Download SENSORS AND SYSTEMS TECHNOLOGY PRODUCTS REVIEW

PRODUCTS REVIEW
SENSORS AND SYSTEMS TECHNOLOGY
PRODUCTS REVIEW
Products range, code numbers
Introduction
The basic features and primary applications of FIS
Based on its pre-eminent expertise in developing Metal
products are described on the following pages.
Oxide Semiconductor Gas Sensors, FIS today offers a
range of products covering a wide field of applications
including:
FIS also develops and supplies various products
including micro-computers, sensor evaluation units and
others such as electrochemical or optical sensors.
• Flammable gas detection
FIS always finds the most effective approach to improve
• Toxic gas detection
gas detection technologies by studying the combination
of both sensor technologies and application software.
• Indoor air quality controls
• Combustion monitoring/controls
• Cooking controls
FIS will continue to develop new sensors to meet the
demands of the marketplace.
• Ventilation controls
The new range of semiconductor gas sensors developed
by FIS has achieved an unprecedented reduction in
heater power consumption, while preserving the typical
features of semiconductor gas sensors such as:
• High reliability
• Long life
• Ease of operation
• Low cost
Products range, code numbers
The range of FIS products and the numbering system of
the different models are illustrated here.
S
Category
S: Semiconductor
L: Lambda
(semiconductor)
E: Electrochemical
P: Optical
2
P
Type
(semiconductor)
B: Bead type
P: Plate type
P3: Plate (3 pins)
P4: Plate (4 pins)
T: Tube type
C: Bulk type
- 11 - 00 - (P1)
Detection type
Sub code
Housing
Indicated in the
Products list
This sub code shows
the variation of
specifications, heater
voltage or other
conditions
(P1):
(P2):
(MC):
(MP):
(S):
Plastic - type 1
Plastic - type 2
Mesh Ceramic
Mesh Plastic
Sintered Metal
PRODUCTS REVIEW
Products list
Series
Features
SP series
• Small heater power consumption
(120 mW)
• Small size
• High sensitivity to flammable gases
• Suitable for portable detectors/
battery operated devices
• Reduced heater power consumption
using a small gas sensing element
• Low heater current
• Variation of heater voltage
• Wide variation of sensitivity
characteristics
Model (power consumption)
Model (power consumption)
Category
No
Dual gas
90-
CO and methane
SB-95 (PH : 120 mW - max.)
Flammable gases
10-19
General purpose
SB-11A (PH : 120 mW)
SP-11 (PH : 400 mW) *
Methane
SB-12A under development
SP-12A (PH : 380 mW)
Propane/butane
SB-15 (PH : 120 mW)
SP-15A (PH : 380 mW)
Hydrogen
SB-19 (PH : 120 mW)
SP-19 (PH : 315 mW)
General purpose
SB-31 (PH : 120 mW)
SP-31 (PH : 315 mW)
Alcohol
SB-30 (PH : 120 mW)
SP-32 (PH : 315 mW)
R-22
SB-41 (PH : 120 mW)
SP-41 (PH : 400 mW)
R-134a
SB-42 (PH : 120 mW)
SP-42 (PH : 400 mW)
Carbon monoxide
SB-50 (PH : 120 mW - max.)
Organic solvents
Freon
Toxic gases
30-39
40-49
50-59
Detection gas
SB series
SB-500 (PH : 120 mW - max.)
