Week 9 of FYP 2

Date : 08/04/2014 (Tuesday)

Title : MQ-4 Semiconductor Sensor for Natural Gas

Description:

          Sensitive material of MQ-4 gas sensor is SnO2, which with lower conductivity in clean air. When the target combustible gas exist, the sensor’s conductivity is higher along with the gas concentration rising. Please use simple electro circuit, Convert change of conductivity to correspond output signal of gas concentration.

MQ-4 gas sensor has high sensitivity to Methane, also to Propane and Butane. The sensor could be used to detect different combustible gas, especially Methane; it is with low cost and suitable for different application.

Character: 

• ·         Good sensitivity to Combustible gas in wide range.
• ·         High sensitivity to LPG, Propane and Hydrogen.
• ·         Long Life and Low Cost.
• ·         Simple drive circuit.

Application:

• ·         Domestic gas leakage detector.
• ·         Industrial Combustible gas sensor.
• ·         Portable gas sensor.

Configuration:

Sensor Pin Configuration

Technical Data:

Sensor Technical Data

Basic Test Loop:

Sensors Basic Test Loop

The above is basic test circuit of the sensor. The sensor needs to be put two voltage, heater voltage (VH) and test voltage (VC). VH used to supply certified working temperature to the sensor, while VC used to detect voltage (VRL) on load resistance (RL) whom is in series with sensor. The sensor has light polarity, Vc need DC power. VC and VH could use same power circuit with precondition to assure performance of sensor. In order to make the sensor with better performance, suitable RL value is needed:

Power of Sensitivity body (Ps):

Resistance of sensor (Rs):

Sensitivity Characteristics:

Sensors Sensitivity Characteristics

Fig.1 shows the typical sensitivity characteristics of the MQ-4, ordinate means resistance ratio of the sensor (Rs/Ro ), abscissa is concentration of gases. Rs mean resistance in different gases, Ro means resistance of sensor in 1000ppm Methane. All tests are under standard test conditions.

P.S.: Sensitivity to smoke is igniting 10pcs cigarettes in 8m3  rooms, and the output equals to 200ppm Methane.

Influence of Temperature/Humidity:

Sensors Temperature/Humidity Influences

Fig.2 shows the typical temperature and humidity characteristics. Ordinate means resistance ratio of the sensor (Rs/Ro ), Rs means resistance of sensor in 1000ppm Methane under different temperature and humidity., Ro means resistance of the sensor in environment of 1000ppm Methane, 20˚C/65%RH

Structure and Configuration: 

Sensors Structure and Configuration

Structure and configuration of MQ-4 gas sensor is shown as Fig. 3, sensor composed by micro AL2O3 ceramic tube, Tin Dioxide (SnO2) sensitive layer, measuring electrode and 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-4 has 6 pin, 4 of them are used to fetch signals, and other 2 are used for providing heating current.