 2.1±0.1 0.90 4.1±0.2 0.94MOS II 14.7±0.1 0.99 75±4 0.96

MIS-FET 1.5±0.1 0.98 6.3±0.6 0.91RT Diode 81±3 0.99 45±4 0.92RT-FES 2.9±0.2 0.96 22.3±1.4 0.94

Sensor Response times t90 (s) Recovery timet10 (s)MOS I 2 - 6 10 - 12 MOS II 5 - 16 13 - 50

MIS-FET 3.3 - 3.5

2.1 - 2.3

10.2 - 10.3

6.8 - 6.9RT Diode 150 - 200 100 - 300RT FES 10 - 15 50 - 70

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Discussion Further characteristic parameters

first response:

t20

t50

alarm:

20 % UEG (0.8 % H2)

40 % UEG (1.6 % H2)

shorter time of responses (< 1 s) are achievable.

Sensor indication of:

alarm:

use of fitted response curves

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Summary

IntroductionExperimental Sensors : MOS, MIS-FET, RT-Diode, RT-FES

Sensor Testing Facility : “delay time” 4 s and 1 0 ms

Resultst90 < 10 s and t 10 < 20 s

H2 concentration on step response

DiscussionContributions to delay time of sensors

Modeling of response and recovery time

Characteristic parameters: first response ( t10) , alarm time (20 % UEG)

PD Dr. W. Moritz and colleagues

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Acknowledgements

FCH JU financial support Contract No. 325326

Humboldt University of Berlin

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Thank you for your attention !

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