Hydrogen sulphide
Ammonia
Oxidizing gases
60-69
Indoor Air Quality
controls (air
purifiers/
ventilation control
systems)
Air Damper control
in automobiles
Notes
MW
AQ
SB-53 under study
Ozone
Nitrogen oxides
Cooking controls
SP-51 under study
SP-53 (PH : 315 mW)
SP-61 under study
SB-62 under study
Chlorine
SP-65 under study
General purpose
SP-MW0 (PH : 400 mW)
Humidity
SP-MW1 (PH : 400 mW)
Alcohol
SP-MW2 under development
Combustion gas
SP-MW3 under development
General purpose
SB-AQ1A (PH : 120 mW)
SP-AQ1/SP-AQ2 (PH : 315 mW)
SP3-AQ2/SP3-AQ2Y (PH : 315 mW)
AD
Cigarette smoke
SB-AQ4 (PH : 140 mW)
SP-AQ3 (PH : 315 mW)
CO2
SB6-AQ6 under development
SP6-AQ6
Gasoline exhaust
gas
SB-AD1 under development
SP-AD1/SP-AD3 under development
Diesel exhaust gas
SB-AD2 under development
SP-AD2/SP-AD3 under development
• Using a Dynamic Driving method in
the heater operation (pulse voltage),
the average heater current can be
reduced to 25 mA (example with 5
V)
• Variation of heater voltage is available
(Standard: 5 V, option-1:12 V and
option-2: 24 V)
* Pre-classified version is available for
the SP-11
3
PRODUCTS REVIEW
SB series
General
Heater coil
The SB series achieves a dramatic reduction of power
consumption in semiconductor gas sensor applications.
Compared with conventional gas sensors, only 15% of
Gas sensitive
semiconductor
the power is required to detect methane, propane or
Lead wire
0.5 mm
other gases. Using this design, increased sensitivity and
improved cross sensitivity in flammable gas detection, CO
0.3 mm
or solvents detection with quick response are achieved.
Structure
Fig 1. Sensing element
The sensing element is a mini bead type semiconductor
mainly composed of tin-dioxide (SnO2). A heater coil and
an electrode wire are embedded in the element (Fig 1). The
100 mesh
SUS 316 gauze (double)
element is installed in the metal housing which uses
Sensing element
Metal housing
(Nickel plated brass)
double stainless steel mesh (100 mesh) in the path of gas
flow. The mesh is an anti-explosion feature (Fig 2). The
Plastic base
sensor has 3 pins for output signal and heater power
Electrode pins
supply. The small sensor reduces the required space and
the size of products. The SB-50 uses an active charcoal
filter as shown in Fig 6.
Fig 2. Structure: standard housing
Operating conditions
Fig 3a and Fig 3b indicate the pin layout and equivalent
circuit and Fig 4 shows the standard circuit of the SB
2
(side view)
series. The applied heater voltage regulates the sensing
RS
element temperature to obtain the specific performance
RH
of sensors. The change in the sensor resistance is generally
fixed or variable load resistor (RL) in series with the sensor
resistance (RS).
3
1
obtained as the change of the output voltage across the
1
2
3
identification mark
Fig 3a. Pin layout
Fig 3b. Equivalent circuit
Note: In this circuit, Pin No.1 with indication mark (Fig 3a)
should be used as a ‘common terminal’ for both heater
VC : Circuit Voltage
VH : Heater Voltage
RL : Load Resistance
voltage (VH) and circuit voltage (VC).
RH : Heater Resistance
VRL: Voltage across load resistance
+
RL
Standard operating conditions:
VC: Less than 5 V DC
RL: Variable (> 750 W )
VH: 900 mV (SB-11, SB-31, SB-AQ1)
1000 mV (SB-AQ4)
900 mV-3 sec / 200 mV-7 sec (SB-50)
Remarks:
Polarity of VC and VH is important.
Apply the VC and VH as shown in the circuit diagram.
4
VC
+
VH
Fig 4. Standard circuit
3
2
RH
1
RS
VRL
PRODUCTS REVIEW
SB series
Dimensions
Fig 5 shows the dimensions of the SB series (standard
Stainless steel mesh
4.5
housing).
Configurations
Fig 6 shows the configurations of the SB series: standard
7.6
Other housing
Lead wire
Sensor cover
2.0
Heater coil
Sensing element
8.4
housing and SB-50 with active charcoal filter.
Special sensor housing with an external sintered metal
Plastic moulding
5.0
cover is available (example: FIg 7).
