Toxic Gas Sensor
（Model：MQ-7）
Manual
Version: 1.3
Valid from: 2014-05-01
Zhengzhou Winsen Electronics Technology Co., Ltd
Statement
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written permission, any part of this manual shall not be copied, translated, stored in database or
retrieval system, also can’t spread through electronic, copying, record ways.
Thanks for purchasing our product. In order to let customers use it better and reduce the faults
caused by misuse, please read the manual carefully and operate it correctly in accordance with the
instructions. If users disobey the terms or remove, disassemble, change the components inside of
the sensor, we shall not be responsible for the loss.
The specific such as color, appearance, sizes &etc, please in kind prevail.
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right to improve the products without notice. Please confirm it is the valid version before using this
manual. At the same time,
users’ comments on
optimized using way are welcome.
Please keep the manual properly, in order to get help if you have questions during the usage in the
future.
Zhengzhou Winsen Electronics Technology CO., LTD
Zhengzhou Winsen Electronics Technology Co., Ltd
www.winsensor.com
MQ-7 Semiconductor Sensor for Carbon Monoxide
Profile
Sensitive material of MQ-7 gas sensor is SnO
2,
which
with lower conductivity in clean air. It make detection
by method of cycle high and low temperature, and
detect CO at low temperature(heated by 1.5V).The
sensor’s conductivity gets higher along with the CO
gas concentration rising. At high temperature(heated
by 5.0V),it cleans the other gases adsorbed at low
temperature. Users can convert the change of
conductivity to correspond output signal of gas
concentration through a simple circuit.
Features
It has good sensitivity to carbon monoxide in wide range, and has advantages such as long lifespan, low
cost and simple drive circuit &etc.
Main Applications
It is widely used in domestic CO gas leakage alarm, industrial CO gas alarm and portable CO gas detector.
Technical Parameters
Model
Sensor Type
Standard Encapsulation
Target Gas
Detection range
Loop Voltage
Heater Voltage
V
c
V
H
T
L
R
L
R
H
P
H
S
Vs
α
Stable.1
MQ-7
Semiconductor
Plastic cap
carbon monoxide
10½500ppm CO
≤10V DC
5.0V±0.1V AC or DC（High tem.）
1.5V±0.1V AC or DC（Low tem.）
60 S±1S（High tem.）
，
90 S±1S（Low tem.）
Adjustable
29Ω±3Ω（room tem.）
≤900mW
Rs(in air)/Rs(in 150ppm CO)≥5
2.5V½4.3V (in 150ppm CO)
≤0.6(R
300ppm
/R
50ppm
CO)
20℃±2℃；55%±5%RH
Vc:5.0V±0.1V；
Standard Circuit
Conditions
Heater Time
Load Resistance
Heater Resistance
Sensor character
under standard
test conditions
Heater consumption
Sensitivity
Output Voltage
Concentration Slope
Tem.
Humidity
Standard test
conditions
Standard test circuit
V
H
（High
tem.） 5.0V±0.1V；
：
V
H
（Low
tem.） 1.5V±0.1V
：
Fig1.Sensor S
tructure
Unit: mm
Preheat time
Over 48 hours
NOTE: Output voltage (Vs) is V
RL
in test environment.
Tel: 86-371-67169097/67169670
Fax: 86-371-60932988
Email:
sales@winsensor.com
Zhengzhou Winsen Electronics Technology Co., Ltd
www.winsensor.com
Basic Circuit
V
H
AC or DC
High voltage and
low voltage
can switch
Fig2. MQ-7 Test Circuit
Instructions:
The above fig is the basic test circuit of MQ-7.The sensor requires two voltage inputs: heater
voltage (V
H
) and circuit voltage(V
C
). V
H
is used to supply standard working temperature to the sensor and it
can adopt DC or AC power. For this model sensor, V
H
should be at 1.5V±0.1V low voltage when detect CO
while should be at 5V±0.1V at non detection status(resuming period). V
RL
is the voltage of load
resistance R
L
which is in series with sensor. Vc supplies the detect voltage to load resistance R
L
and it
should adopts DC power.
Description of Sensor Characters
CO
Air
CH
4
H
2
Fig3.Typical Sensitivity Curve
The ordinate is resistance ratio of the sensor (Rs/R
0
), the
abscissa is concentration of gases. Rs means resistance in
target gas with different concentration, R
0
means
resistance of sensor in clean air. All tests are finished
under standard test conditions.
Fig4.Typical temperature/humidity characteristics
The ordinate is resistance ratio of the sensor (Rs/Rso).Rs
means resistance of sensor in 150ppm CO gas under different
tem. and humidity. Rso means resistance of the sensor in
150ppm CO gas under 20℃/55%RH.
Tel: 86-371-67169097/67169670
Fax: 86-371-60932988
Email:
sales@winsensor.com
Zhengzhou Winsen Electronics Technology Co., Ltd
www.winsensor.com
150ppm CO gas (RL=4.7k)
Time(s)
Fig5.Sensitity Curve
Fig5 shows the V
RL
in CO gas with different concentration.
The resistance load R
L
is 4.7 KΩ and the test is finished in
standard test conditions.
Fig6.Responce and Resume
Fig5 shows the changing of V
RL
in the process of putting
the sensor into target gas and removing it out.
150ppm CO gas (RL=4.7k)
Time(day)
Fig7.long-term Stability
Test is finished in standard test conditions, the abscissa is observing time and the ordinate is V
RL
.
Cautions
1 .Following conditions must be prohibited
1.1 Exposed to organic silicon steam
Sensing material will lose sensitivity and never recover if the sensor absorbs organic silicon steam.
Sensors must avoid exposing to silicon bond, fixature, silicon latex, putty or plastic contain silicon
environment.
1.2 High Corrosive gas
If the sensors are exposed to high concentration corrosive gas (such as H
2
S, SO
X
, Cl
2
, HCl etc.), it will
not only result in corrosion of sensors structure, also it cause sincere sensitivity attenuation.
1.3 Alkali, Alkali metals salt, halogen pollution
The sensors performance will be changed badly if sensors be sprayed polluted by alkali metals salt
Tel: 86-371-67169097/67169670
Fax: 86-371-60932988
Email:
sales@winsensor.com
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