GAS SENSOR :

The sensing element of gas sensors is a tin dioxide (SnO2) semiconductor which has low conductivity in clean air. In the presence of a detectable gas, the sensor's conductivity increases depending on the gas concentration in the air. A simple electrical circuit can convert the change in conductivity to an output signal which corresponds to the gas concentration.

It has high sensitivity to methane, propane, and butane, making it ideal for natural gas and LPG monitoring. The sensor can detect a wide range of gases, making it an excellent, low cost sensor for a wide variety of applications. Also available with a ceramic base which is highly resistant to severe environments up to 200°C

Features:

• General purpose sensor with sensitivity to a wide range of combustible gases
• High sensitivity to methane, propane, and butane
• Long life and low cost
• Uses simple electrical circuit

The figure below represents typical sensitivity characteristics, all data having been gathered at standard test conditions. The Y-axis is indicated as sensor resistance ratio (Rs/Ro) which is defined as follows:

Rs = Sensor resistance of displayed gases at various concentrations

Ro = Sensor resistance in 1000ppm methane

The figure below represents typical temperature and humidity dependency characteristics. Again, the Y-axis is indicated as sensor resistance ratio (Rs/Ro), defined as follows:

Rs = Sensor resistance at 1000ppm of methane at various temperatures/humidities

Ro = Sensor resistance at 1000ppm of methane at 20°C and 65% R.H.

Pin Connection and Basic Measuring Circuit:

The numbers shown around the sensor symbol in the circuit diagram at the right Correspond with the pin numbers shown in the sensor's structure drawing (above).When the sensor is connected as shown in the basic circuit, output across the Load Resistor (VRL) increases as the sensor's resistance (Rs) decreases, depending on gas concentration.

Applications:

• Domestic gas leak detectors and alarms
• Portable gas detectors

Carbon monoxide gas:

This Carbon Monoxide (CO) gas sensor detects the concentrations of CO in the air and outputs its reading as an analog voltage. The sensor can measure concentrations of 10 to 10,000 ppm.The sensor can operate at temperatures from -10 to 50°C and consumes less than 150 mA at 5 V. Please read the MQ7 datasheet (185k pdf) for more information about the sensor.

 Circuit Diagram of Carbon Monoxide

Connections:

Connecting five volts across the heating (H) pins keeps the sensor hot enough to function correctly. Connecting five volts at either the A or B pins causes the sensor to emit an analog voltage on the other pins. A resistive load between the output pins and ground sets the sensitivity of the detector. The resistive load should be calibrated for your particular application using the equations in the datasheet, but a good starting value for the resistor is 10 kΩ.

Features:

·         High sensitivity (MQ-7 sensor)

·         Detection range: 20-2000ppm CO

·         Response time: <150s

·         Heater voltage: 5.0v

·         Dimensions: 16mm

Co₂ Gas concentration module:

Complete and ready-to-run carbon dioxide concentration module for outputting the CO₂ concentration in digital format to microcontrollers or computer systems. The unit can measure co₂ concentration from 0 to 10,000_ppm, with concentration readings provided as either an analog signal, PWM or digital UART for direct connection to a microcontroller.

No calibration is required and the output is highly accurate to within 50_ppm. Built-in temperature compensation ensures readings are accurate over a wide temperature range. The unit is compact and easy equipment, air conditioning equipment, research projects and much more.

Configuration of CO₂ Gas Sensor

Features:

• Ready-to-run no additional circuit or calibration required
• Highly accurate didital output
• Concentration readings available in either analog, PWM or digital format
• Detection range:0-120,000ppmCo₂ (carbon dioxide)
• Accuracy: ±50ppm
• Dimensions: 57mm Length, 35mm width