Electrode pin
1.0
1.5
Sensitivity characteristics
(typical data)
0.25
2.54 2.54
The sensitivity characteristics of semiconductor gas sensors
are shown by the relationship between the sensors
resistance (RS) and concentration of gases. The sensor
0.8
0.8
0.8
resistance decreases with an increase of the gas
Scale: mm
concentration based on a logarithmic function (see page
14 for details of sensing mechanism). The standard test
Fig 5. Dimensions: standard housing
conditions of each model are calibrated to meet a typical
target gas and concentration. For example, methane 1000
ppm for flammable gas detection, hydrogen 100 ppm for
Standard
SB-50 (with active charcoal filter)
100 mesh
SUS 316 gauze
hydrogen detection or ethanol 300 ppm for solvents
Active charcoal
detection. If different conditions are required for other
Metal housing
(Nickel plated brass)
specific gas detection, please consult FIS.
Plastic housing
Electrode pins
Figs 8 to 13 on the next page show the typical sensitivity
characteristics data of SB series gas sensors. In these
Fig 6. Configurations: standard housing and SB-50
diagrams, the sensor resistance change is normalized by
the RS at specific conditions.
Sintered metal
cover
15.0
23.0
Sensor
Holder
PC board
Potting
compound
Lead wire
11.2
Fig 7. SB series with sintered metal housing
5
PRODUCTS REVIEW
SB series
100
RS / RS (ethanol 300 ppm)
RS / RS (at iso-butane 1000 ppm)
10
1
0.1
air level
methane
iso-butane
hydrogen
ethanol
10
1
0.1
0.01
0.01
10
100
1000
Gas concentration (ppm)
10000
1
Fig 8. SB-11A for Hydrocarbons
100
1000
10
100
1
air level
methane
hydrogen
ethanol
0.1
100
1000
Gas concentration (ppm)
10000
10
1
CO
hydrogen
ethanol
CO
0.1
0.01
1
10
100
1000
Gas concentration (ppm)
1
10000
Fig 10. SB-19 for Hydrogen
10
100
1000
Gas concentration (ppm)
10000
Fig 11. SB-50 for CO
1
RS / RS (in air)
RS / RS (in air)
1
air level
methane
hydrogen
ethanol
0.1
0.1
air level
hydrogen
ethanol
CO
1
10
Gas concentration (ppm)
100
Fig 12. SB-AQ1 for Air Quality Controls (general)
6
10
Fig 9. SB-31 for Solvents
RS / RS (CO 100 ppm)
RS / RS (hydrogen 100 ppm)
air level
methane
iso-butane
hydrogen
ethanol
CO
1
10
Gas concentration (ppm)
Fig 13. SB-AQ4 for Air Quality Controls (smoke)
100
PRODUCTS REVIEW
New developments: SB series
1000
SB-95: CO/methane sensor
Using both high and low sensor temperature in the
periodic temperature change method (same operation
Air
100
method as the SB-50), it is possible to detect both CO and
Methane 1000 ppm
RS (kW )
methane selectively with single element.
Fig 14 shows a typical temperature dependency
10
characteristic of the SB-95. When the sensor is operated
with high/low periodic operation (Fig 15), sensor signal
1
CO 1000 ppm
changes according to the temperature dependency
characteristics. By detecting the sensor signal at sufficient
HIGH
LOW
timings (at a high temperature for methane and at a low
0.1
100
temperature for CO), selective detection of both methane
200
300
Sensor temperature (ºC)
400
500
Fig 14. SB-95: Temperature dependency characteristics
and CO has been achieved. Figs 16 and 17 show the
sensitivity characteristics of the SB-95, at high temperature
Using this concept, development of CO or methane, or
both CO and methane detectors can be developed using
the same sensor and circuit.
Heater voltage
and at low temperature signals respectively.
High
0.9 V
Low
0.2 V
5 sec 10 sec
in CO or methane
Sensor output (VRL)
in air
in air
in methane
in CO
Detection point:
high
low
Time
Fig 15. SB-95: Operating conditions and output signal
20
100
10
RS / RS (CO 100 ppm)
RS / RS (at methane 1000 ppm)
10
5
2
1
1
air level
0.1
methane
0.5
CO
CO
hydrogen
hydrogen
ethanol
0.2
0.01
100
1000
10000
Gas concentration (ppm)
Fig 16. SB-95: Sensitivity at HIGH signal for methane
1
10
100
1000
Gas concentration (ppm)
10000
Fig 17. SB-95: Sensitivity at LOW signal for CO
7
PRODUCTS REVIEW
SP series
General
Alumina
substrate
The SP series was developed using an advanced thick film
Sensing
material
Heater
small and thin ceramic substrate, a 50% reduction in
2 mm
printing technology. By applying this technology on a
Lead wires
current and power is achieved. Combinations of new
design, variations of sensing materials and excellent
2 mm
performance and a wide variation in the product range.
