MicroChemical Systems
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MiCS – 5131
Ethanol Gas Sensor
This datasheet describes the use of the MiCS-5131 in breathalyzer applications. The package and the
mode of operation illustrated in this document target the detection of ethanol in the human breath.
Features:
•
•
•
•
•
•
•
Low heater current
Wide detection range
High sensitivity
Fast thermal response
Electro-Static Discharge protected
Miniature dimensions
High resistance to shocks and vibrations
This Product Data Sheet accompanies MicroChemical Systems MiCS-5131 sensors for ethanol. Reproduction and distribution of this document is
restricted by MicroChemical Systems. The following specifications are subject to change to accommodate continuous improvement.
For this and other quality MiCS products, send an e-mail to
info@microchemical.com
or contact MicroChemical Systems at:
Rue de Porcena 15
•
CH-2035 Corcelles, Switzerland
•
Tel: 41 (0) 32 731 0120
•
Fax: 41 (0) 32 731 0124
MiCS-5131 Product Data Sheet
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Sensor Characteristics
Important Precautions:
Please read the following instructions carefully before using the MiCS-5131 sensor described in this
document to avoid erroneous readings and to prevent the device from permanent damage.
•
The sensor must not be wave soldered without protection or exposed to high concentrations of organic solvents,
ammonia, or silicone vapors in order to avoid poisoning the sensitive layer.
•
Heating powers above the specified maximum rating of 120mW can destroy the sensor due to overheating.
•
This sensor is to be placed in a filtered package that protects it against any water or dust projection.
•
For any additional questions, please contact us at:
apps@microchemical.com
Operating Mode:
The recommended mode of operation is a constant power
mode. A heater power of P
H
= 102 mW is applied. This
causes the temperature of the sensing resistor (R
S
) to
reach about 450°
C.
Detection of ethanol is achieved by measuring the sensing
resistor R
S
during operation.
Measurement Circuit:
Figure 2 shows the pin connections of the MiCS-5131 gas
sensor. A simple circuit to measure the ethanol level is
proposed in Figure 3. The heating voltage V
H
is applied to
pins 3 and 1. A load resistor R
L
is connected in series with
R
S
to convert the resistance R
S
to a voltage V
S
between
pins 2 and 4. R
S
can then be calculated by the following
expression:
R
S
= R
L
/(V
CC
- V
S
)
⋅
V
S
Sensor Response:
The sensor response to ethanol in air is represented in
Figure 1. The sensor resistance R
S
is normalized to the
resistance under air (R
0
).
1
3
R
H
4
2
R
S
1
Pin Number
1
2
3
4
Heater Ground
Sensor Pin
Heater Power
Sensor Pin
R
S
/R
0
Figure 2: Equivalent circuit (top view) of MiCS 5131.
V
CC
Gas
Sensor
3 2
0.1
10
100
1000
V
H
Ethanol [ppm]
4 1
V
S
R
L
GND
Figure 3: Measurement circuit for ethanol detection.
Figure 1: R
S
/ R
0
as a function of gas concentration
at 50% RH and 25°C.
MiCS-5131 Product Data Sheet
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Cross Sensitivity:
The following figure illustrates the MiCS-5131 cross
sensitivity to CH
4
, CO, C
2
H
5
OH and H
2
.
1
Temperature and Humidity
dependence:
Temperature and humidity also affect the resistance value
of the sensor. Humidity is water (H2O) in gas phase, which
reacts with the sensing layer like a reducing gas.
Increasing humidity causes a decrease of the sensing
resistance. As for the temperature, the effect is the same
as for the humidity, i.e. decreasing resistance with
increasing temperature. This negative temperature
coefficient is due to the semiconductor properties of the
sensing layer material.
Rs / Rair [-]
10
CH4
CO
Rair / Rair,25°
C-50% RH [-]
Rs/Ro 20%
Rs/Ro 50%
Rs/Ro 70%
Rs/Ro 90%
0.1
10
C2H5OH
H2
100
concentration [ppm]
1000
1
Fig. 4: Sensitivity to CO, H2, CH4, and C2H5OH at
25°C and 50% RH.
Response time:
A typical response curve under laboratory conditions is
shown in figure 5. The test gas is 60ppm of C2H5OH and
the sensing resistance reaches 90% of its final change in
about one second.
0.1
0
20
40
Temperature [°
C]
60
80
Fig. 6: Temperature dependence of baseline
resistance Rair for 20%, 50%, 70% and 90% RH.
1.2
1
0.8
Rs / R0 [-]
0.6
0.4
0.2
0
-10
-5
0
time [second]
5
10
Fig. 5: Response time to 60ppm C2H5OH
MiCS-5131 Product Data Sheet
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Electrical Specifications
Maximum Ratings:
Rating
Maximum Sensor Supply Voltage
Maximum Heater Power Dissipation
Maximum Sensor Power Dissipation
Relative Humidity Range
Ambient Operating Temperature
Storage Temperature Range
Storage Humidity Range
Table 1
Symbol
V
CC
P
H
P
S
R
H
T
amb
T
sto
RH
sto
5
-40
-40
5
Value / Range
5
120
1
−
−
−
−
95
120
120
95
Unit
V
mW
mW
%RH
°
C
°
C
%RH
Operating Conditions:
Parameter
Heating Power,
[1]
Heating Voltage,
Heating Current,
Heating Resistance,
[2]
Table 2
[1]
Symbol
P
H
V
H
I
H
R
H
Typ
102
3.2
32
100
Min
85
-
-
90
Max
120
-
-
110
Unit
mW
V
mA
Ω
A minimum value of 85mW ensures sufficient sensitivity to ethanol. Heating powers above 120mW can cause permanent
damage to the sensor when ambient temperatures exceed 120°C.
Heating resistor values from sensors out of production range between 90 and 110 Ohm. Due to material properties of the
heating resistor its value increases during operating life. This behavior has to be taken into account in the application
design.
[2]
Sensitivity Characteristics:
Characteristic
Ethanol Detection Range
Sensing Resistance in air
Sensitivity Factor
Table 3
[3]
[4]
[4]
[3]
Symbol
FS
R
0
S
R
Typ
24
1.4
Min
10
18
1.3
Max
1000
180
1.8
Unit
ppm
k
Ω
-
Sensing Resistance in air R
0
is measured under controlled ambient conditions, i.e. synthetic air at 23±2°C and 50±5 %RH.
Sensitivity Factor S
R
is defined as R
S
at 60ppm of CO divided by R
S
at 200ppm of CO. Test conditions are 50±5 %RH and
23±2°
C.
MiCS-5131 Product Data Sheet
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Package Dimensions and Filter
J
A
B
C
H
I
K
D
E
Dimension
A
B
C
D
E
Min [mm]
9
8.15
5.75
0.6
3.5
9.0
12.5
2.41
0.55
4.83
0.7
Max [mm]
9.15
8.30
5.85
0.9
3.9
10.0
13.9
2.67
0.65
5.33
0.9
G
F
F
G
H
I
J
K
MiCS-5131 Product Data Sheet
Page 5 of 5
Doc NO: 0178 Rev. B
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