Gas Sensor Microsystem Response to the Odor of Overheated Electrical Wire Insulation
Smirnov A.V., Postgraduate Student of SSU, Grebennikov A.I. 1, Head of Laboratory, Gribov A.N. 1, Postgraduate Student, Simakov V.V. 2, D.Sc., Associate Professor, Head of Chair, Sinev I.V.1, Assistant, Kisin V.V.1, D.Sc., Prof., e-mail:
[email protected] 1
Federal State Budgetary Educational Institution of Higher Vocational Training Saratov State
University named after N.G.Chernyshevsky 2
Federal State Budgetary Educational Institution of Higher Vocational Training Saratov State
Agrarian University named after N.I.Vavilov (SGAU)
We show that by analyzing the gas-sensitive microsystem response to the changes in environment atmosphere composition caused, for instance, by the heating of an electric cable, allows distinguishing between different types of cable insulation coatings. Keywords: gas-sensitive microsystem, aroma sensing, ignition history monitoring
Very promising systems for prevention of ignitions are fire alarm boxes with a gas sensor and a sensitive semi-conductor element [1-3] reacting to the changes in the composition of the atmosphere. A sensor is a microsystem, which can incorporate a heater, a temperature sensor, a gas sensitive layer with a system of contacts and a circuit for a signal processing [4, 5]. Potentials of such microsystems are much wider, than just reaction to a certain signal about a change in the surrounding atmosphere. In particular, with their help it is possible to distinguish a smell of smokes from some burning materials [6], that is, to analyze the history of ignition. Solving of this task is especially important for the objects of aviation and space technologies, surface and underwater ships. The work presents research of the response of a gas-sensitive microsystem to the changes in the atmosphere caused by a gas-separation of the insulation material of an electric cable during its overheating. Besides, a response was also recorded to the change of the environment of a standard industrial optical-electronic fire alarm box IP-212-3SU (Irset-centre Co., Russia), which could be included in the installation instead of such a microsystem. In this case the gas flow was not filtered from the smoke, but the mass of the investigated samples, the speed of heating and the range of temperatures did not differ from the experiment with a multisensor system.
Two kinds of external insulation of the electric cable were studied. Sample № 1 – KG 2x1.5 TU 3500-002 insulation on the basis of isoprene and butadiene synthetic rubbers (Tsvetlit Co., Russia). Sample № 2 – PVS 2x0.75 general purpose insulation on the basis of polyvinylchloride elastron (Oryol Cable Factory Co., Russia). Atmosphere changed owing to emission of gases from the cable insulation during its heating. Researches were done at temperatures from 40 up to 600оС by means of TGA Q500 installation for thermogravimetric analysis (ТGА) (TA Instruments, USA), interfaced with infrared (IR) Nicolet 6700 Fourier spectrometer (Thermo Scientific, USA), and by means of the installation (fig.1). IR absorption spectra were recorded simultaneously with measurement of the weight loss curve with frequencies from 400 up to 4000 cm-1 and were processed by means of OMNIC 8.1 program (Thermo Fisher Scientific Inc., USA). Frequency of measurement of IR spectra was about one spectrum per 10 degrees of heating of a sample. One of the segments of the multisensor system [6] was used as the gas-sensitive microsystem. The temperature of the layer on the basis of tin dioxide was maintained at the level of 300оС with accuracy of 0.3 %. Measurement of the resistance of a segment of the multisensor system was done with Keithley-2000 multimeter (Keithley Instruments, USA). The microsystem’s response was determined as a relation of the resistance of the gas-sensitive layer in the air R0 to R in a gas sample with the gas products emitted during an insulation overheat. TGA installation was loaded with 0.123 g of material with passage of 90 ml/min of the gas-carrier through the spectrometer; for studying of the response of the gas-sensitive microsystem 1.5 g were loaded with passage of 1 ml/min of air through the measuring chamber. The speed of heating was 5о/min. Fig.2 presents the results of ТGА on a derivative for № 1 and № 2. They started to lose their weight at about 200оС and the process continued up to 550–600оС. For sample № 1 two expressed maxima of the speed of loss of weight were observed – at about 380 and 470оС. For № 2 – two maxima, close to 310 and 460оС. It was assumed that the maxima of the speed of loss of weight corresponded to the maxima of the speed of the gas separation. Since the positions of the maxima and a correlation between their intensities essentially differed, the form of curves allowed us to distinguish, which of the samples was exposed to heating. Fig.3 and 4 present the response of the gas-sensitive microsystem and optical densities of gas emissions of the samples on two frequencies at different temperatures, at which maxima are observed of absorption of the gas separation of the samples for the selected frequencies, and corelated with the temperatures, at which the microsystem’s response is also maximal.