Electrodes
0.3 mm
controllability have lead to improvements in sensor
Fig 18. Sensing element
100 mesh
SUS 316 gauze
(double)
Structure
The sensing material is formed on the alumina substrate
Plastic housing
on which the gold electrodes are printed. A thick film
Sensing element
Plastic base
Electrode and
heater pins
heater of ruthenium-oxide or platinum is printed on the
reverse of the substrate (Fig 18).
The element is installed in the plastic or mesh type
housing which uses a double stainless steel mesh (100
Fig 19. Structure: standard type (P1)
mesh) in the path of gas flow (Fig 19: standard type).
The sensor has four pins for output signal and heater
(Top view)
5
power supply and one free pin for identification.
1
4
RS
Operating conditions
3
2
3
2
Fig 20a indicates the pin layout and Fig 20b shows the
2
3
shown in Fig 21.
The applied heater voltage regulates the sensing element
RH
(Bottom view)
equivalent circuit. The standard circuit for the SP series is
4
1
1
4
temperature to obtain the specific performance of
sensors. As in the SB series, the change in sensor
resistance is obtained from the change in the output
5
Fig 20a. Pin layout
Fig 20b. Equivalent circuit
voltage across the fixed or variable load resistor (RL).
4
VH
VC
RH
RS
1
RL
Standard operating conditions:
VC: 24 V max (DC/AC)
VH: 5.0 V ± 4% (DC/AC)
RL: Variable (PS < 15 mW)
PS = ( VC - VRL )2/RS
8
3
Fig 21. Standard circuit
Remarks:
Polarity of the circuit voltage (VC) is not important.
2
VRL
PRODUCTS REVIEW
SP series
Dimensions
Fig 22 shows the dimensions of the SP series (standard
housing).
Stainless steel mesh
Configurations: variation of housing design
Lead wire
Sensing element
Fig 23 shows the variation of the SP (5 pin) configuration.
Other variations of sensor pin layout and housing designs
17.0
are available.
16.5
b) SP4 type base (4 pin) with compact plastic
housing
Stainless steel mesh
Sensing element
Lead wire
Plastic housing
Plastic base
6.5
• Fig 24: a) SP3 type base (3 pin) with compact plastic
housing
Nickel pin
• Fig 25: Metal base (TO-39 type 4 pin)
9.5
1.0
• Fig 26: Metal base with a sintered metal external
housing
Sensitivity characteristics
(typical data)
45
45
Figs 27 to 38 on the following pages show the typical
Scale: mm
sensitivity characteristics data of SP series gas sensors. In
Fig 22. Dimensions: standard housing
these diagrams, the change in sensor resistance is
normalized by the RS at specific conditions.
