VGSA recognizes gases with only one metal oxide sensor

Unitronic presents a new virtual multifunction gas sensor array (VGSA) at SENSOR+TEST 2011 in Nuremberg (Germany), June 7-9, 2011 at its Booth 638 in Hall 12. The VGSA is an “artificial nose” that can recognize a large number of organic and inorganic compounds, fuel gases and complex mixtures such as tobacco smoke with only one conventional metal oxide sensor. This thus enables an especially cost-effective measurement and analysis of substances in the air.

Conventional sensor arrays are based on a large number of different gas sensors, which all react in their own way to the gas offered and provide a measured value. These individual measured values provide a characteristic fingerprint for each type of gas, which each module is taught by means of a teach-in process. This later enables the identification. The disadvantages of such multi-sensor arrays are that all sensors react differently to humidity, exhibit different long-term drift behavior and also sometimes show a memory effect to gases. This very often requires a repeated complex recalibration of the entire array.
Picture: Unitronic

All of these restrictions cease to exist with Unitronic’s virtual multifunction gas sensor array (VGSA). The determination and analysis of various gases by means of a single cost-effective miniature gas sensor takes place here on the basis of an oxide semiconductor and a special high-sensitivity analysis method based on innovative algorithms and sophisticated electronics.

The acquired sensor parameters contain complex gas-typical, long-term stable patterns and therefore present a sort of fingerprint for each gas. With help of the individual semiconductor sensors, this technology generates several individual sensor signals and therefore corresponds to a virtual sensor array. The type of gas is determined on the basis of the gas caused distortion of periodic temperature jumps. Semiconductor sensors have the characteristic of having different sensitivity reactions to gases at various temperatures. There is an optimum temperature of the sensor for each gas and this is utilized by the “artificial nose” via an intelligent tempering.

Since the “artificial nose” not only analyzes the ohmic resistance of a sensor, as is common practice, but rather the electrical charge shift caused by the target gas, the calculated signal is free of influences from humidity, drift of the absolute value and memory effects.

Fuel gases such as methane, propane and butane, organic compounds such as alcohol, benzene, propanol, ethanol, acetone, toluene, cyclohexane, hydrogen, formaldehyde and carbon monoxide, inorganic compounds such as ammonia, isoflurane, halothane, hydrogen sulfide, trichloroethylene and carbon tetrachloride, but also tobacco smoke and more can be measured with the VGSA. The universal sensor system is therefore not only suitably for a wide variety of applications in the food, bio and pharmaceutical industries, but also equally for a reliable and cost-effective air or fire monitoring.

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