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RESPONSE TIME OF HYDROGEN SENSORS
Thomas Hübert and Ulrich Banach
BAM Bundesanstalt für Materialforschung und -prüfung, Berlin, Germany,
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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)
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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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