Plastic type (P1)
Mesh type (MC/MP)
Fig 23. Configuration of sensor housing
Sintered metal
cover
12.0
14.0
11.5
12.0
15.0
Scale: mm
23.0
Sensor
Holder
Fig 24. Compact plastic housing: SP3 (left) and SP4 (right)
PC board
Potting
compound
Lead wire
11.2
Fig 26. Sintered metal housing with metal base
Fig 25. Metal base (TO-39 type 4 pin)
9
PRODUCTS REVIEW
SP series
10
RS / RS (at methane 3000 ppm)
RS / RS (at iso-butane 1000 ppm)
10
1
air level
methane
propane
iso-butane
hydrogen
ethanol
1
air level
methane
iso-butane
CO
hydrogen
ethanol
0.1
0.1
100
1000
Gas concentration (ppm)
10000
100
Fig 27. SP-11 for Hydrocarbons
100
RRS / RS (at Hydrogen 100 ppm)
RS / RS (at iso-butane 1500 ppm)
1
air level
methane
iso-butane
CO
10
1
air level
methane
hydrogen
ethanol
CO
0.1
hydrogen
ethanol
0.01
0.1
100
1000
Gas concentration (ppm)
1
10000
100
1000
10000
Fig 30. SP-19 for Hydrogen
10
10
1
RS / RS (in air)
100
1
air level
methane
iso-butane
hydrogen
ethanol
CO
0.1
10
Gas concentration (ppm)
Fig 29. SP-15A for Propane/butane (LP-Gas)
RS / RS (at ethanol 100 ppm)
10000
Fig 28. SP-12A for Methane (Natural gas)
10
0.1
air level
methane
iso-butane
hydrogen
ethanol
CO
0.01
0.01
0.001
1
10
100
1000
Gas concentration (ppm)
Fig 31. SP-31 for Solvents
10
1000
Gas concentration (ppm)
10000
1
10
100
1000
Gas concentration (ppm)
Fig 32. SP-32 for Alcohol
10000
PRODUCTS REVIEW
SP series
10
RS / RS (at R-134a 100 ppm)
RS / RS (at R-22 100 ppm)
10
1
air level
methane
iso-butane
R-22
ethanol
R-134a
0.1
0.01
10
100
1000
Gas concentration (ppm)
10000
1
air level
methane
iso-butane
R-22
ethanol
R-134a
0.1
0.01
10
Fig 33. SP-41 for Freon (R-22)
100
1000
Gas concentration (ppm)
10000
Fig 34. SP-42 for Freon (R-134a)
10
RS / RS (at 11.75 g/m3)
RS / RS (at ammonia 100 ppm)
1
0.1
air level
ammonia
H2S
hydrogen
ethanol
CO
0.01
1
humidity
0.1
1
10
100
Gas concentration (ppm)
1
1000
Fig 35. SP-53 for Ammonia
1
1
RS / RS (in air)
10
RS / RS (in air)
100
Fig 36. SP-MW1 for Cooking Controls (general)
10
air level
H2S
hydrogen
ammonia
ethanol
CO
0.1
10
Absolute Humidity (g/m3)
0.1
air level
hydrogen
ethanol
0.01
0.01
0.1
1
10
Gas concentration (ppm)
Fig 37. SP-AQ2 for Indoor Air Quality (general)
100
0.1
1
10
Gas concentration (ppm)
100
Fig 38. SP-AQ3 for Indoor Air Quality (smoke)
11
PRODUCTS REVIEW
Related products
Microprocessors: IC- series
15
1
14
8.8 ± 0.2
indoor air quality controls, CO detection,
domestic gas alarms, etc. Application of IC series
0.25 +0.1
-0.05
28
10.16 ± 0.25
(microcomputers) for various applications such as
0-15°
FIS develops specially designed microprocessors
enables efficient and economical solutions in the
development of applied products.
26.1 max
1.0 ± 0.1
1.243TYP
3.0±0.3 3.8±0.3
0.3 min 3.3±0.2
25.6 ± 0.2
0.46 ± 0.1
unit: mm
1.778
Fig 39. Standard compact plastic DIL package
15
9.0 max
11.8 ± 0.3
0.15 ± 0.05
28
1.5 ± 0.4
14
18.9 max
0.43 ± 0.1
1.27 ± 0.05
0.1 ± 0.1
2.5 max
1
unit: mm
Fig 40. Flat package for SMD
Field
CO detection
Model
IC-04-1 (OTP)
IC-04-2.1
(OTP)
IC-04-2.2
(EMC1004:
SMD)
Description
Features and functions
A series of microprocessors for driving the mini SB50 sensor for reliability, low power, quick response
and low cost CO detectors. These microprocessors
include useful functions for CO alarm devices.
Variations of functions and units are available with
different versions. Standard product is the IC-04-2.2.
with SMD type package.
