Features
• Sensitivity range: 5 to over
1000 ppm CO
• Low humidity dependence in
recommended operation mode
• Stable long-term operation
• Active charcoal filter for
enhanced selectivity
• Low power consumption
• Small size
• Durable nylon exterior shell with
steel mesh Sensor Pin
Application examples
• Security
• Residential CO Detectors
• Industrial Stationary and
Portable CO Detectors and Probes
• Combustion control
• Environment
• Indoor air quality
• Industrial process control
Microsens Semiconductor Gas Sensor
MSGS-3001 Carbon Monoxide Gas Sensor
General description
Operating principle
The measurement of specific oxidizing
or reducing gases is based on reversible
conductivity change of the sensing
element.
Sensor description
MSGS-3001 Integrated semi-
conductor carbon monoxide (CO) gas
sensors are manufactured using
standard microelectronic technology
and silicon micromachining techniques.
The batch fabrication process of
MSGS-3001 miniaturized gas sensors
presents the advantages of low cost,
reproducibility, small size and low
power consumption.
The MSGS-3001 structure consists
of a doped tin-oxide (SnO2) thin-film
layer over an embedded thin film heater
(figure 1). This integrated heater
resistance (RH) is used to control the
sensitive layer temperature which is
necessary for Chemisorption/Reaction
mechanisms to properly occur. These
mechanisms modifies the sensitive
layer resistance (RS) by reversible
electron charge transfer from surface
states to the conduction band.
The operating temperature is
controlled by VHapplied on the heater
resistor (RH). A polarization voltage (VS)
is applied to the sensitive layer which
resistance can be mesured using
an electric circuit shown in figure 4. The
4-pins package is indicated on figure 2.
Figure 1: Schematic drawing
Sensor Contact
SiO2
Membrane
Si
Doped-SnO2
Heater
RS+VH
1
-VH
3
- (+) VS 4
+ (-) VS 2
RH
PIN NUMBER
1 Heater Power
2 Sensor Pin
3 Heater Ground
4 Sensor Pin
Figure 2: Sensor equivalent circuit
(Top View)
Table 1: Absolute Maximum Ratings
Rating Symbol Value Unit
Maximum Heater Supply Voltage (pins 1 & 3) VH2V
Maximum Heater Supply Current (pins 1 & 3) IH32 mA
Maximum Sensor Circuit Voltage (pins 2 & 4) VS5V
Maximum Heater Power Dissipation PH65 mW
Maximum Sensor Power Dissipation PS1mW
Maximum Heating Voltage Ramp tHR0.2 V/ms
Operating Ambient Temperature Tao 0 to + 50 °C
Storage Temperature Range Tsto -40 to + 70 °C
Table 2. Recommended Electrical Operating Conditions
Characteristics Symbol Typical value Unit
Heating Voltage - Low - 10 seconds (pins 1 & 3) VH0.8 V
Heating Voltage - High - 5 seconds (pins 1 & 3) VH1.8 V
Heater current - Low - 10 seconds (pins 1 & 3) IH24 mA
Heater current - High - 5 seconds (pins 1 & 3) IH31 mA
Heater Power Dissipation - Low - 10 seconds PH20 mW
Heater Power Dissipation - High - 5 seconds PH56 mW
Average Power Consumption PH32 mW
Heater Resistance (VH= 0 volt) RH(Ta) 23 W
Heater Resistance (VH= 1.8 volt) RH(THigh) 57 W
Load Resistance RL
Variable (PS<1mW)
W
Table 3. Sensitivity Characteristics3
Characteristics Symbol Typical value Unit
Sensor Resistance (in Synthetic air) RS(air) 36 MW
Sensor Resistance (in 100 ppm CO) RS(100) 4 MW
Sensor Ratio R(air)/RS(100) S(air/100) 9 ---
Sensor Ratio R(air)/RS(60) S(air/60) 6 ---
Sensor Ratio R(air)/RS(15) S(air/15) 2 ---
Sensor Ratio R(15)/RS(100) S(15/100) 4 ---
MSGS-3001 CO Sensor specifications 1-2
Standard test conditions: RH= 50 ± 2%; Ta = 23 ± 1°C. The measurement is
performed at the end of the "Low" temperature phase.
