Data Sheet

HANWEI ELECTRONICS CO ., LTD MQ –7 http://www.hwsensor.com
TEL:[phone] 67169080 FAX:[phone] Email: [e-mail]
OPERATION PRINCIPLE
. The surface resistance of the sensor Rs is obtained through effected voltage signal output of the
load resistance RL which series-wound. The relationship between them is described:
Rs\RL = (Vc-VRL) / VRL
Fig. 5 shows alterable situation of RL signal output measured by using Fig. 2 circuit output
signal when the sensor is shifted from clean air to carbon monoxide (CO) , output signal
measurement is made within one or two complete heating period (2.5 minute from high voltage
to low voltage ).
Sensitive layer of MQ-7 gas sensitive components is made of SnO2 with stability, So, it has
excellent long term stability. Its service life can reach 5 years under using condition.
SENSITVITY ADJUSTMENT
Resistance value of MQ-7 is difference to various kinds and various concentration gases. So, When
using this components, sensitivity adjustment is very necessary. we recommend that you calibrate the
detector for 200ppm CO in air and use value of Load resistance that( R
L
) about 10 KΩ(5KΩ to 47 KΩ).
When accurately measuring, the proper alarm point for the gas detector should be determined after
considering the temperature and humidity influence. The sensitivity adjusting program:
a. Connect the sensor to the application circuit.
b. Turn on the power, keep preheating through electricity over 48 hours.
c. Adjust the load resistance RL until you get a signal value which is respond to a certain
carbon monoxide concentration at the end point of 90 seconds.
d. Adjust the another load resistance RL until you get a signal value which is respond to a CO
concentration at the end point of 60 seconds .
Supplying special IC solutions, More detailed technical information, please contact us.
In air
In 100ppmCO
60s
VH5v
1.4v
Fig.5
Fig.4 is shows the typical
dependence of the MQ-7 on
temperature and humidity.
Ro: sensor resistance at 100ppm CO in
air at 33%RH and 20degree.
Rs: sensor resistance at 100ppm CO at
different temperatures and humidities.
MQ-7
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
-10 0 10 20 30 40 50
Temp
Rs/Ro
33%RH
85%RH
Fig.4
In air
Signal
90s