• Heater power supply (Dynamic Driving method), signal
detection (periodic sensor temperature change
operation)
• Alarm functions (including various options)
• Temperature and humidity compensation
• Memory function for calibration
• Fail-safe signal, etc.
A microprocessor for domestic gas alarms for SP
series including various functions which provide high
reliability in flammable gas leak detection.
• Initial delay, alarm delay, temperature compensation,
fail-safe and other functions
OTP: One
Time
Processor
Domestic gas
alarms
IC-05
(EMC6010:
DIP)
(EMC6020:
SMD)
12
PRODUCTS REVIEW
Modules
Evaluation modules: EVM series
The EVM series includes modules with basic operation/detection circuits and/or examples of application circuits using FIS
sensors and microprocessors.
General
purpose
Model
EVM-SB-01:
- SB series
- SB-11 (for
flammable
gas detection)
EVM-SB-07:
- SB series
Description and functions
Dimensions:
Unit: mm, Scale: approx. 1/2
Pre-calibrated module (e.g. at 10% LEL
for flammable gas detection). Includes a
standard driving circuit for evaluating the
SB series gas sensor
•
•
•
•
100
Sensor
22
Field
Compact design
Low power consumption
5 V DC input
VRL output (0 - 4 V)
White
Red
Black
IC
VR
37
Module includes the ‘Dynamic Driving’
operation circuit for the SB series
65
Easy operation
Low power and low current
5 V DC input
VRL output
EVM-SB-07
SB sensor
VR2
50
•
•
•
•
1
2
3
IC1
CN1
VR3
VR1
IC2
EVM-SB-02
- SB-AQ series
+ IC-02
Module includes driving circuit for the
SB-AQ1 or SB-AQ4 and microprocessor
IC-02 using ‘Dynamic Driving’ operation
with low power consumption
• Low power and low current
• LED’s indication and control signals
for a fan (3 levels)
• 12 V DC input (9 V battery operation
is also possible)
• Pre-calibrated
• Auto/manual switch and a timer
function
90
SB-AQ
VR
Buzzer
X1
90
Air quality
controls
(air
purifiers)
VR
VR
IC-02.2
12 V
VR
GND
LED
SW
Module for evaluating the mini CO
sensor SB-50 with microprocessor IC-04.
Periodic sensor temperature change
operation with 10 seconds cycle (High: 3
secs and Low: 7 secs). Low current
consumption using a ‘Dynamic Driving’
operation method
Thermistor
X1
SB-50
IC-04
Buzzer
V G
LED
VR
Condenser
ZNR
-
LED
Terminal
• Mains power operation with no
transformer (220 V and 100 V
versions)
• Low power consumption of 60 mW.
• Visual alarm, buzzer and output
signals (alarm and sensor signal
output)
95
AC AC +
EVM-SB-05
- SB-50 + IC-04
70
CO
detection
13
PRODUCTS REVIEW
Modules
Example of applied products
Examples of commercial application designs are also available such as EVM-SB-08 and DGA-ES.
Field
CO
detection
Model
EVM-SB-08
- SB-50 + IC-04
Description and functions
Dimensions:
Module for general purpose using the
SB-50 with microprocessor IC-04.
80
• Compact design
• 5 V DC input
• 2 level alarm signal output (for
remote alarm), initial delay, fail-safe
and other functions
DGA-ES:
- SP-12A/SP-15
+ IC-05
LED
Sensor
CN1
30
TH
VR
An example of domestic gas alarm (for
natural gas or LP-Gas) using the SP-12A/
SP-15 and IC-05
• Power supply: 100 V, 220 V AC or
other conditions
• With functions such as initial delay,
alarm delay, temperature
compensation, etc.
• Natural gas (methane) and propane
versions
X1
SB-50
124
X1
LED1
ZNR1
IC
-05
LED2
Transformer
62
Flammable
gas
detection
Unit: mm, Scale: approx. 1/2
LED3
CN
TH1
CN1
Sensor
VR
Relay
Terminal block
Buzzer
Pre-calibrated modules: PCM series
Combinations of sensors and small PCBs including fixed and variable resistors (RL). These modules are calibrated at suitable
conditions for indoor air quality or other applications and avoid calibration process in the assembly of applied products.