It should be taken into account that on the same frequency absorption can be connected with different substances. OMNIC 8.1 software (SW) of IK-spectrometer allowed us to compare the results with the database containing the spectra of absorption of different substances. A version of decoding of the spectra is presented in the table below. Table. Decoding of the spectra of absorption of the gas-separation of the samples with the help of OMNIC 8.1 software Темperature of samples, °С 200 - 250
Possible emissions of sample №1
Possible emissions of sample №2
Carbon disulfide;
Тrаns – 2 hexane; тrаns – 4 - octene; decahydronaphthalene; 1- octanol; 1 – phenylhexane; heptane. Trans – 2 hexane; trans – 4 - octene; decane; hexane; phthalic anhydride; 1,3- dihydro - 1,3 – dioxo isobenzofuran; ethylhexane anhydride; decanoic anhydride.
312
386
464 524
1,4 – dimethyl cyclohexane; undecane; (E)-2- nonene; β-trans- nonene. 1,4 – dimethyl cyclohexane; methyl cyclohexane. Eicosane decahydronaphthalene
2 – ethylhexane anhydride; dibutyl phthalate
As it follows from the table, the composition of the emitted mix of gases changes with an increase in temperature of the samples of the insulation material, i.e. an evolution of its smell is observed. At that, the gas separations of samples № 1 and № 2 essentially differ. For both samples two maxima of the dependence of the response of the gas-sensitive microsystem on the material’s temperature were observed: one – at 300-450оС, and another – at 450-500оС. The structures of the maxima were different. Specific features of the response of the microsystem on the atmospheric change were more pronounced in correlations between the intensities of the maxima. For № 1 a low-temperature maximum response was 2 times bigger
than the high-temperature one, and for the sample № 2 it was 4 times smaller. This can be used as a sign of recognition of an overheated insulation. The industrial optical-electronic alarm box actuated for sample № 1 at 396 оС and did not work in all the range of temperatures for sample № 2. At the same time a noticeable response of the microsystem was observed for both samples at temperatures below 250оС. Thus, a possibility was demonstrated of application of the gas-sensitive microsystem for recording of the dynamics of overheating of a cable insulation, which can be used for an ignition history analysis. The work was done with the support of grant № 13-08-00678 of the Russian Fund of Basic Researches and grant № A/11/73956 of the joint program «Mikhail Lomonosov III» of the Ministry of Education and Science of the Russian Federation and German Service of Academic Exchanges
. Fig.1. Installation for research of the response of the gas-sensitive microsystem to the change of the surrounding atmosphere:1 – heating chamber; 2 – water cooling unit; 3 – filter; 4 – measuring chamber; 5 – multisensor microsystem; 6 – channel fan; 7 – computer
Fig.2. Dependence of the loss of a sample’s weight on its temperature: 1 – sample №1; 2 – sample №2.
Fig.3.Response of the multisensor microsystem and change of the optical density of the gas-separation of sample № 1: 1 – microsystem’s response; 2,3 – optical density on frequencies of 2930 cm-1 and 1377 cm-1.
Fig.4. Response of the multisensor microsystem and change of the optical density of the gas-separation of sample № 2: 1 – microsystem’s response; 2,3 – optical density on frequencies of 2350 cm-1 and 1800 cm-1.
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