Device specifications 1
• Chip Dimensions:
1.4mm x 1.4mm x 0.38 mm
• Sensor Dimensions mounted on a
TO-39 package with a filter:
Ø = 10.3 mm; h = 24.0 mm
• Typical thermal loss coefficient:
ß = 0.12 mW/°C
ß= ÆP/ÆT; ß = P/(T-Ta)
- P = heating power (mW)
- Ta = ambient temperature (°C)
- T = gas sensor temperature (°C)
Notes:
1. The following specifications apply to the
MSGS-3001 CO sensor are subject to change
to accommodate continuous improvement.
2. The heating conditions limits must be observed
and limited as described in Table 1. Permanent
damage may occur if the maximum power is
exceeded.
3. Based on recommended operation:
VH(High temperature) = 1.8 volt (5 sec.);
VH(Low temperature) = 0.8 volt (10 sec.)
Measurement
test circuits
Two different basic electric circuits
which can be used with the gas sensors
are presented on the figure 4. The
amplifier system (2) presents however
the advantage of maintaining a
constant voltage VCon the sensitive
layer. A constant-current test circuit can
also be used for the gas sensors,
considering the recommendation of
Table 1 (maximum power sensor
dissipation of 1 mW).
Mode of operation
Principle
An operating mode based on a
sequence of two heater temperatures is
used for the CO detection. This
operating mode increases the CO
sensitivity while the influence of
humidity is minimized. During the
"High" temperature period (5 seconds),
water and contaminants are removed
from the surface of the sensitive layer,
while the thermal energy of the
adsorbed oxygen species is increased
which causes a drastically higher
catalytic conversion from CO to CO2.
The CO measurement is carried out at
the end of the "Low" temperature phase
(10 seconds).
Humidity Influence
Figure 7 presents results obtained
in different relative humidity. These
results confirm the efficiency of the
operating mode proposed to decrease
the moisture influence.
Sensors precautions
• Avoid to overheat the sensor
(see Table 1)
• ESD protection is required when
handling these devices
RH=50%
Ta=23°C
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
0 20406080100
CO Concentration [ppm]
RS(gas)/RS(100)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0 20406080100
Relative Humidity [%]
Ratio RS(gas)/RS(100 ppm CO; 50%RH)
0 ppm CO
15 ppm CO
60 ppm CO
100 ppm CO
VH
VCRLVout VCVout
RF
VH
GAS SENSOR
(GS)
GAS SENSOR
(RS)
GS=• VoutRs = • RL
(1 )
VC
Vout
1
VC•RF
+
–
(1) (2)
V
S
V
S
V
S
V
S
V
H
V
H
(G
S
)(R
S
)
(R
L
)
(R
F
)
(R
F
)
(R
L
)
R
S
G
S
Time
With CO
Without CO
Gs
High
5 sec
Low
10 sec
Point of measurement
GS = Conductance of the Gas Sensor
Figure 5: Principle of the operating mode
Figure 4: Basic electric circuit for gas sensor
Figure 6: CO Sensitivity
Figure 7: Humidity Influence (Ta=23°C)
MSGS-3001-B
TO-39 PACKAGE
MSGS-3001-D
TO-18 PACKAGE
MSGS-3001-E
PLASTIC PACKAGE
Nylon Cap
Nylon Mesh
Filter
Metal Mesh
Sensor Die
Metal Cap
Plastic Mesh
Filter
Metal Mesh
Sensor Die
Plastic Cap
16 mm
Nylon Cap
Nylon Mesh
Filter
Metal Mesh
Sensor Die
Metal Cap
16 mm
8 mm
10.2 mm
2.4 mm 0.5 mm
5.3 mm
5 mm
5 mm
7 mm max
3 pins Ø 0.4 mm
3 pins Ø 1.5 mm
Ø 9.1 mm
Ø 9.1 mm
Ø 7.6 mm
Gold wire TO 39 Package
Four pin
Sensor Die
Die size
from 3 x 3 mm
down to 1 x 1 mm
0.8 mm
0.8 mm
45°
4.2 mm
2.54 mm
0.8 mm
0.8 mm
Ø 0.35 mm
longueur = 8.5
Ø 0.43 mm
longueur = 8 mm
1
3
2
4
1
4
3
2
1
4
3
2
Packaging characteristics
The standard packaging used a TO-39 support. A charcoal filter placed in a nylon casing reduces
the effects of interfering gases.
MICROSENS SA
Rue Jaquet-Droz 1, CH-2007 Neuchâtel/Switzerland
Tél.: ++41-32-720 51 51, Fax: ++41-32-720 57 12
e-mail: microsens@centredoc.ch
