Gas Sensor

Gas sensor is intended to determine the composition and concentration of the relevant material via an electrical signal.

Gas detection can be done by two ways.
1. Calorimetric detection, which measure gas concentration vs. temperature rise produced by the heat of reaction on a catalytic surface ;
2. Detection due to the change of electrical parameter, such as the change in electrical conductivity induced by adsorption or reaction of gases on the solid surfaces.

Gas sensor fabrication is done by two ways. The first is directly heated type in which two heater coils are bonded inside the ceramic element itself. These separate heater coils also act as electrodes to detect changes in the conductance of the stannic oxide ceramic. The second is an indirectly heated type in which the single heater coil is separated from the ceramic by a tubular alumina substrate.
Gas sensors are very useful to prevent accidents due to leakages, thus saving lives and equipment.

Detection of different molecules

Detection of hydrogen:
In the case of thick ,dense catalytic metals, hydrogen or hydrogen-containing molecules such as hydrocarbons dissociate on the surface of metal and the resulting hydrogen atoms diffuse through the metal within microseconds to the insulator surface. This occurs at temperatures as low as 150°C, depending on the molecule and increase with temperature.

Detection of Ammonia:
The detection of ammonia requires the use of a porous catalytic metal. To obtain a gas response from the NH3 molecule, it is believed that active sites of “triple points” are required where the molecules are in contact with the metal, insulator, and ambient. The total gas response is a combination of the response at the metal insulator interface,metal in contact with the insulator and exposed insulator surface.

Detection of Hydrocarbon:
The field effect devices with catalytic metal contact respond to hydrogen as well as other hydrogen-containing molecules such as hydrocarbons through delivery of hydrogen atoms or ions to the metal oxide interface when the molecules are dissociate on the catalytic metal surface. However, oxygen molecules also dissociate on the catalytic metal surface and react with the dissociation products from the hydrocarbons to produce water and carbon dioxide, which leave the surface. This process consumes hydrogen and thus decreases the sensor signal, provide opportunity to indirectly detect the presence of oxygen.

Detection of Carbon Monoxide:
The response to hydrocarbons can be explained by the dissociated hydrogen atoms forming a polarized layer at the insulator surface.

Different type of gas sensors

Carbon Dioxide CO2 Sensor
Excellent performance CO2 Sensor, for use in a wide range of applications, including air quality monitoring, smoke alarms, mine and tunnel warning systems, greenhouses, etc. The sensor is easy to use and can be easily incorporated in a small portable unit.
Features
• High Sensitivity
• Detection Range: 0 - 10,000 ppm CO2
• Response Time: <60s
• Heater Voltage: 6.0V

Alcohol Sensor
Alcohol Sensor for use in Breathalyzer’s or in an alarm unit, to detect the presence of alcohol vapors. This sensor unit offers very high sensitivity, combined with a fast response time. The unit will work with a simple drive circuit and offers excellent stability with long life.
Features
• High Sensitivity
• Detection Range: 10 - 1,000 ppm Alcohol
• Fast Response Time: <10s
• Heater Voltage: 5.0V

High-Accuracy Alcohol Sensor
Hot-wire High Accuracy Alcohol Sensor, for use with breathalyzer units. Low power consumption, makes this sensor ideal for battery powered units. Wide operating temperature range with little or no adjustment required for temperature and humidity.
Features
• High Sensitivity
• Detection Range: 0 - 1,000 ppm Alcohol
• Fast Response Time: <20s
• Working Voltage: 3.0V
• Working Current: ~120mA

LPG Sensor
Ideal sensor for use to detect the presence of a dangerous LPG leak in your car or in a service station, storage tank environment. This unit can be easily incorporated into an alarm unit, to sound an alarm or give a visual indication of the LPG concentration. The sensor has excellent sensitivity combined with a quick response time. The sensor can also sense iso-butane, propane, LNG and cigarette smoke.
Features
• High Sensitivity
• Detection Range: 100 - 10,000 ppm iso-butane propane
• Fast Response Time: <10s
• Heater Voltage: 5.0V

Carbon Monoxide (CO) Sensor
Carbon Monoxide sensor for use in industrial applications. This unit offers excellent long life performance with stable sensing characteristics.
Features
• High Sensitivity
• Detection Range: 10 - 1,000 ppm CO
• Response Time: <150s
• Heater Voltage: 5.0V

Natural Gas Sensor
Detect dangerous gas leaks in the kitchen or near the gas heater. This unit detects 300 to 5000ppm of Natural Gas. Ideal to detect dangerous gas leaks in the kitchen. Sensor can be easily configured as an alarm unit. The sensor can also sense LPG and Coal Gas.
Features
• High Sensitivity
• Detection Range: 300 - 50,000 ppm Natural Gas
• Fast Response Time: <10s
• Heater Voltage: 5.0V

Ozone (O3) Sensor
Detects and measures Ozone (03) Concentration from 10ppb to 2ppm. Ideal for monitoring air quality or for use in environment and research experiments.
Features
• High Sensitivity
• Detection Range: 10 ppb - 2 ppm O3
• Sensing Resistance: 100kohm - 200Kohm
• Heater Voltage: 6.0V

Air Quality Control Sensor
Air quality sensor for detecting a wide range of gases, including NH3, NOx, alcohol, benzene, smoke and CO2. Ideal for use in office or factory, simply drive and monitoring circuit.
Features
• High Sensitivity
• Stable and Long Life
• Detection Range: 10 - 300 ppm NH3, 10 - 1000 ppm Benzene, 10 - 300 Alcohol
• Heater Voltage: 5.0V

What types of parameters affect the gas sensor?

• Influence of oxygen: The removal of adsorbed negative oxygen ions will give the same electrical effect as adsorption of positive hydrogen ions, protons.

• Influence of different metals: The response to hydrogen is considerably lower for Platinum (Pt) compared with Palladium (Pd) and this has been explained as a difference in the reaction barrier for OH formation. This barrier is higher on Pd than on Pt, which leads to a higher surface coverage on Pd and therefore a higher hydrogen response at given gas concentration.

• Influence of temperature: The metal insulator silicon carbide sensor function over a large temperature ranhe,100-700°C. Their gas response can be divided into two different ranges with the break over points around 600°C. Above 600 °C the gas response of metal insulator silicon carbide sensor to hydrocarbon shows binary behavior. Below 600°C, a more linear response is obtained.