HANWEI ELECTRONICS CO.,LTD
TECHNICAL DATA
MQ-138
http://www.hwsensor.com
MQ-138 GAS SENSOR
FEATURES
Wide detecting scope
Fast response and High sensitivity
Stable and long life
Simple drive circuit
APPLICATION
They are used in Breath alcohol detector, solvent detectors ,Air quality control equipments for
buildings/offices, are suitable for detecting of n-Hexane, Benzene, NH3, alcohol, ,smoke, CO ,etc.
SPECIFICATIONS
A. Standard work condition
Symbol Vc VH
Parameter name Circuit voltage Heating voltage
Technical condition 5V±0.1 5V±0.1
Remarks AC OR DC ACOR DC
RL Load resistance RH Heater resistance
can adjust 31Ω±3Ω
Room Tem
PH Heating consumption less than 850mw
B. Environment condition
Symbol
Parameter name
Technical condition
Remarks
Tao Using Tem
-10℃-45℃
Tas Storage Tem
-20℃-70℃
RH Related humidity
less than 95%Rh
O2
Oxygen concentration
21%(standard condition)Oxygen minimum value is
concentration can affect
over 2%
sensitivity
C. Sensitivity characteristic
Symbol
Parameter name
Technical parameter
Remarks
Rs Sensing Resistance
20KΩ-200KΩ
(1000ppm Benzene )
Detecting concentration scope:
10ppm-1000ppm
α (200/50)
Concentration Slope rate
≤0.65
Benzene
10ppm-1000ppm
NH3 Standard Detecting Condition
Temp: 20℃±2℃ Vc:5V±0.1 Humidity: 65%±5% Vh: 5V±0.1
Alcohol 10ppm-3000ppm NH3
Preheat time
Over 24 hours
D. Structure and configuration, basic measuring circuit
Parts 1 Gas sensing
layer 2 Electrode 3 Electrode line 4 Heater coil 5 Tubular ceramic 6 Anti-explosion
network 7 Clamp ring 8 Resin base 9 Tube Pin
Materials SnO2
Au Pt Ni-Cr alloy Al2O3 Stainless steel gauze (SUS316 100-mesh) Copper plating Ni Bakelite Copper plating Ni
Configuration A
Fig. 1
Configuration B
Fig.2
A A
Structure and configuration of MQ-138 gas sensor is shown as Fig. 1 (Configuration A or B), sensor composed by micro AL2O3 ceramic tube, Tin Dioxide (SnO2) sensitive layer, measuring electrode and
TEL: 86-371-67169070 67169080
FAX: 86-371-67169090
E-mail:
[email protected]
HANWEI ELECTRONICS CO.,LTD
MQ-138
http://www.hwsensor.com
heater are fixed into a crust made by plastic and stainless steel net. The heater provides necessary
work conditions for work of sensitive components. The enveloped MQ-138 have 6 pin ,4 of them are
used to fetch signals, and other 2 are used for providing heating current.
Electric parameter measurement circuit is shown as Fig.2
E. Sensitivity characteristic curve
Fig.2 sensitivity characteristics of the MQ-138
10
MQ138
Benzene n-Hexane
Fig.3 is shows the typical sensitivity characteristics of
the MQ-138 for several gases.
CH4 in their: Temp: 20℃、
CO Humidity: 65%、
alcohol propane
O2 concentration 21% RL=20kΩ
Air Ro: sensor resistance at 1000ppm of
Benzene in the clean air.
Rs :sensor resistance at various 1 concentrations of gases.
Rs/Ro Rs/Ro
0.1 100
1000
ppm
10000
1.8
1.6 1.4
Fig.4 is shows the typical dependence of 33%RH the MQ-138 on temperature and humidity.
1.2 85%RH Ro: sensor resistance at 1000ppm of Benzene in
1 air
0.8 at 33%RH and 20 degree. 0.6 Rs: sensor resistance at 1000ppm of Benzene 0.4 at different temperatures and humidity
0.2 degree
0 Fig.4
-20 -10 0 10 20 30 40 50 60
SENSITVITY ADJUSTMENT .Resistance value of MQ-138 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 100ppm Benzene or Alcohol concentration in air and use value of Load resistance that( RL) about 47 KΩ(20KΩ to 100 KΩ).
When accurately measuring, the proper alarm point for the gas detector should be determined after considering the temperature and humidity influence.
TEL: 86-371-67169070 67169080
FAX: 86-371-67169090
E-mail:
[email protected]
.