Air quality
controls
Model
PCM-SP/ST-01
- SP-AQ series
- ST-AQ series
Description and functions
Dimensions:
Unit: mm, Scale: approx. 1/2
Pre-adjusted sensor module for air quality
controls
100
• Sensor + PCB + cable
• 5 V DC input
• Output signal is specified by the
sensitivity to hydrogen
White
Red
Black
22
Field
VR
1
2
3
37
PCM-SP-02
- SP-12A/SP-15
Pre-adjusted sensor module for methane
or LP-Gas detection with temperature
compensation
• Sensor + PCB + terminal
• 5 V DC input
• Output signal is specified by the
sensitivity to methane /LP-Gas
40
TH
23
Flammable
gas
detection
R
VR
Pre-classified sensor: PC version
Pre-classified sensors are supplied with code numbers showing sensor resistance level at specified conditions. Using this
version, specific levels of output signal (VRL) are obtained in the applied products. See SP-11/SP-12 User’s Manual for details.
14
PRODUCTS REVIEW
Metal oxide (SnO2) semiconductor gas sensor
The conductivity of Tin dioxide (SnO2) metal oxide semiconductor materials changes according to gas concentration changes.
This is caused by adsorption/desorption of oxygen and reaction between surface oxygen and gases. These reactions cause a
dynamic change of electric potential on SnO2 crystal and results in the decrease of sensor resistance under the presence of
reducing gases such as CO, methane, hydrogen. The figures below indicate the sensing mechanism of the SnO 2 gas sensor.
(Sensing element)
(Sensor unit)
Sensing material
Sensing element
2 mm
SnO2 particles:
sub-micron to several ten micron
Microscopic image of
SnO2 particles
(secondary particles)
(In the presence of CO)
O2- + CO ➔ CO2 + eO - + CO ➔ CO2 + eO2- + CO ➔ CO2 + 2e-
O2
O2-
e-
e-
O2-
Grain boundary
O2-
e-SnO2-X e
e- e
O2O2
O2-
e- e-
e-
e-
O2-
O2-
O2-
e- SnO2-X ee- e- e-
O2-
O2O2
O2O2O2
O2-
-
e
e-
e-
e-
SnO2-X
e- e
O2-
e-
e- e e
(several hundred
angstrom Å)
O2-
e-
e-
SnO2-X e-
SnO2 crystals
e-
e-
e-
CO
O2
O2
O2 +
e-
e-
e-
O2-
ee-
ee- eSnO2-X
e- - ee
e
e
eO2-
e-
e-
ee-
e-
SnO2-X
e- e
O2-
e-
e-
O2
O2- ➔ O2 + e-
O2e- O -
O - ➔ 1/2O2 + e-
1/2O2 + ➔
1/2O2 + 2e- ➔ O 2-
e-
ee-
e-
CO
e- ➔
Potential barrier changes
e- e-
e-
e-
O2-
O2
CO
O2-
O2-
O2-
O2- ➔ O2 + eO - ➔ 1/2O2 + eO 2- ➔ 1/2O2 + 2e-
O2 + e- ➔ O21/2O2 + e- ➔ O 1/2O2 + 2e- ➔ O 2-
O2
CO
O2
O 2- ➔ 1/2O2 + 2e-
e-
e-
e-
e-
e-
in air
In the presence of CO
Low conductivity (high resistance)
High conductivity (low resistance)
e-
(kW )
100
Sensor Resistance (log scale)
Sensor resistance
in air is kept at high level:
e.g. > 100 kW .
In the presence of reducing gases,
sensor resistance decreases with
increase of gas concentration.
air level
10
Reducing gas
1
10
100
1000 (ppm)
Gas concentration (log scale)
15
FIS INC.
2-5-26, HACHIZUKA,
IKEDA, OSAKA.
563 JAPAN
TEL: +81-727-61-5886
FAX: +81-727-61-5876
CONTACT:
In the interest of continued product improvement we reserve the right to change design features without prior notice
revised June, 1998. Version 4.2