Metal-oxide sensors sensor system

Fig. 2.1. Schematic diagram of design considerations for monolithic or hybrid metal-oxide-based sensor systems...

Suitable methods for CO indoor monitoring are based on using metal oxide sensors (chapter 5.3.2.1), electrochemical cells (chapters 5.3.2.3 and 5.3.2.4), pellis-tors (chapter 53.2.2) and optical methods (chapter 5.3.2.5). An overview of CO-sensors and systems is given in Tab. 5.9. 

Metal oxide sensors (MOS), smart, 22 717 Metal oxide supported catalysts, 5 336-337 coke formation on, 5 267—270 Metal passivation, in industrial water treatment, 26 137 Metal peroxides, 18 410 Metal phosphates, tertiary, 18 840 Metal-phosphorus alloys, 19 59 Metal phthalocyanines, electrochromic materials, 6 572t, 576-577 Metal prefinishing, detersive systems for, 8 413t... 

The central topic of the book was the integration of microhotplate-based metal-oxide gas sensors with the associated circuitry to arrive at single-chip systems. Innovative microhotplate designs, dedicated post-CMOS micromachining steps, and novel system architectures have been developed to reach this goal. The book includes a multitude of building blocks for an application-specific sensor system design based on a modular approach. 

M. Graf, D. Barrettino, M. Zimmermann, A. Hierlemann, and H. Baltes. CMOS Singlechip Metal Oxide Gas Sensing System Based on Microhotplates , Proc. 9th International Meeting on Chemical Sensors (IMCS), Boston, MA, USA, (2002), 141. 

A number of sensor arrays consisting of an assortment of commercial metal oxide gas sensors have been reported [45 7], For controlled tests, the sensors are mounted in an air-tight chamber fitted with gas inlets and outlets for controlled gas flow. Each sensor s heating element is controlled externally and resistance changes of the gas sensors are monitored by a computer data acquisition system. A significant effort in this area exists at the University of Warwick, Coventry, where for many years, sensor arrays, made from discrete Sn02 sensors or miniature integrated sensors, have been studied for ultimate application to food quality and food process control [47, 48]. 

Volatile samples were collected and analysed in the field using the sampling system in conjunction with an array of metal oxide gas sensors. The sensors were calibrated using vapour from an ethanol/water solution and this was used as a reference. A sample of room air was used as a control -background odour. The SPME sampler was introduced to the suspect area, and after sampling the fibre was desorbed into the heated sensor block. When many response patterns are compared it is difficult to visualise... 

GraX M., Barrettino, D., Zimmermann, M., Hierlemann, A., Baltes, H., Hahn, S., Barsan, N. and Weimar, U. (2004a), CMOS monolithic metal-oxide sensor system comprising a microhotplate and associated drcuitry ,/ Sens./.,4(1),9-16. 

M. Pardo, G. SbervegUeri, Electronic olfactory systems based on metal oxide semiconductor sensor arrays. Mrs BuU. 29(10), 703-708 (2004)... 

Fig. 3 Odor map of different cookie sets on the basis of PCA using four metal oxide sensors of C-DAC e-nose system...

From the experimental data, a linear correlation was found between the responses of the different sensors of e-nose system and rancidity parameters obtained by biochemical assays. Therefore, multiple regression analyses were carried out to develop three linear regression equations to predict the FFA value, PV value and TEA value (individually) of the cookies as a function of responses of four metal oxide gas sensors (TGS 830, TGS 2600, TGS 2610 and TGS 2626), which are provided below. 

Two methods are used to measure pH electrometric and chemical indicator (1 7). The most common is electrometric and uses the commercial pH meter with a glass electrode. This procedure is based on the measurement of the difference between the pH of an unknown or test solution and that of a standard solution. The instmment measures the emf developed between the glass electrode and a reference electrode of constant potential. The difference in emf when the electrodes are removed from the standard solution and placed in the test solution is converted to a difference in pH. Electrodes based on metal—metal oxides, eg, antimony—antimony oxide (see Antimony AND ANTIMONY ALLOYS Antimony COMPOUNDS), have also found use as pH sensors (8), especially for industrial appHcations where superior mechanical stabiUty is needed (see Sensors). However, because of the presence of the metallic element, these electrodes suffer from interferences by oxidation—reduction systems in the test solution. 

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